shotcrete structural testing of thin liners -...
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Report No. FRA-OR&D-75-91
SHOTCRETE
STRUCTURAL TESTING OF THIN LINERS
AUGUST,1975
FINAL REPORT
Prepared for
Department of Transportation FEDERAL RAILROAD ADMINISTRATION
Washington, D.C. 20590
NOTICE
This document is disseminated under the sponsorship of the Department of Transportation in the interest of in formation exchange. The United States Government assumes no liability for its contents or use thereof.
Technical ~eport Documentation Page
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FRA OR&D 75-91 4 . Title and Subtitle 5 . Report Date
Shotcrete: Structural Testing of Thin Liners August 1975 6 . Performing Orgoni zation Code
,___ ____________ _,
1--------------------------~8. Performing Organization Report No. 7. Author 1 s )
G. Fernandez-Delgado, J. Mahar, E. Cording 9 . Performing Orgoni zotion Nome and Address
Department of Civil Engineering University of Illinois at Urbana-Champaign Urbana, IL 61801
~-------------------------12. Sponsor ing Agency Nome and Address
Federal Railroad Administration Department of Transportation Washington, D. C. 20590
15 . Supplementary Notes
16. Abstract
UILU-ENG-75-2015 10 . Wark Unit No . (TRAIS)
11 . Contract or Grant No .
DOT FR 30022 13. Type of Report and Period Covered
August 1974 - August 1975 Final Report
14. Sponsoring Agency Code
This report presents the results of engineering studies related to the development of new and improved tunnel support systems. Thin shotcrete layers were studied to assess their capacity and behavior as temporary tunnel supports.
The design, construction, and operation of a large-scale test facility simulating a planar tunnel roof with a punching block 2 ft x 2 ft (60.8 cm x 60.8 cm) are described. Preliminary tests were conducted using thin mortar layers to assess the performance of the test device and the principal variables controlling the capacity of the thin liner. Results obtained from these tests were used in the planning and evaluating of the shotcrete test program.
This report describes the development of the test-device, the equipment, and its arrangement and the shotcrete used in the model. The capacity of shotcrete layers for different thickness and strength of shotcrete and shotcrete-rock bond was determined.
Two principal modes of failure, diagonal tension in the shotcrete and progressive separation of the layer from the wall (adhesion), were obtained. When progressive separation occurred and boundaries were present in the model, the layer retained a residual capacity and a bending failure developed for large displacements of the punching block. Steel fiber reinforced shotcrete showed greater ductility but had approximately the same load-carrying capacity as conventional shotcrete.
17. Key Words
Shotcrete; Tunnel Supports; Tunnel Liners; Thin Shotcrete Liners
18, Distribution Statement
Document is available to the public through the Nat ional Technical Information Service, Springfield, VA 22151
19. Security Clossif. (of this report) 20. Security Clossif. (of this page) 21. No . of Pages 22. Price
Unc lass ifi ed Unc lass ifi ed 219
Form DOT F 1700.7 (8-72) Reproduction of completed poge authorized
i.
01101
TF
PREFACE
This study was performed by the Department of Civil Engineering
of the University of Illinois at Urbana-Champaign, Urbana, Illinois from
August 1974 to August 1975. The pr~ject was sponsored by the Federal Rail
road Administration, Department of Transportation, through contract No.
DOT FR 30022, under the technical direction of Mr. William N. Lucke. Super
vision and coordination of the entire project was performed by Dr. Stanley
Paul. Dr. Paul also contributed many ideas and participated in the lively
discussions which stemmed from this work.
Mr. Harvey Parker contributed many original ideas and did much
to assist in the performance and analysis of these tests.
Construction of the test facility, shooting of the specimens and
experimental and field testing was assisted by R. Castelli, L. Lorig, and
W. Wue 11 ner.
Special assistance in organizing and developing the shotcrete
operation and providing good quality shotcrete was given by Mr. Warren
Alvarez and Mr. Jan Blanck.
Many valuable suggestions on the geotechnical significance of the
study and on the validity of the tests were provided by Dr. R. B. Peck and
Dr. 0. U. Deere who serve as consultants to the project.
The authors also wish to thank Mr. Paul Diemert and Mr. E. R.
Roger~ of Contractors Warehouse Inc. for providing us with a Reed Shotcrete
machine at a greatly reduced price.
iii
TABLE OF CONTENTS
Chapter Page
1 .
2.
. INTRODUCTION 1- l
3.
4.
5.
DESCRIPTION OF TEST DEVICE . . . . . 2-1
2 .1 2.2 2.3 2.4
REACTION ABUTMENT HYDRAULIC RAMS . . . . . . . FIXED WALL AND MOVABLE BLOCKS INSTRUMENTATION ..
PRELIMINARY TESTING PROGRAM .....
2-1 2-3 2-5 2-9
3-1
3.1 PREPARATION OF THE SPECIMENS . . . . . . 3-1 3.2 GEOMETRY AND BOUNDARY CONDITIONS OF TESTS ..... 3-2 3.3 MAIN VARIABLES AFFECTING THE STRUCTURAL BEHAVIOR OF
THE MORTAR LAYER. . . . . 3-4 3.4 LOADING PROCEDURE . . . . 3-14 3.5 TEST RESULTS . . . . . . . . 3-15 3.6 SIGNIFICANCE OF VARIABLES 3-71 3.7 CONCLUSIONS 3-83
SHOTCRETE TESTS ..... .
4 .1 4.2 4.3 4.4 4.5
INTRODUCTION .... SHOTCRETE OPERATION . SHOTCRETE TEST PROGRAM TEST RESULTS .................. . EVALUATION OF VARIABLES INFLUENCING THE STRUCTURAL BEHAVIOR OF THE LAYER
SUMMARY AND CONCLUSIONS ........ .
5. l 5.2 5.3
MAXIMUM RESISTANCE OF THE LAYER RESIDUAL RESISTANCE GENERAL CONCLUSIONS
4-1
4-1 4-2 4-19 4-26
4-59
5-1
5-1 5-3 5-4
REFERENCES
APPENDIX A
APPENDIX B
APPENDIX C
R-1
A-1
B4 l
C-1
V
LIST OF TABLES
Table Page
3. 1 MORTAR COMPONENTS IN 260 LB (118 kgm) BATCH 3-1
3.2 DIMENSIONS OF MORTAR LAYER . . . . . 3-6
3.3 MATERIAL PROPERTIES OF TEST SPECIMENS 3-12
3.4 MORTAR TEST RESULTS . ...... 3-27
3.5 VARIABLES COMPARED BETWEEN TESTS 3-72
4. 1 DRY MIX PROPORTIONS WITHOUT FIBER 4-5
4.2 DRY MIX PROPORTIONS WITH FIBER 4-6
4.3 MATERIAL PROPERTIES OF SHOTCRETE LAYERS . 4-20
4.4 SHOTCRETE LAYER TEST RESULTS ..... 4-28
4.5 VARIABLES COMPARED IN THE SHOTCRETE LAYER TESTS 4-61
C-1 SUMMARY OF ADHESION-TEST RESULTS TESTS S3 & S4 . C-5
C-2 SUMMARY OF ADHESION-TEST RESULTS TESTS S9 & SlO, C-6
C-3 SUMMARY OF ADHESION-TEST RESULTS TESTS S7 & S8. C-7
C-4 SUMMARY OF ADHESION-TEST RESULTS TESTS S11 & S12 C-8
vii
LIST OF FIGURES
Figure Page
l. l TYPICAL GEOMETRIC CONFIGURATIONS AND LOADING CONDITIONS IN TUNNELS INTERSECTED BY FLAT-LYING DISCONTINUITIES OR IN FLAT-ROOFED OPENINGS IN JOINTED ROCK . . . . . . . . . 1-3
l. 2 FIELD EXAMPLES OF TUNNELING IN 11 BLOCKY 11 ROCK MASS . . . 1-4
l. 3 PLANAR GEOMETRY OF TEST DEVICE FOR STRUCTURAL TESTS ON SHOTCRETE LAYERS . . . . . . . . . . . . . . . . . . . 1-5
1.4 FUTURE SHOTCRETE TESTS INVOLVING OTHER ROCK GEOMETRIES 1-7
2.1 OVERALL VIEW OF THE TESTING DEVICE 2-2
2.2 DETAIL OF RAMS-ABUTMENT CONNECTION 2-2
2.3 STEEL FRAME ASSURING VERTICAL AND HORIZONTAL ALIGMENT OF THE RAMS . . . . . . . . . . . . . . . . . 2-4
2.4 DETAIL VIEW OF RAM-MOVABLE BLOCK CONNECTION . . . . . . . 2-4
2.5 DIMENSIONS OF SURFACE SLAB AND HOLE PATTERNS FOR ATTACHING THEM . . . . . . . . . . . . 2-6
2.6 FRONT FACE OF THE FIXED WALL . . . . . . . . . . 2-7
2.7 FORMS AND REINFORCEMENT FOR THE FIXED SIDE BLOCKS 2-8
2.8 FORM AND REINFORCEMENT FOR THE MOVABLE BLOCKS . . 2-10
2.9 FORMS, MESH REINFORCEMENT AND THREADED INSERTS FOR SURFACE SLABS . . . . . . . . . . . . . . . . . . . . . . . . 2-10
2.10 FRONTAL DIAL GAGES AND STEEL FRAME SUPPORTING THEM 2-12
2.11 MORTAR SURFACE-DIAL GAGE BRACKET CONNECTION . 2-12
3. l PRE-TEST SURFACE CRACKS IN TEST NO. l . . . 3-3
3.2 APPEARANCE OF SPECIMEN NOS. 5 AND 6 IMMEDIATELY BEFORE TESTING . . . . . . . . . . . . . . . . . . . . . . . . 3-3
3.3 USE OF 6 X 18 IN. (152 X 457 MM) PLATES IN TEST NOS. 13 AND 14 TO SIMULATE ROCK BOLTING . . . . . . . . . . . . 3-5
ix
3.4 USE OF 16 X 24 IN. (406 X 609 MM) PLATES IN TEST NOS. 17 AND 18 TO SIMULATE ROC K BOLTING ........... , . , 3-5
3.5 SCHEMATIC DIAGRAM SHOWING TWO TYPES OF FAILURE MODES. , . . 3-8
3.6 FRONTAL VIEW OF FAILED MORTAR LAYER WITH NO CRACKS AT THE MOVABLE-FIXED BLOCK CONTACT . . . . . . . . . . . . 3-17
3.7 SCHEMATIC VIEW OF SHOTCRETE LAYER DEFLECTION AFTER SEPARATION STARTS . . . . . . . . . . . . . . . . . 3-17
3.8 MORTAR LAYERS FAILED BY SEPARATION OF MORTAR LAYER FROM THE SURFACE SLAB . . . . . . . . . . . . . . . . . . 3-19
3.9 STEEL PLATES PROVIDING RESTRAI NT TO ADHESION FAILURE PROPAGATION , · · , · · , · · · · · · · , · , · 3-19
3.10 TOP VIEW OF MORTAR CRACKING PATTERN IN TEST NO. 17 , 3-20
3.11 VERTICAL CRACKS IN THE MORTAR LAYER DUE TO BENDING STRESSES DEVELOPED BY LOAD ING PROCESS IN TEST NO. 16 · · • • , • · · 3-21
3.12 TOP VIEW OF ADHESION FAILURE DEVELOPED BETWEEN THE MORTAR LAYER AND THE CONCRETE SLAB COVERI NG THE MOVABLE BLOCK IN TEST NO. 15 · , · · · , · · , · · · · , · , , · · · , · · 3-22
3.13 MORTAR SURFACE CRACKS DEVELOPED ALONG PRE-LOADING WEAKNESS ZONES 3-22 . . . . . . . . . . . . . . . .. . . .. ..... ,
3.14 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACE-MENT RELATIONSHIPS FOUND IN MORTAR LAYERS , , . , . . 3-24
3 .15 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml & M2 , . . , , . , · , , , , , · , , · · , · , 3-28
3 .16 UNIT LENGTH RESISTANCE VS MOVABLE BLOC K DISPLACEMENTS TEST M3 & M4 , , , , , · , , , , , , , · , , , , , , ,
3.17 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M5 & M6 , ....... , . , , , ..... , . ,
3.18 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M7 & MS , , .. , , , · . , , , , , . , , , , , ,
3.19 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST M9 & Ml O . . . . . . . . , . . . . . , . , . . , ,
3.20 ,UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml l & Ml 2 , . , . . . , . . . . , . . , . . . , ,
3.21 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST Ml 3 & Ml 4 . , , , · , , , , · , , , , , , , · , ·
3.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TEST f~l 5 & Ml 6 , . . , , , , . , . , , . . , . , , , ,
3.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
.
.
• . 3-29
3-30
3-31
3-32
3-33
3-34
. ' 3-35
TEST Ml7 & Ml8 , ... , , , ... , ,··, , .. , , , . . . 3-36
X
3.24 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml 3-38
3.25 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M2 3-39
3.26 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M3 3-40
3.27 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M4 . 3-41
3.28 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M5 3-42
3.29 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M6 . 3-43
3.30 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M7 3-44
3.31 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST M9 3-45
3.32 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Mll. 3-46
3.33 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml2. 3-47
3.34 FRONT FACE DISPLACEMENT OF LAYER W.R ,T. FLOOR: TEST Ml3(1) 3-48
3.35 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml4(1) , 3-49
3.36 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml5(1) . 3-50
3.37 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR: TEST Ml6(1) 3-51
3.38 FRONT FACE DISPLACEMENT OF LAYER W.R.T, FLOOR: TEST Ml7(1) 3-52
3.39 FRONT FACE DISPLACEMENT OF LAYER W.R.T, FLOOR: TEST Ml8(1) .. 3-53
3.40 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST M13(2) .. 3-55
3.41 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml4(2) .. 3-56
3.42 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml5(2),.3-57
3.43 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml6(2) .. 3-58
3.44 FRONT FACE DISPLACEMENT WITH RESPECT TO THE- FLOOR: TEST Ml7(2) .. 3-59
3.45 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR: TEST Ml8(2) .. 3-60
3.46 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER: TEST Ml & M2 .
3.47 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER: TEST M3 & M4 ..
xi
' . ' . ..3-63
.. 3-64
3.48 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST MS & M6 ...
3.49 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M7 & M9 .. ,
3.50 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST Ml 1 & Ml 2 . .
3. 51 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M13 & M14 ..
3.52 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M15 & M16 ..
3. 53 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER TEST M17 & M18 ..
3.54 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Ml ,M2 ,M7 & MB . . . . . . . . . . . . . . . . .
3.55 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll ,Ml2,Ml7 & Ml8 ............. , .
3.56 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll,Ml2,M13 & M14 ............. , .
3.57 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS M3 ,M7 & M9 . . . . . . . . . . . . . . . . . .
3.58 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Mll ,Ml2,M15 & Ml6 .............. .
3-65
3-66
I ~ I f 3-67
... , 3-68
3-69
3-70
3-74
3-76
3-78
3-80
3-81
4.1 FRONTAL VIEW OF TESTING DEVICE vJITH PLYWOOD WINGWALLS 4-3
4.2 CLOSE-UP SHOWING VERTICAL SCREED WIRES AND TAPES SURFACE .. , 4-3
4.3 FRONTAL VIEW OF COTTON-FILLED MOVABLE BLOCK-SURROUNDING SLOTS .....
4.4 GRADATION CURVES .
4.5 NOZZLE CLOSE-UP . .. 4.6 SCHEMATIC ARRANGEMENT OF THE SHOTCRETE EQUIPMENT
4.7 ARRANGEMENT OF SHOOTING EQUIPMENT .....
4.8 CLOSE-UP VIEW OF BELT CONVEYOR AND POWERED GUN
4.9 FIBER SCREENING USING 1-IN. (2.54 CM) SIZE SIEVE
. ' .
, . 4-4
4-7
4-9
, . 4-10
4-11
4-11
4-13
4. l O \>JARM-U P SHOO TI NG AGAINST PLYWOOD WALL . . . . . . . . . , . . . 4-13
Xii
4.11 STRENGTH-SPECIMENS PANEL BEING FILLED UP ... ' . .. , , , . 4-14
4.12 FINISHED STRENGTH-SPECIMENS PANEL . . . . . ' . ' . ' . 4.13 PATTERN OF SHOOTING , , ... , , •• ! ' • !I •• . ' ,
4.14 FRONTAL VIEW OF SHOTCRETE LAYERS IMMEDIATELY AFTER TRIMMING , . , ! • • , • • • , • , • • • , • , , • • I •
. , , 4-14
, . 4-15
, .. 4-18
4. 15 FRONTAL VIEW OF SHOTCRETE LAYERS DURING CURING PROCESS . , . , 4-18
4.16 COMBINED SHOTCRETE-SLAB SECTION AND CORRESPONDENT ADHESIVE TEST SAMPLES , . , ...... , . , . , .. , , . , , , , 4-24
4.17 ADHESIVE TEST SAMPLES AFTER TESTING ... ~ , ... , 4-24
4.18 ADHESIVE STRENGTH VS COMPRESSIVE STRENGTH OF THE SHOTCRETE LAYERS I I I I I , j t I .. I • I f I ~ I f p f ~ I t
4.19 FRONTAL VIEW OF FAILED SURFACES IN TEST NOS. l AND 2 , , , .. , 4-27
4.20 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACE-MENTS RELATIONSHIP FOUND IN SHOTCRETE LAYERS , , , , . , . , . 4-30
4.21 UNIT LENGTH RE~ISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl & S2 , . . . . . , , , . . . . . , . , , , .
4.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S3 & S4 , . , . . . , . . . , . , . , . . . . . .
4.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S5 & S6 . . . . , . . . . . . . . . . . . . . .
4.24 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S7 & S8 . . . . . , , . , . . . . . . . , , , .
4.25 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S9 & Sl O . . . . . , , . , . . . . . . . . . , .
4.26 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl l & Sl 2 . . . . . . . . . . . . . . . . . . .
4.27 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl 3 & Sl 4 . , . , . . . . . . . . . . . . . , .
4. 28 UNIT LENGTH RESISTANCE VS f110VABLE BLOCK DISPLACEMENTS
.
.
•
.
.
•
•
.
.
. . 4-31
4-32
• . 4-33
. . 4-34
' . 4-35
. 4-36
' 4-37
TESTS Sl5 & Sl6 . , . , , , .... , . . . . . . . .. . 4-38
4.29 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl ... , ....... , .. , , . , 4-42
4.30 FRONT FACE DISPLACE~ENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S2 .... , ... , . , .... , ..
4.31 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT
4-43
TO THE FLOOR TEST S3 ..... , ....... , . , . . 4-44
xiii
4.32 FRONT FACE DISPLAC81ENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S4 ................. .
4.33 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S5 ................. .
4.34 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S6 ................. .
4.35 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST S7 ................. .
4.36 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST SB ............... , . ,
4. 37 FRONT FACE DISPLACEMENT OF SHOTCRETE LA-YER WITH RESPECT TO THE FLOOR TEST S9 ............. , ... ,
4.38 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST SlO ................ .
4.39 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sll ................ .
4.40 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl2
4.41 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl3 ............ , ... .
4.42 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl 4 . . . . . . . . . . . . . . . , .
4.43 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR TEST Sl5 ............... .
4.44 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S3 & S9 . . . . . . . . . . . . . , . . . . . .
4.45 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4 & Sl O . . . . . . . . . . . . . . . . . . . .
4.46 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS Sl , S2, Sl 3 & Sl 4 . . . . . . . . , . . . . . .
4.47 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4, S6, SB & Sl2 ....... , ...... .
4.48 UNIT LENGTH RESISTA~CE VS MOVABLE BLOCK DISPLACEMENTS TESTS S4 & Sl6 .............. .
5.1 MAXIMUM RAM LOAD VS MEASURED ADHESIVE STRENGTH ..
5.2 BEAM MODELS USED IN RESIDUAL CAPACITY CALCULATIONS
.
.
.
B-2 ROUGHNESS MEASURING DEVICE .... ' .
. . .
'
. .
' .
.
4-45
4-'46
4-47
4-48
4 .. 49
4-50
4-51
4-52
4-53
4-54
4-55
4-56
4-62
4-63
4-66
4-71
4-73
5-2
5-4
B-2
B-2 TEST 1 (11/4/74) COLD ROLLED STEEL (VERY SMOOTH) . . . . B-3 xiv
l
B-3
B-4
. C-1
C-2
TEST 1 (11/12/74) MID-NORTH FINISHED SIDE
TEST 3 (11/11/74) SOUTH TOP FORM SIDE ..
FRONT VIEW OF THE TESTING DEVICE AND MONITORING SYSTEM
SAMPLE ATTACHING SCHEME AND GAGE MEASURING STRAIN ACROSS THE CONTACT ........ .
B-4
B-5
C-2
C-2
C-3 FAILED ADHESIVE TEST SAMPLE ................ C-3
C-4 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS SlO .................... C-9
C-5 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS S9, .................. . C-1O
xv
•
•
CHAPTER l
INTRODUCTION
A device was constructed to study and test the structural behavior
of thin shotcrete linings under load in a configuration that simulates
loosening behavior in a jointed rock tunnel. In the first series of tests
the thin shotcrete lining was replaced by a sand-cement mortar layer which
was troweled onto the surface of the testing device. These tests were used
to evaluate the performance of the testing apparatus and the modes of failure
and performance of a material having properties similar to shotcrete. A
second series of tests were conducted on shotcrete which was applied to
the surface of the model in the same manner used for placing shotcrete under
ground. In these tests the major variables that influence the support capac
ity of a thin shotcrete lining in a plane configuration were investigated;
the results of these tests, application of the shotcrete, and performance
of the test device will be described herein.
The ultimate objective of this testing program is to develop a
more rational procedure for the design of the thin shotcrete linings used
as support in tunnels driven through jointed rock. One means of develop
ing such procedures is to study the structural behavior of thin linings
using physical models which represent actual conditions encountered in
tunnels. The approach emp loyed in this project was to perform a series
of structural load tests in which parameters of shotcrete and pertinent
geology were methodicall y varied while keeping the configura tion of the
tunnel surface constant. As it was impractical to perform enough tests
l - l
to cover the full range of variables, procedures to predict the struc
tural behavior of a lining subject to untested conditions were developed,
based on the results obtained from the tests. These procedures, involving
simple hand calculations as well as computer analyses using finite element
methods, will make possible the construction of design charts to be used
for est imating the maximum load that a given lining could support in a
given set of field conditions.
Two types of variables were studied in the determination of the
load-deformation characteristics of the thin shotcrete linings. Geological
va ri ables included (1) the nature of rock surface as it affects adhesion be
tween the shotcrete and the rock and (2) the boundary conditions of the
shotcrete layer . Other geological variables such as ftlJing of joints and
filling of shotcrete between their surfaces were not studj ed. The second
type of variable involved the strength and deformability of the shotcrete;
they were varied by changing the thickness, time of curing, and type of
reinforcement. The proportion: of the materials used in the shotcrete mix
were kept constant for all the tests.
Typical geometric configurat ion that has been observed in tunnels
driven through flat-lying sedimentary rocks, r oc ks containing horizontal
stress relief joints and flat-roofed openings in jointed rock are shown
schematically in Fig. l .l. Sketches of actual tunnels having a similar
geometry are shown in Fig. 1.2. In actual tunnels, there are a very large
number of possible rock block geometries as well as variations in the rela
tive sizes of the blocks. This last variable however could be standardized
usin g a suitable scaling factor.
l -2
'
(a) (b)
FIGURE 1. 1 TYPICAL GEOMETRIC CONFIGURATIONS AND LOADING CONDITIONS IN TUNNELS INTERSECTED BY FLAT-LYING DISCONTINUITIES OR IN FLAT-ROOFED OPENINGS IN JOINTED ROCK
1-3
FIGURE l .2 FIELD EXAMPLES OF TUNNELING IN 11 BLOCKY 11 RCCK MASSES
(Craig, C. L. and Brockman, L. R., 1971)
1-4
t.
A testing device was designed to simulate the flat-roof condition
yet have the versatility to model other geometric configurat ions (Fig. 1.3).
The model was set up so that ·a con tinuous record of the l ining loads and
deformations was obtained throughout the tests. The forc e on the shotcrete
Fixed block Movable block
Hydraulic ram
Fixed bl ock
Shotcrete
FIGURE 1.3 PLANAR GEOMETRY OF TEST DEVICE FOR STRUCTURAL TESTS ON SHOTCRETE LAY ERS
lining was applied using hydraulic rams so that loads could be controlled
and measured accurately. The rams selected for use on this project are
controlled electronically to provide either load or de formation rate control.
When combined with incremental loadin g, this system allows observation of
lining behavior at various load level s.
A system of reinforced concrete blocks was dev i sed to simulate
the basic tunnel geometry (Fig. 1. 3). A movable block was at t ached to a
hydraulic ram to represent a roc k block as it applies load t o a thin shot
crete lining. Adjacent fixed bl ocks simulated the sta t ionary rock mass
within the tunnel. The fixed bloc ks were attached to the labora t ory test
floor with prestressed rods. The model was set up so that the movable block
was pushed horizontally r ather than falling downward as woul d take place in
1-5
a tunnel. This adjustment avoided some problems associated with the dead
weight of the block, allowed the test device to be secured to the laboratory
floor more easily, and provided a more convenient test surface for placing
the shotcrete. In addition, it reduced danger from spalling of shotcrete
during testing while measurements were being made. In the original design
of the loading system only one movable block was provided, but it became
apparent that preparation for placing the shotcrete for each test would be
so extensive that it would be desirable to have at least two structural tests
for each shooting. Therefore, a second movable block was added below the
first. This arrangement also provided a means for checking possible varia
tions in shotcrete properties and behavior associated with shotcrete ap
plication by performing two identical tests on shotcrete applied at the
same time.
In order to study the effects of surface adhesion, and to provide
various surfaces that are typical of the tunnel environment, provisions were
made for changing the surface of the fixed and movable blocks. This was
accomplished by bolting 3 in. (7.62 cm) thick mesh-reinforced concrete
slabs to the fixed and movable blocks. The surface roughness of these
slabs was varied to simulate different joint surfaces. The shotcrete was
applied directly to these slabs.
In the next chapter the test device is described in greater de
tail. Chapter 3 outlines the test program and the results obtained from
the preliminary mortar tests. The characteristics and results obtained
from the structural tests on thin shotcrete linings in a planar configur
ation are described in Chapter 4. Finally, in Chapter 5, the conclusions
and recommendations drawn from the testing program are presented.
1-6
Geometric configurations other than a planar surface will be
studied and tested in future work (Fig. 1.4). These configurations will
be obtained by replacing the existing blocks or adding new sections with
different shapes. The movable blocks, load arrangement and test proce
dures will remain essentially the same. These tests will be used to de
velop design criteria for thin shotcrete linings and a large range of
geologic conditions.
Fixed block Movable block
Shotcrete
Hydraulic ram
Fixed block
e1 and e2 are variable
Fixed block Movable b 1 ock
Hydraulic ram
Fixed block
FIGURE 1.4 FUTURE SHOTCRETE TESTS INVOLVING OTHER ROC K GEOMETRIES
1-7
CHAPTER 2
DESCRIPTION OF TEST DEVICE
A testing scheme, versatile enough to be adapted to the variation
of the chosen parameters, was designed. This scheme is shown in the photo
graph of Fig. 2.1 and consists of (l) the reaction abutment on the left,
which remains unaltered from test to test; (2) the test wall on the right
with fixed and movable portions, the front surfaces of which are covered
with the thin shotcrete layer; and (3) the two hydraulic rams, which thrust
against the reaction abutment to apply load to the movable portion of the
wall. The test device and instrumentation are further described in the fol
lowing sections.
2.1 REACTION ABUTMENT
The reaction abutment shown in Fig. 2.2 acted as a reaction to
the force applied through the rams to the thin shotcrete layers. It was
attached to the floor of the test area by three steel bolts that were pre
stressed to 50 kips (220 kilonewtons). The abutment was similar to those
employed as reactions for the forces applied during the testing of cylin
drical liners previously performed in the University of Illinois laboratory
(Parker, et al., 1973). Successful performance of the abutment during the
previous tests, which required loads equal or greater than those applied
in this test program indicated that the abutment would perform adequately.
2-1
FIGURE 2.1 OVERALL VIEW OF THE TESTING DEVICE
FIGURE 2.2 DETAIL OF RAMS-ABUTMENT CONNECTION
2-2
2.2 HYDRAULIC RAMS
Two MTS hydraulic rams, shown in Fig. 2.3, each 85 in. (216 cm)
long with a 5-in. (12.7-cm) stroke and able to apply a maximum load of
100 kips (440 kilonewtons) in either tension or compression were used in
these tests. Each loading unit consisted of the ram and its valve system,
a load cell, and a ball and socket seating arrangement at the connection
between the movable block and the loading unit. Details of the basic
structure of the ram and its characteristics are given in Appendix A.
The rams were located 21 in. (53.3 cm) and 48 in. (122 cm) above the floor,
and were leveled and aligned so that the axial thrust would be perpendicu-
lar to the wall. They were bolted to a steel plate embedded in the con-
crete abutment. A steel frame providing intermediate support for the rams
was located 36 in. (91.4 cm) from the reaction abutment as shown in Fig.
2.3. These supports were used to set and maintain the vertical and hori
zontal alignment of the loading unit. The load in the rams was transmitted
to the movable blocks through al in. (2.54 cm) spherical steel seat at the
end of the rams and the movable blocks (Fig. 2.4). The sphere was used to
transfer the loads so that moments would not be induced in the movable blocks.
The rams were controlled electronically to provide a predeter
mined rate of loading or rate of displacement of the movable block. This
control allowed the simulation of different types of loading on the shot
crete specimen. It was also possible to stop the displacement or load
application at any desired load level and maintain that level for any time
span. Thus, the test can be performed continuously, or in increments,
2-3
' FIGURE 2.3 STEEL FRAME ASSURING VERTICAL AND HORIZONTAL
ALIGNMENT OF THE RAMS
FIGURE 2.4 DETAIL VIEW OF RAM-MOVABLE BLOCK CONNECTION
2-4
allowing the behavio r of the shotcrete to be investigated at any stage
during the test. The rate of loading, or displacement, was controlled by
electronic regulation of the hydraulic flow into the rams . The load
deformation output of the rams was monitored with an x-y recorder.
2.3 FIXED WALL AND MOVABLE BLOCKS
The wall on which the shotcrete layer was applied is 10 ft (305
cm) long and 6 ft 6 in. (198 cm) high. Two 2 x 2 ft (61.0 x 61 .0 cm) mov
able blocks, one above the other, were located in the middle of the wall.
The back of this wall is shown in the photograph of Fig. 2.1. A front
view of the wall illustrating the relative position of the concrete blocks
comprising the test model is shown in Fig. 2.5. A photograph of this same
frontal view is presen ted in Fig. 2.6. The fixed blocks were held to the
test floor with four vertical bolts extending through the entire wall.
These bolts were prestressed to 25 kips (110 kilonewtons) thereby producing
a rigid structure on which the shotcrete was placed. During some early
tests the blocks of concrete were not grouted to the floor. Early tests
were also conducted using only one movable block. To increas e the stiff
ness of the model and the number of tests that could be conducted from a
single shotcrete application, an extra movable block was added and the con
crete blocks were grouted to the floor . In order to provide the desired
bonding conditions without replacing the fixed or movable blocks, precast
facing slabs were placed on the front or the wall. These slabs were 3 in.
(7.62 cm) thick and were bolted and grouted to both the fixed and movable
blocks.
2-5
Test floor 1•
II 11 11 II
" 11 11 ,, ,, 11 II II II ,, ,, II II II
1/2 11 Steel plates
,. I 611
-..tJ
6"
6" , 6"
10 1 -0 11
Movable block
4 1 -0 11
Hold-down bolts
l -1/2 1
5'
~ 6"
L 6"
2 ':..Q" 6"
6"r
111 - 2 1 -0 11
I' ,. I Scale
FIGURE 2.5 DIMENSIONS OF SURFACE SLAB AND HOLE PATTERNS FOR ATTACHING THEM
2-6
FIGURE 2.6 FRONT FACE OF THE FIXED WALL
The fixed walls were used in this model to simulate a stable rock
mass in a tunnel roof or wall. They were constructed of reinforced concrete
and were provided with horizontal holes for attachmen t of the surface slabs.
Concrete with a nominal 5000 psi (350 kg/cm2) compressive strength and
obtained from a local ready mix plant was used. The forms and reinforce
ment for the fixed blocks are shown in Fig . 2.7. A similar form was used
for the long concrete block placed across the top of the model (Fig. 2.5).
The reinforcing bar cage shown in Fig. 2.7 consisted of No. 3 and No. 6
deformed bars; the larger diameter vertical bars being placed 1 in. (2.54 cm)
2-7
FIGURE 2.7 FORMS AND REINFORCEMENT FOR THE FIXED SIDE BLOCKS
from the fr ont face of the blocks where the compression stresses due to
forward bending of the walls would be high. The pres tressing bolts used
to attach the fixed blocks and transverse beam to the test floor were placed
through two, 2.5 in. (6.35 cm) diameter pipes in each block. Eight steel
pipes, l in. (2.54 cm) 0.D., were placed l ft (30.5 cm) apart in two rows
for attachment of the surface slabs. A steel plate 5 ft (150 cm) by l ft
(30.5 cm) by 1/2 in. (1.27 cm) thick was cast into the fixed walls adja
cent to the movable blocks . A fr ont view of this plate is show in Fig. 2.5.
2-8
The lower movable block and its connection with the rams was
supported on a concrete base block (Fig. 2.5). The base support block
was 9 in. (22.9 cm) tall, with dimensions of 2 ft (61.0 cm) by l ft (30.5
cm) and was lightly reinforced. This block was grouted to the floor and
its surfaceleveled. Both movable concrete blocks rested on a ball and
groove arrangement like those shown in Fig. 2.6. This device served to
guide the movable blocks and minimize the friction between them and their
support. The upper one rested on a steel support bolted to the plates
located on sides of the fixed walls (Fig. 2.5). A ball and groove guide
was also employed at the top of each movable block. This served to pre
vent the blocks from tilting forward or backward. The movable blocks 2 ft
x 2 ft x l ft (61.0 cm x 61.0 cm x 30.5 cm) were cast in the form shown in
Fig. 2.8. In this figure the reinforcing cage, which consisted of No. 6
deformed bars, can also be seen.
The surface slabs were attached to each block by four, 1/4 in.
(0.635 cm) diameter steel rods which were threaded into nuts cast in the
slabs and were bolted on the back side of the blocks. The forms for the
surface slabs were made of steel so that deflections from the wet concrete
would be minimized and maximum reusability would be assured. One of these
forms including the mesh reinforcement and threaded inserts for the attach
ing bars is shown in Fig. 2.9.
2.4 INSTRUMENTATION
Two basic types of deformation measurements were made in the
mortar tests; the displacement of the mortar layer with respect to the
2-9
FIGURE 2.8 FORM AND REINFORCEMENT FOR THE MOVABLE BLOCKS
FIGURE 2.9 FORMS, MESH REINFORCEMENT AND THREADED INSERTS FOR SURFACE SLABS
2- l 0
fixed walls and the floor, and the strains occurring in the mortar layer.
The last set of measurements was discontinued in the shotcrete tests.
Displacement measurements were made with dial gages having sen
sitivities of 0.001 and 0.0001 in. (2.54 x 10-3 cm) and (2.54 x 10-4 cm).
These gages were attached to a steel frame which was bolted to the floor
(Fig. 2.10). These dial gages, located 10 in. (25.4 cm) apart on a hori
zontal line at the midheight of the mortar or shotcrete layer, were used
to measure the relative displacement of the layer with respect to the floor.
Because of irregularities in the layer surface, and to avoid damage of the
dial gages after failure of the shotcrete, the gages were not in direct
contact with the layer; the contact was made through steel plates pre
viously grouted to the surface, as shown in Fig. 2.11. Three dial gages
were mounted on the back of the movable block (Fig. 2.4) such that their
plunger could bear directly against the back of the fixed block. These
gages were used to monitor the relative horizontal displacement between
the movable block and the fixed walls. The triangular arrangement of
these gages also provided a means for detecting any tilting of the movable
block caused by eccentric loading or non-uniform resistance of the mortar
layer. Another set of dial gages recorded the displacements of the back
of the fixed walls with respect to the laboratory floor. These gages, as
shown in Fig. 2. 11, were located at different distances from the movable
blocks and at different elevations relative to the floor in order to de
tect any rotation of the walls that might occur during the loading process.
During the initial tests a Whittemore gage was used to measure
the relative displacement of points located 10 in. (25.4 cm) apart on a
2-11
FIGURE 2.10 FRONTAL DIAL GAGES AND STEEL FRAME SUPPORTING THEM
FIGURE 2. 11 MORTAR SURFACE-DIAL GAGE BRACKET CONNECTION
2-12
horizontal line at midheight on the outer surface of the mortar layers.
Most of these Whittemore points were located on the same steel bearing
plates that were used as surface reference points for the dial gages.
The loading was performed incrementally, with dial gage and Whittemore
readings taken at the end of each increment. After each load increment,
up to the peak, the load was maintained constant while the readings were
taken. After the resistance of the layer started to decrease, the test
ing procedure was changed. For some tests the constant rate of loading
was continued until failure of the layer, without stopping for additional
measurements. For most tests, however, the loading was changed to a con
stant strain rate, and controlled such that readings could be taken at pre
determined deformation increments to determine the full load-deflection
curve for the mortar or shotcrete layer.
2-13
CHAPTER 3
PREL.IMINARY TESTING PROGRAM
A preliminary investigation using sand-cement mortar as a sub
stitute for shotcrete was carried out to determine the performance of the
test device, to assess the main variables influencing the mode of failure
of thin linings, and finally, to check the repeatability of test results.
3.1 PREPARATION OF THE SPECIMENS
In all tests, the mortar of the thin layer consisted of the same
mix design. Water, sand and cement were mixed in 260 lb (118 kgms) batches
in a rotatory, pan-type mixer. Table 3.1 shows the amounts and relative
percentages of the three mix components. The water/cement ratio of the
mix was 0.54 and 0.52. In all of the tests approximately l in. (2.54 cm)
TABLE 3.1
MORTAR COMPONENTS IN 260 LB (118 kgm) BATCH
Mix components Weight Percentage of the lb (kgms) total mix
Cement 65 (29.5) 25.0
Sand 160 (72.6) 61.5
Water, tests 1-4 35 (15.9) 13.5
tests 5-18 34 (15.5)
of mortar was placed on the fixed and movable blocks. A thin layer about
3-1
1/2 in. (1.25 cm) was applied, first, with a trowel, and the remainder
placed approximately 1/2 hr later using the same procedure . This two
stage appli cation was used to avoid sloughing of the mortar layer which
occurred when it was placed in one application. The mortar layer was
cured by cover ing it with wetted burlap which hung down the front of the
wall. The bur lap was continuously wetted during the curing period until
the specimen was ready to be tested. This procedure was intended to simu
late the high humidity typically found in underground openings. Control
specimens werecast to determine the approximate strength characteristics
of the layer material and were cured in a fog room. In test Nos. l to 4,
cracks were observed on the exposed surface of the mortar layer at the end
of the curing period (Fig. 3.1). These cracks were beli eved to be the re
sult of sloughing of the second layer of mortar rather than by shrinkage
of the material. Pre-test cracks were not present in the remainin g
tests where the water content of the mortar was slightly reduced, and
greater pressure was used in applying the mortar to the wal l. Figure 3.2
shows the front faces of test Nos. 5 and 6 which were typical of the mor
tar layers havin g a reduced water/cement ratio. The appa rent irregularities
· on the layer surface were traces left by the trowel during the placement of
the mortar.
3.2 GEOMETRY AND BOUNDARY CONDITIONS OF TESTS
In al l of the tests, the movable block slab surface was in the
same vertica l plane as the front face slabs of the fixed blocks before the
mortar was placed. Therefore the resistance of the layer to the force
3-2
FIGURE 3.1 PRE-TEST SURFACE CRACKS IN TEST NO. l
FIGURE 3.2 APPEARANCE OF SPECIMEN NOS. 5 and 6 IMMEDIATELY BEFORE TESTING
3-3
applied through the movable block could be developed only by the trans
mission of shear and/or adhesive stresses through the mortar layer. The
top and bottom-edges of the mortar layer were aligned with the top and
bottom edges of the movable block. This ensured a one-directional trans
mission of stresses and avoided stress concentrations around sharp geometri
cal transitions.
For the first 10 tests, no restrictions were imposed on the lat
eral boundaries of the layer, and the boundary was provided by the adhesion
strength along the contact of the mortar layer and the concrete surface
slabs of the fixed blocks. For test Nos. 11 to 18, steel plates were used
to press the mortar layer against the fixed walls at specified distances
from the movable block. Lateral boundary conditions were semi-fixed by
the steel plates in these tests. These plates can be seen in Figs . 3.3
and 3.4.
For all tests, except the first two, wetted cotton was used to
fill the 1/2 in. (1.27 cm) gap between the movable block surface slab and
the surrounding surfaces. Filling of this separation presented possible
intrusion of mortar which would result in frictional resistance between
the movable block and fixed wall.
3.3 MAIN VARIABLES AFFECTING THE STRUCTURAL BEHAVIOR OF THE MORTAR LAYER
Once the geometrical condition of the tests was chosen, a set
of layer and "rock-mass" characteristics, which would influence the struc
tural behavior of the layer, were selected and are summarized in Table 3.2.
For a series of tests, different values were given to the particular
3-4
FIGURE 3.3 USE OF 6 X 18 IN. (152 X 457 MM) PLATES IN TEST NOS. 13 AND 14 TO SIMULATE ROCK BOLTING
FIGURE 3.4 USE OF 16 X 24 IN. (406 X 609 MM) PLATES IN TEST NOS. 17 AND 18 TO SIMULATE ROCK BOLTING
3-5
TABLE 3.2
DIMENSIONS OF t,ORTAR LAYER
Test Thickness, no. in. (cm) L*,in. (cm) Remarks
l 1. l (2.79) 24 (60.96)
2 .9 (2.29) 48 (121.92)
3 1.0 (2.54) 48 ( 121. 92)
4 .7 (1. 78) 7 (17 .78)
5 .7 (1. 78) 48 ( 121. 92)
6 48 ( 121. 92)
7 1. l (2.79} 14 (35.56) /
8 .9 (2.29) 18 (45.72)
9 .7 ( 1. 78) 48 (121.92)
10 .8 (2.03) 48 (121.92)
11 .6 ( 1. 52) 6 (15.24) Steel plates 611 x 18 11
12 .6 1.52 6 (15.24) Steel plates 611 x 18 11
13 .7 (1. 78) 6 (15.24) Steel plates 611 x 18 11
(used tape on slabs)
14 .6 ( l . 52 6 (15.24) Steel plates 611 x 18 11
(used tape on slabs)
15 1. l (2.79} 6 (15.24) Steel plates 611 x 18 11
(Mesh reinforcement)
16 1.0 (2.54) 6 (15.24) Steel plates 611 x 18 11
(Mesh reinforcement)
17 .7 ( 1. 79) 2 (5.04) Steel plates 16 11 X 24 11
18 .8 (2.03) 2 (5.04) Steel plates 16 11 X 24 11
* Distance between the edges of the movable block and the lateral boundaries of the layer.
3-6
characteristic under study while the values of the other p?rameters were
kept constant. Differences in the mode of failure and maximum resistance
loads obtained in these tests were used to assess the influence of that
particular property on the overall behavior of the structure.
After a theoretical analysis complemented with a study of the
available literature on shotcrete behavior (Cecil, 1972; Peck, et al.,
1970; Cording, 1974; Cording and Mahar, 1974; Jones and Mahar, 1974; and
Holmgren, 1975) was made, a hypothesis was developed to explain the possi
ble failure mechanisms and the main variables as shown in Fig. 3.5. The
maximum load resisted by the mortar layer depends on its mode of failure.
There were two basic modes of failure predicted for this test series:
(1) diagonal tension failure in the mortar layer; or (2) separation of the
mortar layer from the surface slab. The actual mode of failure depends
on the relative value of the forces F0 and F1, where F0 is the maximum ad
hesive force holding the mortar layer against the fixed walls that could
be developed along the contact area, and F1 is the force required to in
duce a diagonal tension failure in the mortar layer. If F0 is greater than
F1 the first mode of failure, diagonal tension, will occur or, conversely,
if F1 is greater than F0, the second mode of failure, separation of the
mortar layer, will occur. As seen in the diagram the value of F0 depends
on the size of the contact area along which adhesive stresses act together
with the maximum value of adhesive strength between the layer and the slab,
while ~he values of F1 depend on the thickness of the layer together with
the strength of the mortar. It was decided, therefore, to study the in
fluence of these variables on the values of F0 and F1• The variables
3-7
)
-
---
-
-
w I
CX)
Layer thickness
Strength
Surface conditions
Lateral ~ boundary conditions
,, . Strengt
Fl [. ~ - .k I F0 > F1 Diagonal tension failure
I \ Fl >Fa Adhesive failure
Fa [ ~;;~ ~ .
FIGURE 3.5 SCHEMATIC DIAGRAM SHOWING TWO TYPES OF FAILURE MODES
chosen in this study consisted of: (l) lateral boundary conditions of the
layer; (2) the contact surface characteristics; (3) the mortar strength;
(4) the type of reinforcement ' used in the layer; and (5) rate of load ap
plication to the mortar layer.
The mortar layer thickness was intended to be constant throughout
the test series but could not be closely controlled due to the application
method. For each test its value was measured and recorded along the two
critical sections of the layer; between the fixed and movable blocks.
It was believed that the structural behavior of shotcrete layers
is similarly influenced by t he same variables aforementioned, so that the
results of these mortar layer tests were useful in planning the testing pro
gram for the shotcrete layers. The nature of these variables and the dif
ferent values assigned to them during the eighteen tests performed in this
preliminary study are described in the following sections.
3.3.1 LATERAL BOUNDARY CONDITIONS OF THE LAYER
In the cases where no steel plates were used, the lateral boundary
of the mortar layers was determined by its maximum distance away from the
movable block. For the other cases, when a good contact between the steel
plates and the mortar was obtained, the location of these plates determined
the lateral boundaries of the layer. Column 3 in Table 3.2 shows the dis
tance from the contact between the movable and fixed blocks at which the
lateral boundaries of the layer were located . Column 5 of the same table
indicates whether or not steel plates were used to establish these boundaries.
As shown in the aforement i oned table a considerable range of variation, 2 in.
3-9
'
(5.08 cm) to 48 in. (122 cm) was selected for the locations of the lateral
boundaries of the layers. The location of these boundaries was expected
to influence the structural behavior of the layers in as much as this loca
tion controlled the size of the area over which the adhesive strength be
tween the mortar and the surface slab was developed. Even if the adhesive
strength developed within just a few inches of the movable-fixed block con
tact, longer extensions of the mortar layer would have provided a larger
"buffering" zone should shrinkage in the mortar layer have had adverse
effects on the development of the adhesive strength. Shrinkage in the mor
tar (layer) tended to create shear-strains along its contact with the sur
face slab reducing ~nd sometimes destroying any adhesive strength which
could have developed. Longer extensions of the layer were also expected
to provide better restraints to rotations induced in the layer after separa
tion from the surface slabs was started.
3.3.2 CONTACT SURFACE CHARACTERISTICS
Slab surface conditions along the contact area determined to a
major degree the maximum value of the adhesive strength that developed to
hold the mortar layer to the fixed wall when load was transmitted to the
layer through the movable block. As previously mentioned, the maximum value
of the adhesive strength that could be developed along the contact area to
gether with the effective size of this area determined the maximum value of
the force F0 and , therefore, the structural behavior of the layer.
In order to maintain a uniform surface condition for each test,
and particularly for successive tests in which adhesion was not a variable,
3-10
a standard surface treatment was established. After brushing the slab
with an electrically powered wire brush, the roughness of the slab surface
was measured at representative locations with a special device designed
for this purpose. The device and results of the measurements are described
in Appendix B. Mortar was placed after the roughness was measured.
The surface slabs were form-finished on one side and hand troweled
on the other. For most of the tests, the mortar was placed against the
finished side of the slab after it had been roughened. Variations of the
maximum adhesive strength were provided by (1) the use of the rougher,
hand troweled side of the surface slab as the contact surface in the first
two tests or (2) by covering the inner edges of the fixed block with a fila
ment tape in a strip 6 in. (15.2 cm) wide (see test Nos. 13 and 14).
3.3.3 MORTAR STRENGTH
Variations in the strength characteristics were obtained by al
lowing the mortar layer to cure under the same conditions for different
lengths of time. Material properties of the mortar in each test are sum
marized in Table 3.3.
The strength of each mortar layer was estimated by performing
a series of standard compressive and flexural strength tests on cast sam
ples of mortar obtained from each mix and cured under similar conditions
as the mortar on the wall. These strength tests were conducted at the same
time 'as testing of the mortar layer in the model and were used to check dif
ferences in strengths between mortar layers cured for approximately the same
length of time (strength control). Four cylinders 4 in. x 8 in. (10.2 cm x
3-11
'
TABLE 3.3
MATERIAL PROPERTIES OF TEST SPECIMENS
Splitting Compressive Flexural tensile
strength, strength, strength, Young's
Test f' fr, f sp, modulus c' psixl06 no. psi (KP a) psi ( KP a) psi ( KP a) ( KP a) hours
1 6015 ( 41 ,400) 2.5 (1.72 X 107) 168
2 5540 (38,200) 640 (4,410) 168
3 1965 (13,550) 387 (2,670) 48
4 5925 (40,800) 510 (3,510) 450 (3,100) 168
5 5186 (35,800) 660 (4,550) 505 (3,480) 3.0 (1.72 X 107) 168
6 5186 (35,800) 660 (4,550) 505 (3,480) 3.0 (2.07 X 107) 168
7 4775 (32,900) 430 (2,960) 360 (2,480) 2.8 ( 1. 93 X 107) 168
8 4775 ( 32,900) 430 (2,960) 360 (2,480) 2.8 (1.93 X 107) 168
9 385 ( 2,660) 60 413) 0.3 (2.07 X 106) 7
10 385 ( 2,650) 60 413) 0.3 (2. 07 X 106) 7
11 5090 (35,100) 510 (3,520) 410 (2,830) 2.2 (1.52 X 107) 168
12 5090 (35,100) 510 (3,520) 410 (2,830) 2.2 (1.52 X 107) 168
13 5390 (37,200) 585 (4,030) 440 (3,040) 3.7 (2.55 X 107) 168
14 5390 (37,200) 585 (4,030) 440 (3,040) 3.7 (2.55 X 107) 168
15 5630 (38,800) 415 (2,860) 3.2 (2.21 X 107) 168
16 5630 (38,800) 415 (2,860) 3.2 (2.21 X 107) 168
(35,100) 2.2 7 168 17 5090 480 ( 1. 52 X 10 )
18 5090 (35,100) 480 2.2 (1.52 X 107) 168
3-12
• '
20.3 cm), and two rectangular beams 6 in. x 6 in. x 22 in. (15.2 cm x 15.2
cm x 55.9 cm) were tested from each batch. Standard unconfined compres
sion tests were performed on two or three of the cylinders and Brazil
splitting tensile tests were conducted on the remaining cylinders. In
the compression tests load deformations curves were obtained, and were
used to calculate Young's Modulus; see column 5 of Table 3.3.
3.3.4 TYPE OF REINFORCEMENT
In order to investigate the influence of the mortar layer stiff
ness and ductility on its structural behavior, particularly after cracking
in the layer occurred, two of the mortar layers tested were reinforced
with mesh. The reinforcing mesh used in test Nos. 15 and 16 had al in.
(2.54 cm) square pattern, formed with a 0.063 in. (1.06 mm) diameter wire
and was placed close to the outside surface of the layer. The mesh was
pushed against a fresh mortar layer and covered immediately thereafter with
the second layer. The reinforced mortar layer was held against the fixed
walls with a set of steel plates similar to those shown in Fig. 3.3 but
were located 3 ft (91.4 cm) rather than l ft (30.4 cm) away from the mova
ble block.
3.3.5 RATE OF LOAD APPLICATION
It is reasonable to assume from a structural point of view that
the rate at which the load is applied to the layer will have an influence
on the numerical value of forces F0 and F1 in the aforementioned model.
From the geological point of view, the rate of load application is a very
3-13
1
important variable directly related to the 11 stand-up 11 time of the material
surrounding the tunnel . Since the 11 stand-up 11 time of rock in blocky ground
is highly variable, it was decided to run comparative tests at two extreme
rates of loading.
For all the tests except 8 and 10, a 11 slow 11 rate of loading equal
to 2 lbs/sec (8.9 x ,o-3 kN/sec) was used. For test Nos. 8 and 10, the
load was applied rapidly to simulate the instantaneous development of load
on the layer imposed by a rock block whose gravity load was mobilized quick
ly and whose weight exceeded the support capacity of the layer .
3.3.6 THICKNESS OF THE MORTAR LAYER /
For this series of preliminary tests the mortar layer was intended
to have a uniform thickness of 1 in. (2.54 cm). However, due to the place
ment method, it was not possible to control this thickness accurately over
the entire area of the layer. Column 2 in Table 3.2 indicates the average
thickness of the mortar layers obtained from several measurements taken
along the failure planes of the layer.
3.4 LOADING PROCEDURE
Results obtained from the first several tests indicated that it
was pertinent to study the structural behavior of the mortar layer after
the load reached a value equal to the maximum resistance of the layer. For
the first tests, Nos. l through 11, the loading process was performed en
tirely under load control. The electrically controlled ram was set to apply
a maximum load of 10,000 lbs (44.48 kN) over an interval of 5000 sec. The
3-14
maximum displacement for the ram head (1/2 in.) was controlled by attach
ing an electrical contact switch to the dial gage monitoring the displace
ment of the center point of the mortar layer. Once the displ acement reached
1/2 in. (1.27 cm) a contact was made cutting the load immediate ly to zero.
For the other series of tests, Nos. 12 through 18, the loading
proceeded up to a maximum capacity of the layer under load control. Once
this value was reached, however, the load in the ram was immediately cut
off manually and the displacement of the ram head stopped. A small load,
however, due to the back-up pressure in the hydraulic seals remained in the
ram. Further displacements of the ram head were controlled in such a way
that it applied whatever load necessary to advance at a pre-determined dis
placement rate of 0.0025 in./sec (displacement control). Use of this pro
cedure permitted study of the behavior of the layer and measurement of the
resulting loads and displacements once the maximum capacity of the mortar
was reached.
3.5 TEST RESULTS
With the exceptions of test Nos. 5 and 6, no special difficulties
were encountered in testing the mortar layers. Observations and measure
ments in each test were carried out as previously described and no major
equipment or testing problems were encountered. Non-controlla ble, non
measured loads imposed in the mortar layer during ram head alignment for
test Nos. 5 and 6 created a premature separation of the mortar layer from
the surface slab. Results obtained from these tests were plotted but not
used in comparisons with other test results.
3-15
3.5.l MODES OF FAILURE
Of the two basic modes of failure proposed in themodel of Chapter
3, only separation between the mortar layer and the concrete surface slab
was observed in these preliminary tests. The continuous displacement of
the movable block, induced by the load in the ram, produced adhesion stress
in the contact area between the mortar layer and the surface slabs as well
as tension and compression stresses in the mortar layer itself. It was
observed, however, that in all cases the induced adhesion stresses exceeded
the adhesion strength at the contact area before the level of stress in the
layer reached the strength of the mortar. A separation of the mortar layer
from the surface slab started at the movable block and progressed away from
it toward the outer boundaries of the layer. Variations in the structural
behavior of the mortar layer after separation from the surface slab were
observed in different tests. In one case, test No. 4, the size of the con
tact area beyond the movable block was so small that the adhesion failure
occurred almost simultaneously along its length and the layer moved as a
rigid body uniformly outward with the movable block. Figure 3.6 shows a
frontal view of the failed mortar layer; the fact that cracking did not
occur in the mortar layer indicated that the magnitude of the stress in
duced in the layer never exceeded the flexural strength of the mortar.
In most of the cases, the mortar layer, after its initial separa
tion from the surface slab, started acting like a simply supported beam
having a uniformly loaded center section and end supports which continuously
moved apart (see Fig. 3.7). When the separation between the mortar layer
3-16
'
FIGURE 3.6 FRONTAL VIEW OF FAILED MORTAR LAYER WITH NO CRACKS AT THE MOVABLE-FIXED BLOCK CO NTACT
p
FIGURE 3.7 SCHEMATIC VIEW OF SHOTCRETE LAYER DEFLECTION AFTER SEPARATION STARTS
3-17
and the surface slab became long enough, the bending stresses in the layer
exceeded its flexural capacity and two ve r tical cracks appeared in the mor
tar along the contact be tween the movable and fixed blocks. The progres
sive separation of the mortar layer occurred so fast that the cracks ap
peared almost simultaneous ly with the adhesion failure.
In some cases, when steel restraining plates were not placed at
the boundaries of the layer, t he separation of the mortar layer f r om the
surface slab propagated all t he way to the boundaries of the layer as shown
at the right-hand side of t he upper mor tar layer in Fig. 3.8. In other
cases, the separation of the l ayer from the slab propagated on ly to a point
at which the negative moment , i nduced by the res i dual load of t he ram, ,
created bending stresses in the interior surface of the mor tar l ayer which
exceeded the mortar strength. At this point a vertical crack was formed
at the interior surface of the mortar layer.
In the tests where no steel restraining plates were used, the
necessary rigidity against rotation required at the boundaries was pro-
vided by the adhesion fo rce F0 developed in the remaining area of contact
between the mortar and the surface slab. The left-hand side of the upper
mo r tar layer and both sides of the lower layer shown in Fig. 3.8 are examples
of this situation. Except in the tests in which the contact between the
steel plates and t he mo r tar layer was very irregular, the plates provided
a limit to the length of separation between the mortar layer and the fixed
wall (Figs. 3.9 and 3.10) .
In tests carried out with reinforced layers (test Nos . 15 and 16),
or for those in which the steel plates were closely spaced (tes t Nos. 17 and
3-1 8
FIGURE 3.8 MORTAR LAYERS FAILED BY SEPARATION OF MORTAR LAYER FROM THE SURFACE SLAB
FIGURE 3.9 STEEL PLATES PROVIDING RESTRAINT TO ADHESION FAILURE PROPAGATION
3-19
FIGURE 3. l O TOP VIEW OF MORTAR CRACKING PATTERN IN TEST NO. 17
18), a significant residual resistant was present in the layer even after
large displacements. This resistance was produced by an adhesion between
the mortar layer and the concrete slab covering the movable block. Once
this adhesion failure developed, another vertical crack occurred at the
surface and along the center line of the mortar layer and the resistance
of the layer suddenly approached zero. Figure 3.11 shows the three verti
cal cracks in the mortar layer, produced by bending stresses developed
during the loading in test No . 16. The cracks at the contact of the movable
block with the fixed walls, labeled Number 5, appeared immediately after
3-20
FIGURE 3.11 VERTICAL CRACKS IN THE MORTAR LAYER DUE TO BENDING STRESSES DEVELOPED BY LOADING PROCESS IN TEST NO. 16
separation of the mortar layer from the wall; the other crack, along the
center line of the movable block and labeled Number 8, appeared later,
after a considerable displacement of the movable block had taken place.
Figure 3.10 shows a similar adhesion failure and the corresponding crack
pattern, obtained in test No. 17 in which steel plates were used. The
top view of the central zone of the mortar layer in Fig. 3.12 shows clearly
the adhesion failure which developed between the mortar layer and the con
crete slab.
In other cases, such as the case shown in Fig. 3.13 corresponding
3-21
FIGURE 3.l2 TOP VIEW OF ADHESION FAILURE DEVELOPED BETWEEN THE MORTAR LAYER AND THE CONCRETE SLAB COVERING THE MOVABLE BLOCK IN TEST NO. 15
FIGURE 3.13 MORTAR SURFACE CRACKS DEVELOPED ALONG PRE-LOADING WEAKNESS ZONES
3-22
to test No. 2, the cracks in the mortar layer sur.face were not observed at
locations where stresses in the layer were maximum. In these cases, fail
ure occurred along existing cracks produced by shrinkage or relative dis
placement which occurred within the mortar layer shortly after its placement.
The load carrying capacity of the mortar layer after adhesion
failure occurred, decreased rapidly to zero for all the cases in which
steel plates were not used. This was observed independent of the length
of separation between the mortar layer and the fixed walls.
3.5.2 LOAD VS. MOVABLE BLOCK DISPLACEMENT
The mortar layer resistance and the displacement of the movable
block were monitored during the test using an x-y plotter connected to the
ram control system. The unit load, i.e . , the load divided by the 48 in.
(122 cm) of contact between the mortar layer and the fixed walls, was cal
culated and used as a measure of the resistance of the layer. The portion
of the monitored displacements due to deflection of the frame 11 fixed 11 wall
were determined by comparing at equal load levels the magnitude of the plot
ted displacements with those measured by dial gages mounted on the back of
the movable block. The magnitude of these loading system displacements was
subtracted from those measured by the x-y recorder to obtain the net dis
placements of the movable block relative to the fixed wall.
For each of the tests performed, the unit load was plotted on
they axis while its correspondent displacement of the movable block rela
tive to the fixed wall was plotted on the x axis. Figure 3.14 shows three
types of curves, corresponding to three types of structural behavior ob
served in the preliminary tests . 3-23
w I
N -,1:a
+J u "' +J C: 0 u
'+-0
.s::. +J 0) C: QJ .... +J ..... C: :::,
s.. QJ 0.
QJ u C:
"' +J VI .... VI QJ
0:::
Movable block displacements FIGURE 3.14 TYPICAL UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENT
RELATIONSHIPS FOUND IN MORTAR LAYERS
For type No. l and No. 2 curves in Fig. 3. 14 the maximum re
sistance of the layer was obtained as the layer separated from the surface
slab. The initial portion pf the load-displacement curve shows a linear
elastic behavior in which the maximum load is reached at a relatively small
displacement. The type No. l curve shows that once separation occurred the
resistance of the mortar layer dropped sharply to zero. This curve is repre
sentative of the structural behavior of the mortar layer in test Nos. 2
through 10, for which no steel plates or other types of boundary restric
tions were used.
The type 2 solid line shows an instantaneous decline in the applied
load immediately after the ultimate capacity of the layer was reached. The
almost complete reduction of load, required to switch from load to displace
ment control, did not represent an actual reduction of the resistance of the
mortar layer. Once the switch in the control was made, the load in the ram
increased with further displacements of the movable block up to a level rep
resenting the actual residual resistance of the mortar layer at that dis
placement. For further displacements of the movable block the resistance of
the mortar layer decreased at a rate determined by the stiffness of the layer
and the extension of the adhesion failure beyond the movable block. The type
2 dotted line represents the relationship that would have been obtained if
the load in the ram had not been reduced in order to switch from load to
stroke control. The structural behavior of the mortar layer for test Nos.
11 to 17 for which steel plates were used to fix the boundaries of the layer,
are represented by this curve.
The type 3 curve shows the case of test No. 8 in which the maxi
mum resistance of the mortar layer was not reached at the beginning of the
3-25
separation of the layer from the surface slab, but rather in bending with
f urther displacements of the movable block. Curve 3 follows the same path
as curves 1 and 2 up to a point that corresponds to the separation of the
layer from the surface slab; from that point the curve represents the load
deflection curve of a simply supported beam.
The structural behavior of the layers in test Nos. land 2 corre
spond basically with the type l curve. The greater value of maximum load
was the result of the presence of mortar in the gap between the surface
slab covering the movable block and those covering the surrounding fixed
walls.
The relation-ship between the unit-length resistance and movable
block displacements for each of the tests are shown in Figs. 3.15 to 3.23.
The values of the maximum resistance of the layer and the displacement at
which it was obtained together with pertinent remarks for each of the tests
are summarized in Table 3.4. From this table and the aforementioned rela
tionship plotted in Figs. 3.15 to 3.23 the following conclusions can be
drawn:
1. For the layers with load-displacement behavior represented
by type curves l and 2, the magnitude of the displacement
of the movable block at which maximum load was reached has
a maximum value of 0.004 in . (0.102 mm).
2. Residual load capacities equal to 60 to 70 percent of the
maximum capacity were observed in mortar layers whose struc
tural behavior corresponds to that shown by type 2 curves.
This residual capacity was maintained during movable block
3-26
TABLE 3.4
MORTAR TEST RESULTS
Displacement of Maximum carrying the movable block
Test capacity at max load no. lbs ( KP a) in. (cm) Remarks
l 4000 (27,800) .015 (. 0381 )
2 4000 (27,800) .016 (. 0406)
3 1500 ( l O ,340) .005 (.0127)
4 900 ( 6,200) .003 (. 0076)
5 860 ( 5,930) .001 (.0025) Layer was altered during testing set-up.
6 Failed during set-up.
7 5800 (40,000) .005 (.0127)
8 2400 (16,550) .003 ( .0076)
9 450 ( 3, l 00) .001 ( .0025)
10 1000 ( 6,895) .002 (.0051)
11 3240 (22,400) .003 (. 0076) Steel plates
12 1640 (11,600) .004 (.0102) Steel plates
13 1250 ( 8,620) .004 (.0102) Steel plates
14 1170 ( 8,070) .004 (. 0102) Steel plates
15 2500 (17,200) .002 (.0051) Steel plates
16 2300 (15,850) .003 (.0076) Steel plates
17 2850 (19,650) .002 (.0051) Steel plates
18 2600 (17,900) .075 (.1905) Steel pl ates
3-27
Movable block displacement (µm) =
20 0 100 200 300 400 500 600 700 800
100
-----E 16 . C:
......... •,-z:
~w~ ~ ~ -+.> u
l~ca le.~ "' +.> C: 1 ,. 1/0"' 20 in. 0 +-' u 12 C:
0 It- u 0
.s::::. ! 60r /~ ~ "-M-1 L = 24 in . +.> O'l (L - 610 mm) w C:
I . Q.I O'l N ,-. C: 00 ClJ
+.> ,-.
I f'f "-- M-2 L = 48 in. •r- 8 C: +.> (L = 1220 mm) ::, •,-
s.. c:: 40 ::, Q.I a. s..
Q.I Q.I a. u C: Q.I
"' u +.> C: VI 4 "' ,,- +.> 20 VI VI Q.I •r-
0::: VI (IJ
0:::
0 0 ____ ........, ___ ____. ____ ....__ ___ ___._ ___ ......... .._ ___ __._ ____ ..__ ___ _,
0 - --8 12 16 20 4 24 28 32 Movable block displacement (lo-3 in.)
FIGURE 3.15 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
Movable block displacements (µm)
201 0 l 00 200 300 400 500 600 700 800
100 .......... . i::
~16 •r--:z:: 4-.:::L
¥801 ~ l~rta~fscale~
-----.µ u ro .µ S::" 0 lavPr 1o in . u 0
4- 12 u 0 4-
0 .. c. ..c: 60 +'
0, +' w C 0, I QJ i::
N ,-- QJ I.O .µ
.,_,
] I M-3 L = 48 in. i:: 8 ::, r (L = 1220 mm) s... QJ s... 40 0. QJ
0.
I ~/ rM-4 L = 7 in. QJ u QJ (L = 178 nm) i:: u ro i:: .µ ro (/) +'
•r- 4 (/) (/) ·;;; 20 QJ
c::: QJ c:::
0 4 8 12 16 " 20 24 28 32
Movable block displacements (10- 3 in.)
FIGURE 3. 16 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
20r- 0 r I
100
- 16 ...-.. E E '- f 80~
z ~ ---.µ u
"' .µ c:: 0
12 c::
u 0 u
4-0 4-
..c:: 0 6 w .µ ..c I 0) .µ
w s:: 0) 0 a., c::
,-- a., ,--
.µ •,- 8 .µ s:: ,,-:::, § 40 s.. a., s.. c.. a.,
a.,
to~ u c:: "' .µ
4 VI •,-VI a., VI & a: a.,
0:::
0
Movable block displacements {µm)
100 200 300 400 500 600 700
~;;~;;~~~-:~~
/ M-5 L = 48 in. (L = 1220nm)
rM-6 L = 48 in. {L = 1220 nm)
4 8 12 16 · 20 Movable block displacements (l0- 3 in.)
24
FIGURE 3.17 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
28
800
32
Movable block displacements (µm)
20 0 100 200 300 400 500 600 700 800
100 ...--.. . - C
~ 16 .,... .......
z 4--~ ~ - ,.... .µ - 80 u .µ
"' u
I f I L Mortal' layer ~Scal~f .µ n:, - C .µ 0 C 20 in. u 0
12 u 4--0 ! 60~ I I M-7 L = 14 in.
.s:::. ~ (L = 355 mm) .µ w O'l .µ I C O'l
w (l) C ...... ,.... (l) ,.... .µ
I U\ I ~ M-8 L = 18 in . .,... .µ C 8 .,...
(L = 457 mm) ::, C ::,
s... (l) - s... 0. (l)
0. (l) u (l) C u n:, C .µ n:, V) .µ
.,... 4 V) V) .,... (l) V)
ex: (l) ex:
0 o _____ _,o\-______ ...._ ___ ___._ ____ ...._ ___ ____., ____ ..._ ____ i..,_ ___ __,
0 4 8 12 16 20 24 28 32
Movable block displacements (l0- 3 in.)
FIGURE 3. 18 UNIT LENGTH RESISTANCE VS t,OVABLE BLOCK DISPLACEMENTS
Movable block displacements (µm) 20 0 100 200 300 400 500 700 800
,oo~==~=--~--~--r---r--~=--r--1 16 -. - C
~t~ E ! 80~ -z: ~ - cale +-' Mortar laye~ ~ u "' +-' "' C 12 +-' 0 C u 0
u ~ ~ 60 0
w 0 I ..c
w +-' ..c N C') +->
C C')
OJ C ,- OJ
8 ,-
+-' .,... +-> C .§ 401 M-10 L = 48 in. ::::,
s.. / ( L = 1220 mm) OJ s.. c.. OJ - c.. OJ
~ 20 I j\ / u r M-9 L = 48 in. C
"' 4 (L = 1220 mm) +-> Vl +-> .,... Vl Vl .,... OJ Vl
cc: OJ cc:
0 0 0 4 8 12 16 20 24 28 32
Movable block displacements (l0- 3 in.) FIGURE 3. 19 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
- Movable block displacements {µm)
20 0 100 200 300 400 500 600 700 800
100------------,----~------r----,------:r-----,------,
_161--: E C
......... . .... z ......... ..::,t. '+- 80
.0 ,-
.µ --- I L Mortar u tO .µ - .µ u
§12 tO .µ
u c:: 0
'+- u 0 '+- 60 w
I ..c:: 0 w .µ
w O'l ..c:: C .µ
I 1 I M-11 L = 46 i n . w / l / 4 11 St. pl . (l) O'l ,- c:: I (L = 1168 mm) .µ 8 (l)
,-•,-c:: :!: 40 ::::I
c::
I '~ ~ / M- 12 L = 46 in. w / l / 4 11 st. pl . ~ ::::I (l)
(L = 1168 nm) 0.. ~ (l)
(l) 0.. u c:: (l) - i 4 u
VI ~ 20 ..... .µ VI VI (l) .....
e:::: VI (l)
e::::
OL.. 0 0 4 8 12 16 20 24 28 32
Movable block displacements (l0- 3 in.)
FIGURE 3.20 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
-
-20
........ 16 E
" z ..:,,:. __,,
-- .µ u rtl .µ C 0 u 12 4-0
..c
.µ w O'l I C
w Q) .i::,. ,--
.µ •,- 8 C :::,
s.. Q)
0. - Q) u C rtl .µ V1 4 •,-V1 Q) ~
0
-
0 1.25
Movable block displacements (mm)
2.50 3.75 5.00
100--------------~----,..-----r------:r----.-----,
---. C
•,-
" 4-
~ 80 .........
I LMortar layer ~ .µ u rtl .µ 0 l • C 0 u
6 60 ..c .µ O'l C Q)
,--
.µ •,-
C 40 :::,
I rM-13 L = 48 in. W/1/4" St. pl. s.. Q) 0. (L = 1220 mn) Q)
~ (A ~M-14 L = 48 in. w/1/4" St. pl. ...., 20 ...... _ (L = 1220 mn) V1 •,-V1 Q) ~
a.__ ___ ......_ ____ ~-----'-----........_..__ _______ _,__ _________ _ 0 25 50 75 100 125 150 175 200
Movable block displacements (10- 3 in.)
FIGURE 3.21 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
Movable block displacements (mm) 20 0 1.25 2.50 3.75 5.00
100------------------------------------------
-. 16 ........ s:::
E ..... '-
tw~ ~l~ z: .:¥ -+' u
_ Mortar layer ~~a~~~ ltl +' C: 0
12 s:::
<...) 0 u ..... 0 ..... ...,..,... 0 60 ..c: +' ..c: w 0, +'
I s::: O> w Q) s::: (J"1 ,-- Q) I\,,,_ M-15 L = 48 in. w/1/4 11 St. pl. .....
+' r- (L = 1220 mm) ..... 8 +' - C: ..... ~
s.. -,,v\ \ J / M-16 L = 48 in. w/1/4 11 St. pl. Q) s.. c.. Q) (L = 1220 mm) c.. Q) u C1J s::: u
. ltl C: +'
4 ltl
VI t: 20 ..... VI ..... C1J VI
0:: C1J 0::
0 0 25 50 75 100 00
Movable block displacements
FIGURE 3.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
--
-Movable block displacements (mm)
20 0 1.25 2.50 3.75 5.00
100
-E 16 . C:
----.,...
z ----~ '+-......., ..0
.µ .:::, 80 u ,0 .µ I L Mortar 1 ayer .µ u C: ,0 0 .µ
u 12 C: 0
'+- u 0 - ~ ; 60t M-17 L = 48 in. w/1/4" St. pl. .µ Cl ~ (L = 1220 mm) C:
w Q) Cl I
,.... C: w Q)
II \ /- l I / M-18 L = 48 in . O"I .µ ,.... (L - 1220 mm) .,...
8 C: .µ ::,
-~ 40 -- s.. ::, Q) c.. s..
QJ Q) c.. u C: Q) ,0 u .µ C: V) 4 ,0 .,... .µ V) V) Q) .,...
0::: V) Q)
0::
0a 2s 56 ?b 1b'b 1~s 1~0 1~5 2bo
- Movable block displacements (10- 3 in.)
FIGURE 3.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
displacements 15 to 25 times greater than the average re
quired to cause initial failure. Residual capacity of the
layers was reduced to zero at movable block displacements
equal to 1 in. (2.54 mm).
3. The presence of mortar in the gap between the surface slab
covering the movable block and the adjacent slabs increased
the magnitude of the displacements at which maximum-resistance
was achieved by a factor of 4 (0.015 in.).
4. In cases where the ram induced negative moments exceeding the
bending strength of mortar a crack showed up in the interior
surface of the layer; cracks appeared at different distances
from the movable block depending on the thickness of the layer
and the adhesion strength along the mortar-surface slab con
tact. Rock bolts located at distances further away from the
crack would not have had any influence on the resistance of
the layer.
3.5.3 MORTAR LAYER DISPLACEMENTS
GENERAL
As mentioned in Section 2.4, a set of dial gages placed against
the front surface of the mortar layer and attached to the floor was used
to measure the relative forward displacements of the layer with respect
to the floor. The pre-failure displacements measured by these dial gages
for each of the mortar layers tested, are shown in Figs. 3.24 to 3.39.
3-37
M-1
0
50
....... E
w ;::l l 00 ---I w .µ co C
QJ
O 150 E QJ u rd
,--0. Vl 50 .,....
-0
,--rd
~ 100 0 S,...
LL
150
i
6 4 3 2 h Scale ., I 20 in.
Load O
550 lbf (2.2 kN)
1000 lbf (4.4 kN) ~~~:..;-;"";;=;=;;;~i:•;:~~: 1500 lbf (6.7 kN) ~--=:;:.;_-__:_:_:__:-_-_-_-_-_-_:_;.::::::s--: 2000 lbf (8.9 kN) _ 2250 lbf (10.0 kN) -
2500 lbf (11. l kN) 2750 lbf (12.2 kN) 3000 lbf (13.3 kN) 3250 lbf (14.5 kN) 3500 lbf (15.6 kN) 3750 lbf (16:7 kN) 4000 lbf (17.8 kN)
FIGURE 3.24 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
20
40
60 --.o
200
400
600
......... . C .,....
,;:t-I 0 ,..... ..__.,
.µ C QJ E QJ u rd ,..... 0. Vl .,....
-0
,..... rd .µ C 0 s.. u..
M-2 i
_!_. -. --:;.--. ~ -~
cb © ©0 0 0 0 0 0 ~ Scale 20 in. • I
Load 0 Or-500 l bf ( 2 . 2 kN)
1000 lbf (4.4 kN
50 ~ 20 -
C ----E .,....
40 ;:1.
100 I.O .......... I w 0 I I-,-w z .......... I.O LLJ
60 ::::E 150 0 .µ LLJ 0 1500 lbf (6.7 kN) C u (1.) ct:
12000 lbf (8.9 kN) E _J
(1.) CL I I
:!2250 lbf (10.0 kN) 200 u V') I
l'tl ...... 500 • I ,-I . =-----=-----• • 2 500 lb f ( l l. l kN) Cl 0. (./) _J • ~2750 lbf (12.2 kN) .,.... cl:
3000 lbf (13 . 3 kN) 400 -0 ~ 1000 3250 lbf (14.5 ~N) ,-
l'tl a::: 3500 lbf (15.6 kN) .µ LL.
C
3750 lbf (16.7 kN) 600 0 s.. 1500 L I-- 4000 lbf (17.8 kN) LL.
FIGURE 3. 25 FRONT FACE DISPLACEMENT OF LAYER W .T .R . FLOOR
M-3
0
50
.......... w E 100 I
;:!.
~ -0 .µ C: 150 Q) 0 E Q) u ~ ,-0. 500 VI .,.... -0
,-~ 1000 .µ C: 0 s...
LL
1500
i
6 5 6 7 ~ Sca~e • I 20 1n.
.. -
Load 0
__ 250 1 bf ( 1 . 1 kN) - / 500 lbf (2.2 kN __/' ~ 750 lbf (3.3 kN..J--120
l 000 l bf ( 4. 4 kN
40
60 --------------1250 lbf (5.6 kN)
FIGURE 3.26 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
C: .,.... ,;;:J-
I 0 ,-...... .µ C Q)
0 E Q) u ~
200 ~ .,.... -0
400 _e
600
C: 0 s...
LL
M-4
0
50 ,......... E
w ;::1 l 00 I -~ +-> t:: QJ 150 E 0 QJ u r1:l ...... c.. Vl 500 ..... -c ......
r1:l +-> 1000 t:: 0 S-
Lt-
1500
<t.
6 4 3 2 ~ Seale • I 20 in.
Load 0
- 920 lbf (4.1 kN)
500 lbf (2.2 kN) 20
40 To 2030 To 2030
60
FIGURE 3.27 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
,......... . t:: .....
tj" I 0 .... -+-> t:: QJ
n E QJ u r1:l ...... c..
200 Vl ..... -c r-r1:l
400 +-> t:: 0 S-
Lt-
600
M-5 <t.
I •-.7 .- ~-•-• '.,-
6 .12 r Scale • I 20 in.
0 Load
500 lbf (2.2 kN) ..........
5 20 . s:: .,....
--.. E
100 w ;:l.. I ----.i:,.
40
o:::t I 0 ,-
----N +-> s::
150 Q.)
0 E Q.)
u c-s
60
.µ s:: Q.)
E Q.) u c-s ,-
c.. 500 VJ .,....
-0
,-
200 c.. Vl .,....
-0 ,-c-s
+-> 1000 s:: 0 s... u..
,-
400 c-s .µ s:: 0 s... u..
1500 600
FIGURE 3.28 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
M-6 t..
~-~-~
6 @ d) 0) ® ® © © 6 r4 Seale 20 in. ~ l
0 Load 0
,,.....,
20 . 50 s:: .,....
---- ,q-E I ;::l
100 40 0 w ---- ,-I ----~ .µ 'J.) s:: .µ
QJ s:: E 150 60 QJ QJ 0 0 E u 200 lbf (1.2 kN) QJ <tl u ,- ro 0. ,-Vl
200 0. .,.... 500 Vl -0 .,....
-0 -ro ,-.µ
480 ro § 1000 .µ
s:: s.. 0 LJ... s.. LJ...
1500 600
FIGURE 3.29 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
M-7 t
4) l...5) l...6) l7 J lB J l9 J I~ Seale 20 in.
• I 0 ,- ,Load
0 1500 1 bf ( 6. 7 kN
3500 lbf (15.6 ~ -50 ~ I- 5500 lbf (26.5 kN
20 s:::: .... -100 t t tj-
E I ;::1.
40 0
w .__.. r-
I +J ~
I 0 150 t t j60 a I ~
15of ~ ~200 ! r-
lt:l
j 1000~ r 7400 i LL
15001 I __, 600
FIGURE 3.30 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
M-9 i
~-•"• ~-~···· ·
6 © 0 ~ © © cb © © I Seale 4
20 in. . l 0 ,--
200 1bf 0
( 0. 9 kN) -20
. 501- t- ........... "'ti"" / • ----- 300 lbf C: . ....
( 1. 3 kN) -=:t"
E
t I 0
;:1. lOOt 40 ,-w .......... .......... I ~ .µ .µ (J1 C: C:
Q.)
150 60 Q.)
E 0 0 E Q.) QJ u u .,, .,, ,- ,-C. 200 C. V)
500 V) ..... . .... -0 -0 ,- ,-.,, .,, .µ
1000 400 .µ C: C: 0 0 s... s...
LL LL
1500 ' . _600
FIGURE 3.31 FRONT FACE DISPLACEMENT OF LAYER W.R. T. FLOOR
M-11
0
50 --.. E ;:l.
----w .µ 100 I s:: ~ Q)
°' E Q)
150 u 0 10 ,...... 0.. (/)
·r--0 500 ,...... 10
+-> s:: 0 1000· S-
LL
1500
'i.
0 3 4 5 I-. Sca~e • I 20 1n.
Load 0 500 lbf (2.20 kN)
1000 lbf (4.40 kN) 1500 lbf (6.70 kN) 20
2000 lbf (8.90 kN)
2500 lbf (11.10 kN 40 3000 lbf (13.30 kN
60
FIGURE 3.32 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
---. c:: .....
-=::t" I 0 ,...... ----.µ c:: QJ E
0 QJ u ta
,--0.. (/)
200 ..... -0 ,--ta ~
400 c:: 0 s...
LL.
600
M-12 't.
1/4 11 Steel plate Steel plate .....
.12 11 1~ Scale I 20 in. •
0 Load
500 1 bf ( 2. 2 kN) i ·0 1000 lbf (4.4 kN) -
20 .
C: .,.. -E ;::1.
w ---._,.
I
40 0 ,--
I ~
.µ
....... C: (1.) E (1.) 150 u 0 ~
,--a. Vl ,,-
"'C 500 ,--~ .µ C: 1000 0 s..
LL
---1500 lbf (6.7 kN)
]60 ··O i ho ···-r1 r 2000 lbf (8.9 kN)
i jzoo J 870 3576 4150 3673 ,--
400 ~ .µ C: 0 s..
LL
1500 600
FIGURE 3.33 FRONT FACE DISPLACEMENT OF LAYER W.R.T.FLOOR
M- 13 ( l )
0
50
......... w E 100 I ;::I. ~ -co .µ
C: O 150 a, E a, u <l:l ,-a. 500 Vl .....
"'C
.µ C: 1000 0 s..
LL
1500
t
1/4" Steel plate
0 3 4 5
1/4" Steel plate
h Scale .I 20 in.
Load 0
I \ I ~ :::::::-,,• 7 350 lbf (l.60 kN) I
480 lbf (2.~0 kN) 1000 lbf (4.40 kN) 1250 lbf (5.60 kN)
FIGURE 3.34 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
20
40
60
. C: .....
._,.. I 0 ,--
0 t a, E a, u
200 ~ a. Vl
"'C
400 +'
600
C: 0 s..
LL
M-14 (l)
0
50
..--.. E 100 w ;::l
I .......... ~ \.D +-'
C QJ
0 E QJ u 10
,--Cl.. l/l 500 ..... -0
,--10
~ 1000 0 ~
LJ..
1500
0 l/4 11 Steel
plate
2
i
Jl JO
plate
I~ Sca~e 20 ,n.
Load 0
20
40
7 5 0 l b f ( 3 . 3 kN ) 60
1000 lbf (4.4 kN) ll 7 5 l b f ( 5 . 2 kN )
FIGURE 3.35 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
• I
....... . C .....
o:::i-I 0 ,--..........
0 ~
loo j Cl.. l/l ..... -0
400 .--10 .µ C 0 ~
600 LJ..
E ;::l
w -I u, .µ 0 C:
Q) E Q) u ttl ...... 0. Vl ...... " ...... ttl .µ C: 0 s....
LJ...
M-15 (1)
0
50
100
o 150
500
1000
1500
i
1/4" Steel plate Steel plate ~-·~·· ~·-.:.:-
6 { l J l 2J { 3) l 4 h Scale I 20 . •
,n,
Load 0 I -......::::: QiQf 9V :::::--Soo 1 bf (2. 20 kN) I
1000 lbf (4.40 kN) 1500 lbf (6.70 kN) 2000 lbf (8.90 kN) 2500 lbf (11.10 kN
FIGURE 3.36 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
20
40
60 0
. C:
,;:j-1 0 ...... -.µ C: Q) E Q) u ttl ...... 0.
200 -~ " P"'!'" ru .µ
400 §
600
s.... LJ...
M- 16 ( l ) i
1/4 11 Steel plate 1/4 11 Steel plate z:s. ,;;:; .... • e cf
c5 11) (IO) (q) (8) ( ) r4 Seale ~ I 20 in.
0 0 500 lbf (2.2 kN)
50 .......... E
1000 lbf (4.4 kN) . 15 00 l bf ( 6 . 7 kN ) j 2 0 i:::
2000 lbf (8.9 kN) .,....
o:::r I
;::l.
ioo ~
w 40 0 ,...... ~
I .µ tTI i::: __, a,
E a, u 0 r!j
.µ i:::
60 _ 0 a, E a, u - ,......
a. r!j ,......
V) ..... 500 -0
200 ~ ..... -0 ,......
r!j .µ i:::
1000 0 ~
LL..
,...... r!j
400 +' i::: 0 ~
LI..
1500 600
FIGURE 3.37 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
M- 17 ( 1 )
0
50 ,,-... E ;::1.
w ......... 100
I .µ u, s:: N
~ Q) 0
150 u r0 -0. Vl .,.... 500 "'CJ
,--r0 .µ
§ 1000 ~
LL
1500
i
1/4 11 Steel plate
6 4
1/4 11 Steel plate
Load 350 lbf (1.6 kN)
1000 lbf (4.4 kN) 1500 lbf (6.7 kN) 2000 lbf (8.9 kN)
h Sea le I 20 in. "
,a
2500 1 bf ( 11. 1 kN) ~20
40
,,-...
s:: .,.... tj-
I 0 ,--......... .µ s:: Q)
60 _o E Q) u r0
,--0.
200 -~ "'CJ
,--r0
400 t 0 ~
LL
600
FIGURE 3.38 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
M-18 (l)
--0
50
......... E 100 ;::1. w -----I
u, +,) w C: (1) O 150 E (1) u - re ,-0.
500 C/l •r-"'C
,-rt:$
+,) 1000 C: 0 s..
LL.
1500
t.
1/4 11 Steel plate _ II I I ,- 1/4 11 Steel plate h-lP· h · ·· · 8 J
11) no) (9) (X) (X ) ~ Seale .. ( 20 in.
Load
430 lbf (l.90 kN)
1000 lbf (4.40 kN)
1500 lbf (6.70 kN)
FIGURE 3.39 FRONT FACE DISPLACEMENT OF LAYER W.R.T. FLOOR
0
7 20·
40
60 0
. C:
•r-
'<:t" I 0
+,)
C: (1)
E (1)
u re ,-
200 ~ •r-"'C
"400 i
600
C: 0 s..
LL.
The post-failure displacements of the layers having a structural behavior
similar to curve 2 in Fig. 3.14 are shown in Figs. 3.40 to 3.45.
The upper part of the figures show a schematic view looking
down on the mortar layer and the covered fixed wall and movable blocks.
The positions of the frontal dial gages monitoring the mortar layer dis
placements are also shown. The displacements recorded by each one of the
dial gages at every load increment dur1ng the loading process are plotted
in the figure, directly beneath the gage. A displacement profile of the
front face of the mortar layer during the loading process was obtained by
joining with a line the displacements measured in all the gages at the
same load increment. ' The magnitude of the total load on the mortar layer
at every load increment is shown at the right side of the displacement
profile.
DISPLACEMENT PROFILE CHARACTERISTICS BEFORE INITIAL FAILURE
The characteristics of the displacement profile, before initial
failure occurred, were very similar for all the tests. Initially, equal
increments of load corresponded with equal increments of displacement of
the front face of the mortar layer. There was an elastic relationship
between the forward displacements of the mortar layer and the load in the
jack.
The magnitude of the forward displacements was slightly greater
along the vertical center line of the mortar layer, and decreased slightly
away from the center line. The rate at which this value decreased with
distance depended mainly on the stiffness of the contact between the mortar
layer and the surface slabs on the fixed walls. It also depended on the
3-54
;
-
0 ,--
,w · ·, -g: . ~ ..._,,
+.)
~ 0.5 Q,J u ,0 ,.... 0. VI .,.... .,,...
"'O
'; 1.0 +,) s::: 0 ~
LL
I
1.5
M- 13 (2)
I
l/4 in. steel plate
Ci_
I
.......... ,,
FIGURE 3.40 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
~4
Scale .,J 10 in.
1/4 in. steel plate
Load
860 lbf (3.8kN) 830 lbf (3.7kN
800 lbf ~3.6 kN~ 700 lbf 3.1 kN 650 lbf (2.9 kN) 560 lbf (2.9 kN) 510 lbf (2.3 kN 480 l bf ( 2. l kN 415 lbf (1.8 kN) 340 lbf (1.5 kN) 181 l bf ( 0. 8 kN)
I
0
200
400
,,....... . s::: .,....
M I 0 ,---+,) s::: QJ E QJ u rtS
,--0. VI .,....
"'O
,--rtS
+.)
C: 0 ~
LL
,,,._
or W ..-...
Ji i m-
~ 2.50 cu E cu u
'° ..... c.. Ill ..... -0
,- 5.00
'° .µ C: 0 s..
&..
7. 50 I-
-
M-14 (2)
l / 4 in. steel II plate
1
~ @ ..__,,
L \
~
I I
..__,,
I
..__,, ..__,,
I
1• Scale ...I l O in.
\ 1/4 in. steel plate
..__,, Load
0
.---. 550 lbf (2.4 kN)
s::: •,-
C"")
I
100 ~ .......... .µ
580 lbf (2.6 kN) C:
~ Q) u ro ,-c..
200 Ill •,-"'C
465 lbf (2.1 kN) ,-ro .µ C: 0 s..
LL
_J 300
FIGURE 3.41 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
-M-15 (2)
- -0,-
w I .........
c.n ~ -...J ._...
.µ l O C (1)
E (1) u .,, ,-0.. V) .....
"'Cl
20 .... .,, .µ C 0 ~
l.J..
30~ L
-
1/4 in. steel plate
- -
'\.
4-1 I
- - -
------- ,,,,,,. -- / /
//
/ / /
/ // // /
,, / I ,,"' / I
/ / / /
/ I / I
/ / / I
/ I / I
/ I
I I
/ /
I
FIGURE 3.42 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
I• Scale ►~ l O in.
in. steel plate
- Load
· 2500 lbf (11.7 kN)
460 lbf (2.0 kN)
1400 lbf (6.2 kN)
0 ......... .
C: ..... ('Y')
I 0 ,--200 ...., C: (1)
E (1) u .,, ,-c.. V)
•,-400 -o
,-.,, .µ C: 0 ~
l.J..
~600 970 lbf (4.3 kN)
--M-16 (2)
,_,,.
0 --
w -1 E u, E CX> ..__...
.µ
~ 0.5 E Q) u rt! ,-0. V) .,.... -0
.-- l 0 rt! • ,.. .µ c:: 0 S-
LL.
1.sL L
-
l / 4 in . steel plate
"-
~
I I
• /
~•Scale .,J l O in.
in. steel pl ate
-Load
LJ'tV IUI \ I V • 't 11.1,
1400 lbf (6.2 kN)
0 -. C: -~
CV)
I 0 ,-
20 ..__... .µ s::: (1)
~ u ttJ ,-0. VI
40 .,.... -0
,-
"' .µ c:: 0 S-
LL.
~ 700 l bf ( 3. l kN) J6o
FIGURE 3.43 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
--M-17 ( 2)
.,... or ----w -E I
c.n -I.O .,._,
1- C 5 QJ
&l u ,0 ,-a.
·VI .,.. -0 ,.... 10 rel ,µ C 0 s..
LL.
15~ L
--
1/4 in. steel plate
r: 't..
..
f---Sc~_ ···--i 10 in.
in. steel plate
Load
2880 lbf (12.8 kN)
1680 lbf (7.5 kN)
1770 lbf (7.9 kN)
0
200
400
.......1600
FIGURE 3.44 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
----. C ,,-
CV)
I 0
,µ C (l)
E (l) u rel ,-0.. VI .,....
"O
,--rel ,µ C 0 s..
LL.
-
-
w
!sl --- I 0)
0
QJ
~ u ,0
----,-0. V) .,...
"C
,_ 10 ,0
-+-> C: 0 s.. I LL
15l-
--1
M-18 (2) Ct
I ~S~ a 1 e _ ··-i 10 in .
1 / 4 in • s tee 1 plate
1/4 in. steel plate
Load 0
1700 lbf (7.6 kN) I ----.
L ~ 2170 lbf (9.7 kN) J 200 i
\ -----1 -+-> 2000 lbf (8.9 kN) s::::
QJ --------- E QJ
1900 lbf (8 . 5 kN) u tO - - ,--- 400 ~ ---- .,... -- "C
I I tO -+-> C: 0 s..
LL
L _J 600
FIGURE 3.45 FRONT FACE DISPLACEMENT WITH RESPECT TO THE FLOOR
relative stiffness of the layer with respect to the movable block and on
its length. For example, in test Nos . 4 and 7 which had relatively stiffer
layers extending for smaller 'distances -, 7 in. (17.8 cm) and 14 in. (35.6
cm) respectively, away from the movable block, the forward displacements
along the layer were more uniform than in the other tests.
In some cases where mortar was present in the slot surrounding
the movable block (test Nos. 1 and 2), the magnitude of the forward dis
placements of the mortar layer at failure was 3 to 4 times greater than
the average value obtained in the other tests and the shape of the dis
placement profile was less pronounced.
DISPLACEMENT PROFILE CHARACTERISTICS AFTER FAILURE
The post-failure displacements of the mortar layers in which the
structural behavior is represented by curve l in Fig. 3.14 occurred very
rapidly and couldn 1 t be measured. For mortar layers having load-deflections
similar to curves 2 and 3 these displacements show a shape very similar to
the deflection curve obtained for a simply supported beam with a centered
uniformly distributed load. The forward displacements of the layer have
a maximum value along the section covering the movable block and gradually
reduce to zero at the points where the steel plates were located, except
in test Nos. 11 and 12 where the adhesion failure propagated beyond the
plates.
The rate of decrease in these displacements away from the movable
block depends mainly on the stiffness of the layer and the distance between
the steel plates. As expected, the post-failure displacements for the mor
tar layers which are represented by curve 3 in Fig. 3.14, test No. 17, are
3-61
• !
similar to those obtained in the other tests. For all tests, the general
pattern and the values of the forward displacements of the mortar layers
before and after failure, corresponds very closely to the structural be
haviors described in the preceding section.
3.5.4 STRAINS INDUCED IN THE MORTAR LAYER DURING THE LOADING PROCESS
Whittemore Points were placed on the outside surface of the mor
tar layer to monitor longitudinal _strains during the loading process.
Figures 3.46 to 3.53 show a top view of the fixed walls, the movable block,
the mortar layer and the position of the Whittemore Points. The direction
of the strains along the mortar layer surface during the loading process,
determined by the relative displacement of the Whittemore Points with re
spect to each other, is shown in the lower part of the figure. In most of
the tests a zone of tensile strain was created in the outside surface of
the mortary layer covering the movable block and its surroundings. Compres
sion strains were observed in zones away from the movable block.
This state of strain in the outside surface of the mortar layer
corresponds exactly with the state of strain that should develop to fit the
structural behavior (profile displacements) described in previous sections.
In some cases compressive strains were measured along the full length of the
mortar layer (test Nos. 11 and 17) while on others both compressive and ten
sile strains occurred on the mortar covering the movable block (test Nos. 9
and 13). These differences in strain distribution resulted from large dis
tances between adjacent Whittemore Points. The Whittemore Points were lo
cated in such a way that part of the mortar layer surface between them was
3-62
w I
O"I w
M-1 ct 11? i n
11_.~
l I L I C:. Max strain +0.002 in. I I
{between 5-6l = = ~, -1 2 3 4 5 6 7
I· Comp. + Tens. +Comp4
M-2 <t.
I Max strain +0.0066 in. ( 3-4) ....... WWW - - - t.J ] - - - WWW I
lA 18 1 2
Comp.
3 4 5 6 7 8
.. I JensJ JensJ JensJ fonip_.l. Points Lost
9
Tens. = Tensile Comp. = Compression
FIGURE 3.46 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I
°' ~ I
M-3
Max strain +0.0004 in. (between 5-6) - r\
-3 4
Tens. Comp. Tens. Comp. ~
M-4
Max. strain -0.0003 i::i(between 5-6) ~
-
i
I
Tens.
't
I
No l'lO
strair .
6 5 l 4 2 3
Comp . l Comp . . . ~ .
-9 0
No l'W
Comp. s trai r
FIGURE 3.47 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
I ] o i !1J·
I Tens. = Tensile Comp.= Compression
M-5 i
[ I I ] Max. strain +0.0001 in] - • - ~-:!: W W WWW
,,.o i ~1
2 3 4 5 6 7 8 9
I· No strain ·I· Tens. • 1~t~~i~ M-6 i
w
i I
I O'\
L I Max. strain l (.J1
& m N C, +0.0008 in.~
• ...a m a l 2 3 4 5 6 7 8 9
~ No strain • 1·
Tens. + Comp. ~ Tens. = Tensile
Comp. = Compression
FIGURE 3.48 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I
m m
I
[
M-7 i
1 J:Max. strain +0.0005 in.
I
I I - a:..: yr - :a 2 3 4, 5
~ Tens. ~ M-9 't
Max._ strain •:.oO~~i .1 J ··- - ,-,, • ,., J l 2 3 4 5 6 7
~ No
Tens. Comp. strair Comp.
Tens. = Tensile Comp= Compression
FIGURE 3.49 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I
0)
--..J
M-11 i
-L _,l ... J. I I Max. strain z:S2 • • -0; 00~5 2 n .
4 ...... •• µg;
,,.a i ri•i
2 3 4 5 6 7
~ Comp. +ComP,·!$om~Jom~.Com~ up to up t crack crack
M-12 no strain<t_ tens. afterward! afterwards
I I-Max. strain +o •. o:s in:\t --~ J av • >
14 13 12 11 10 9 8
~t~~i nl ri Tens. ~ Tens. = Tensile Comp. = Compression
FIGURE 3.50 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I
O')
00
M-13
I C ... • u -No
~ train
2
i
L ;l ,. J ~:;:· ~train -0.0006 in] 10 in J I• p
3 4 5 6 7
Tens. Comp. Comp. up to crack tens. afterwards
M-14 <t
i Max. strain +0.0022
14
in;) 13 .- ~
l "' - as •=
11 10 9 8
Tens._l No strainlTens.lTens. up to crack comp. afterwards Tens.= Tensile
Comp.= Compression
FIGURE 3.51 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I 0)
\.0
M-15 i
I
[
- I .
M-16
•
t ] ,ax. strain +0.0006 in. I ... I ... .. ~ -l 2 3 4 5 6 7
~Comp+ Tens. +Campi
i
-<G __ L .1.J:::x._s_t:: ::022 in. I
l 2
Tens. I Comp. up tolup to crack crack
3 4
Tens.
comp. tens. afterwards afterwards
5 6
Comp.
7
Tens.= Tensile Comp.= Compression
FIGURE 3.52 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTENSOMETER
w I
--..J 0
M-17 i I 1,0 ; ~~
~1 [_ _ l J::train -0~004 in~J _r~ - --~ __. ""'wF WWW
I
2 3
L Comp. J M-18 Ct
Max. str:i: _0.0009 in . . E t l :.ws -2 3
Tens.~Comp. r • •
,,, .I
Tens. = Tensile
Comp.= Compression
FIGURE 3.53 STRAIN DISTRIBUTION ON FRONT FACE OF THE MORTAR LAYER MEASURED BY WHITTEMORE EXTNESOMETER
subjected to compressive strains while the rest was under tensile strains,
so that the relative displacement measured between the two points was the
resultant of the two opposite strains. Reducing the distance between adja
cent Whittemore Points would lead to a more realistic measurement of the
distribution of strains in the surface of the layer.
3.6 SIGNIFICANCE OF VARIABLES
Each one of the 18 performed tests was planned in order to show
the importance of a particular variable in controlling the structural be
havior of the layer. During a pair of tests all variables, except one,
were kept as constant as possible. Table 3.5 indicates which tests were
used to compare the effects of each chosen variable. The table contains
eighteen rows and columns corresponding to a specific test. The variable
studied is shown in the table at the location given by the tests carried
out for its comparison. For example, test Nos. 1 and ·2 were carried out
to determine the influence of the length of the mortar layer relative to
the edge of the movable block on its structural behavior.
The importance of each variable will be discussed based on its
effect in controlling the maximum and residual resistances of the mortar
layer. The structural test results are discussed as follows.
3.6.1 LATERAL BOUNDARY CONDITIONS OF THE LAYER
A great number of tests (Nos. 1, 2, 4, 7, 11, 12, 17 and 18) were
performed to establish the importance of this variable. The analysis and
discussion of the results were divided into groups according to the
3-71
TABLE 3.5
VARIABLES COMPARED BETWEEN TESTS
Test no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1 2 L 3
4 5 L 6 L 7 M L
w 8 Lo I
--..J 9 M M M M N
10 Lo 11 S-8 12 S-8 13 s s 14 s s 15 Re Re 16 Re Re 17 S-4 S-4 18 S-4 S-4
LEGEND: s = Surface conditions Lo = Load rate Re = Reinforcement S-8 = Steel plates 8' apart L = Length of the mortar layer S-4 = Steel plates 4' apart
relative to the edge of the M = Mortar strength movable block.
structural behavior of the layers described in Section 3.6. The differ
ence between these structural behaviors was dependent on whether or not
steel plates were used as boundaries of the mortar layer.
Figure 3.54 shows the resistance-displacement relationship for
test Nos. l, 2, 4 and 7 in which the layer exhibited a structural behavior
corresponding to the type l curve in Fig. 3.14. The slight deviation from
this pattern shown by test Nos. l and 2 was caused by presence of mortar
in the slots between the surface slabs. The higher value of the maximum
layer resistance per unit length of contact, 105 lbs/in. (19 kn/m) was ob
tained in test No. 7 for a mortar layer extending 14 in. (35.5 cm) away
from the movable block. A similar value (61 lbs/in.) was obtained on test
Nos. l and 2 where the edge of the mortar layer was located 24 in. (61 cm)
and 48 in. (122 cm) away from the movable block, respectively. The lower
value of the maximum resistance was obtained in test No. 4 in which the
mortar layer extended only 7 in. (17.8 cm) away from the movable block .
It could be concluded from these tests that in the absence of
boundaries the length of the mortar layer beyond the movable block only
affects the maximum resistance of the layer. In addition, the length of
the mortar layer beyond a certain distance, between 7 in. (17.8 cm) and
14 in. (35.5 cm) for these cases, did not have any influence on the struc
tural behavior nor support capacity of the layer. The relatively small
magnitude of this limiting distance indicates that the distribution of ad
hesive stress between the mortar layer and the surface slab, is restricted
to relatively narrow bands on each side of the movable block. However,
the actual width of these bands does not necessarily range between 7 and
3-73
Movable block displacements (mm)
20 0 100 200 300 400 500 600 700 800
100 .........
c:: .- 16 .,_
'-E ..... '- ..ci. z ~
.--__. ------ao .µ .µ u u re, re, .µ .µ c:: c:: 0
12 0
u u ..... ..... 0 0 60
..c ..c w .µ .µ
I Ol Ol '-I c:: c:: ..i::,. Q.) Q.)
.-- .--.µ
8 .µ
•,- •,-c:: c:: ::::i ::::i40H r; I M-7 s... s... Q.) Q.) C. C.
Q.) u c:: ro .µ 4 Vl ·r-Vl I Vl Q.) Q.)
a:: a::
0 00 4 8 12 16 20 28 2
Movable block displacements (lo- 3 in.)
FIGURE 3.54 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
14 in., as suggested by the above test results , since independent tests
indicate that the lower value obtained in test 4 may have been caused by
shrinkage rather than by limiting the actual length over whic h adhesion
could be developed. Thus the actual length over which the adhesion stress
is distributed may be less than 7 in . (17.8 cm).
The resistance-displacement relationships for test Nos. 11, 12,
17 and 18 are shown in Fig. 3.55. Three of the tests, Nos. 11, 12 and 17.
have a similar structural behavior corresponding to the type 2 curve in
Fig. 3.1 4. In the other test the layer behavior is similar to that ex
hibited by the type 3 curve. The maximum resistance of the layer for test
Nos. 11, 12 and 17 varied between 30 lbs/in. (5.5 kN/m) and 60 lbs/in.
(11 kN/m) and was independent of the relative position of the steel plates
with respect to the movable block.
The locat ion of the steel plates closer to the movable block in
test No. 17 increased the level of the residual resistance of this mortar
layer to twice the value obtained in test Nos. 11 and 12. In addition,
this r esidual resistance was maintained for displacements approximately
twice those shown in test Nos. 11 and 12, giving more ductility to the
layer .
The mortar layer in test No. 18 had a res istance in bending that
was greater than the resistance in adhesion. The high resistance of the
layer when behaving as a beam is attributed to the location of the steel
plates in close proximity to the movable block.
3-75
Movable block displacements (mm)
20r-- 0 0.5 1.0 1. 5 2.0 2.5 3.0 3.5 4.0 I I I
100
.--.. . .--.. 16 C:
•,-E ......_ ......_ '+-z: ..0 .:.t. ,-..__.. ..__.. 80 .µ .µ u u ~ ~ .µ .µ C: C:
8 12 0 u
'+- '+-0 0 60
..c ..c 1/11\ M-18 .µ .µ w en en I C: C:
......i QJ QJ (J') ,- ,-
.µ 8 .µ •,- •,-C: C: :::,
: 40 nrT ~ s.. / ........ M-17 - -QJ QJ 0. 0.
QJ QJ u u C: C: ~ ~ .µ
4 .µ 1/l -~ 20 •,-1/l 1/l QJ QJ
c::: c:::
0 20 40 60 80 100 120 140 160
Movable block displacements (10- 3 in.)
FIGURE 3.55 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
3.6.2 SLABS SURFACE CHARACTERISTICS
Test Nos. 13 and 14 ~ere performed with mortar layers similar to
the ones used in test Nos. 11 and 12 except that in test Nos. 13 and 14
filament tape was used to reduce the adhesive strength between the mortar
and the surface slabs along 6-in. (15.2-cm) vertical bands on either side
of and adjacent to the movable block.
The resistance-displacement relationships for tests Nos. 11, 12,
13 and 14 are shown in Fig. 3.56. All tests showed a similar structural
behavior corresponding to the type 2 curve in Fig. 3.14.
The mortar layers in test Nos. 13 and 14 had approximately the
same value, 22 lbs/in. (4 kN/m}, of maximum resistance. Higher values of
the maximum layer resistance, 30 to 60 lbs/in. (7 to 11 kN/m), were obtained
in test Nos. 11 and 12. No differences were observed in the level of the
residual resistance of the layers, but shorter displacements of the movable
block were required to reduce completely the residual resistance of layers
11 and 12.
As indicated in these tests a direct relationship exists between
the adhesive strength acting along the mortar layer-surface slab contact
and the value of the maximum resistance of the layer. The variation of
this adhesive strength does not show any influence on the residual resist
ance value. The higher rate of reduction for the residual resistance with
respect to the movable block displacements, was caused by the poor constraint
offered by the steel plates in test Nos. 11 and 12.
3-77
Movable block displacements (mm) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 I I I I I I I I I
,......20 --. E s:: '- .,.... 5.0 z: '-~ i+- 100 .__.. ..0
,--.µ .__.. u i 16 .µ
u s:: ~ I 4.0 0 u C 8Q
0 4- u 0
4-
-512 0
en ..r::::. 3. 01-r ---- M-11 s:: 61 601 a.,
,-- s:: a.,
w .µ ,-- (./) UI ---- _M-12 I .,.... c.. -...J s:: .µ .,.... 00 ::, 8 .,.... ~
C s... ::, .. 2. QIU, / ,.-M-13 a., 40 -0 c.. s... ,,:s
a., 0 a., c.. ....J llr' / ,-- M-14 u s:: a., ,,:s u .µ 4 C (./) ,,:s .,.... .µ 20 (./) (./) a., .,....
c:::: (./) a.,
c::::
Ql_ 0 - 20 40 60 80 100 120 140 160 Movable block displacements (10- 3 in.)
FIGURE 3. 56 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
3.6.3 MORTAR STRENGTH
The mortar strength of the layers used in test Nos. 3, 7 and 9
was successively reduced, see Table 3.3, by decreasing the time of curing.
As seen in Fig. 3.57, the resistance-displacement relationships
for these tests are similar to that shown by type l curve in Fig. 3.14.
The highest value of the maximum unit resistance was obtained in
test No. 7 and decreased successively for test Nos. 3 and 9. These results
indicate that the strength of the mortar in the layer directly affects its
maximum unit resistance. This is expected since the adhesive strength of
the mortar layer depends in part on the time of curing.
3.6.4 USE OF REINFORCEMENT (IN THE MORTAR LAYER)
Test Nos. 11, 12, 15 and 16 were performed in order to determine
the effect of mesh reinforcement on the structural beh~vior of the layer.
As seen in Fig. 3.58 the structural behavior of the layers in
these tests is similar to that shown by the type 2 curve in Fig. 3.14. The
maximum unit resistance is very close for test Nos. 11, 15 and 16 and has
an average value of 50 lbs/ft (9 kN/m). The lowest value of this resistance,
in test No. 12, was probably caused by pre-test cracking of the mortar layer.
The tests indicate that there is no significant difference in maximum re
sistance of mortar layers with or without reinforcement.
A considerable difference exists, however, in the residual resist
ance of the reinforced and non-reinforced mortar layers. The reinforced
layers exhibit higher residual resistance and lower rates of reduction of
this resistance with displacement of the movable block. The reinforcement
3-79
Movable block displacements (µm)
0 100 200 300 400 500 600 700 800
I I I I I I I 20 r-- ......... .
I s:: 5.0 E •r-
'- ~ 100 z .:,,,'_ ..0 ,......
..µ 16 ----u ..µ res u
801 4.0 ..µ res
s:: ..µ 0 s:: u 0
u 4-0
12 ~ H 0 c.. .s::::.
:5 6 ~3.0 ..µ O>
O> o -o I s:: I I .--M-7 aJ s:: res ,...... aJ 0 ,...... _J
..µ w •r-
8 ..µ
I s:: •r-co ~ s:: 40L 2.01-f r ,_M-3 0 ~
s.... aJ s.... c.. aJ
c.. aJ
20L 1.0 I / / I ,........... u aJ ~M-9 s:: u
t'CS 4 s:: ..µ res V) ..µ
•r- V) V) •r-aJ V)
c:::: aJ c::::
0 0 4 8 12 16 20 24, 28 32
Movable blnck displacements (l0- 3 in.)
FIGURE 3.57 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
Movable block displacements (mm)
0 0.5 l. 0 l . 5 2.0 2.5 3.0 3.5 4.0
201~
I I I I I -----E
-----z: .::,,:_ l 00 ..0
...--+-> u rt) 16 +->
+-> u s::: rt)
so1 0 +-> 4. u s::: 0
4- u 0
4-.s::: 0 +-> 12 Ol .s::: s::: +->
601 3. Q) Ol ,- s:::
QJ
+-> ,-•r-
40~ i s::: +-> w :::i •r-
8 s::: I s... :::i co Q)
---' c.. s... Q)
QJ c.. u s::: Q)
ro u +-> s::: Vl 4 rt)
20L- l. •r- +-> Vl Vl Q) •r-
0::: QJ 0:::
0 0 - 0 l'.'.U 40 bU ~u
Movable block displacements
FIGURE 3.58 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
controls the residual resistance of the layers since it increases their
stiffness and ductility. The maximum resistance offered by the reinforced
layer may develop after separation from the surface slab if the reinforce
ment increases the moment capacity of the layer to a level above its ad
hesion strength.
3.6.5 RATE OF LOADING
Two sets of tests carried out with 3-day old layers (Nos. 7 and 8)
and 7-hour old layers (Nos. 9 and 10), were used to determine the influence
of the rate of loading on the structural behavior of the layer. The struc
tural behavior of al1 the tests was very similar to that shown by the type 1
curve in Fig. 3.14.
For test Nos. 7 and 8 the maximum resistance of the mortar layers
were 110 lbs/ft (19 kN/m) and 50 lbs/ft (9 kN/m), respectively, the higher
one corresponding to test No. 7 performed with the smaller rate of loading
2 lbs/sec (8.9 x 10-3 kN/sec).
For the other set of tests, Nos. 9 and 10, the maximum resistances
of the mortar layers were 22 lbs/ft (4 kN/m) and 5 lbs/ft (2 kN/m) respectively.
The higher value was obtained for test No. 10, in which the layer was loaded
with the maximum rate of loading, equivalent to an impact load. The incon
sistent differences shown by these results indicate that changes in the
rate of loading do not have a systematic influence in the structural be-
havior of the mortar layers or in the values of the maximum resistance.
3-82
3.6.6 THICKNESS OF THE LAYER
As previously explained, the same thickness of the mortar layer
was used for all tests in this preliminary program, therefore no special
tests were conducted to investigate its influence on the structural be
havior of the layer. The small variation of this value (3/4 to 1-1/2 in.)
between the mortar layers made it impossible to determine the effect of
thickness on the structural behavior of the layer. However, from the same
results obtained from these tests and knowledge of the structural behavior
of uniformly loaded beams, it can be concluded that the residual resistance
of the layers which follow type 2 and 3 curves, is directly proportional
to the third power of its thickness.
The influence of the mortar thickness on the maximum resistance
of the la}~r could not be established since all of the mortar layers ex
hibited the same mode of failure (adhesion).
3.7 CONCLUSIONS
3.7.l PERFORMANCE OF THE TESTING DEVICE
The performance of the test device was checked by careful ob
servation of the behavior of the apparatus and its effect on test results.
For example, in the first two tests mortar penetrated the slots surrounding
the movable block and thus altered the structural behavior and capacity of
the layer. It was decided, for future tests, to prevent penetration of
mortar in to these slots so that only the surface conditions and strength of
the mortar would be tested. This was accomplished by filling the slots with
3-83
a low frictional material such as cotton or a caulking compound. It was
also observed during these first two tests that the surface slabs were
displacing with respect to the fixed walls in a zone close to the movable
block. Additional bars tying these concrete slabs to the fixed walls were
provided to prevent this movement.
Forward movement of the fixed walls was monitored with dial gages
as explained in Section 2.4. After the first three tests additional pre
stress forces were applied to the fixed walls, reducing their forward move
ment to a negligible level.
After minor adjustments during the first few tests the device was
found to perform satisfactorily. The friction forces on the movable block
were less than 50 lbs (222.5 x 10-3 kN) when the block was displaced with
out a mortar layer present. There was no appreciable tilting or rctation
of the movable block and the rams used to apply the loads could be controlled
with sufficient accuracy.
3.7.2 SUMMARY OF THE EFFECTS OF THE VARIABLES ON THE STRUCTURAL BEHAVIOR OF THE LAYER
The same mode of failure--separation of the mortar layer from the
surface slabs--was present in all the tests carried out in this preliminary
program.
Two typical structural behaviors were observed for the mortar
layers tested. In both, a very stiff, elastic relationship existed be
tween the resistance of the layer and the displacements of the movable
block, before the maximum, or peak, resistance of the layer was reached.
3-84
However, for further displacements the resistance of the mortar layer in
one case dropped immediately to zero. This occurred in short layers and
layers not having boundaries ·and sufficient adhesion to provide end re
straint and development of a simply supported beam. In the other case,
the resistance of the mortar layer was gradually reduced with further dis
placement of the movable block. The post-maximum resistance offered by
the mortar layer has been called residual resistance.
The structural behavior of the mortar layers tested in this pre
liminary program was controlled by the lateral boundaries of the layer.
Whenever steel plates were used in the tests, a boundary to the adhesive
failure propagation was created, thus enabling the layer to behave as a
simply supported beam and to provide some residual resistance. When no
steel plates were used, the adhesive failure propagated in most cases to
the layer boundaries, producing an instantaneous failure.
The maximum resistance of the mortar layers was directly related
to: l) the strength of the mortar in the layer, 2) the adhesion character
istics of the surface slab, and 3) the length of the mortar layer on the
walls close to the movable block.
The residual resistance of the mortar layer depended mainly on:
1) the strength of the mortar, 2) reinforcement of the layer, 3) the length
of the beam, and 4) the thickness of the layer.
In the ranges tested, the rate of loading had no significant ef
fect on the peak or residual resistance of the mortar layers.
3-85
CHAPTER 4
SHOTCRETE TESTS
4.1 INTRODUCTION
For the shotcrete tests the same planar geometry of the testing
device was used. However, the methods of layer application were completely
revised; the necessary equipment for placing of the shotcrete had to be se
lected, prepared and tested. The preparation of the testing device and
testing of the applied shotcrete layers followed the same procedures used
for the testing of the mortar layers. The displacements of the shotcrete
layer and of the movable block were again measured by dial gages, but the
measurement of surface strains was discontinued for the reasons given in
Section 3.5.4. The same electronic recording instruments were utilized
for measurement of the load and displacement of the rams. The subsequent
data and results are presented in a manner similar to that used for the
mortar tests.
Measurement of the displacement occurring between the fixed wall
and the surface slabs were made during two of the shotcrete tests. This
relative displacement had not been measured in the mortar tests.
The variables studied during the shotcrete tests included all of
those investigated in the mortar tests; i.e., the effects of a change in
adhesion conditions, layer strength, reinforcement and boundary conditions
were investigated. In addition to these, the effect of the thickness of
the layer was also included.
4-1
l
4.2 SHOTCRETE OPERATION
4.2.l PREPARATION OF TESTING DEVICE
Prior to shooting, the testing device was prepared to: l) facili
tate the shooting operation, 2) set up the required test conditions, 3) fa
cilitate the preparation of the shotcrete layer for testing; and 4) mini
mize the effects of other variables on test results.
Several measures were taken to facilitate the shooting operation.
The entire testing device was surrounded by plywood wingwalls which would
confine the rebound to a sll)all area. These wingwalls are shown in Fig.
4.1 Vertical guide wires were placed to assist the nozzleman in spraying
the shotcrete to the required thickness. These wires were installed at dis
tances corresponding with the desired thickness of the layer. They can
be seen in Figs. 4.1 and 4.2. Finally, the floor in front of the test wall
was covered with canvas tarps to facilitate clean-up a.fter shooting.
The required adhesion cond~tion was obtained by preparing the
concrete surface slabs before shooting. For those tests in which a good
bond between the shotcrete and the slabs was desired, the surface of the
slabs was roughened with a wire brush. The re1 3tive roughness of the sur
face was then measured and recorded by the device discussed in Appendix B.
For those tests representing low adhesion, the slab surface was covered
with nylon filament tape. The entire area of the test (2 ft x 10 ft) in-'
eluding the movable block was covered with tape. The tape was cut along
the joints between the movable block and fixed wall. The tape-covered
strip can be seen across the upper movable block in Fig. 4.3.
4-2
l
FIGURE 4.1 FRONTAL VIEW OF TESTING DEVICE WITH PLYWOOD WINGWALLS
FIGURE 4.2 CLOSE-UP SHOWING VERTICAL SCREED WIRES AND TAPED SURFACE
4-3
FIGURE 4.3 FRONTAL VIEW OF COTTON-FILLED MOVABLE BLOCK-SURROUNDING SLOTS
The surface of the movable block was made flush with that of the
fixed wall to assure a uniform thickness of shotcrete.
To reduce the difficulty in removing excess shotcrete and dis
turbance to the shotcrete layer before testing, several measures were taken
before the shotcrete was applied . Filament tape or oil was used to cover
those areas of the wall where the shotcrete was to be removed. For tests
with fiber reinforced shotcrete, t he test strips were framed with wood boards
so that excess shotcrete could be removed without chiseling. This re
duced greatly the disturbance to the layer during trimming.
For many tests, steel plates were used as boundaries of the shot
crete layer. These plates were held by rods which passed through the wall,
the surface slab, and the shotcrete layer. Drilling of holes through the
4-4
shotcrete to accommodate these rods was avoided by extending the rods out
of the surface of the wall before shooting. The rods were then covered
with tape to preserve their threads.
To provide the same testing conditions except for the parameter
being studied, great care was taken in the preparation of the test wall.
The presence of shotcrete within the joints between the movable block and
fixed wall was eliminated by placing cotton in the open slots (see Fig.
4.3). To provide a uniform surface,the same type of tape and surface pre
paration were employed to minimize the variation of surface roughness, and,
therefore, its effect on testing.
4.2.2 SHOTCRETE MIX
All tests were conducted using dry-mix shotcrete. The same mix
proportions were used in all the shootings with the exception of test Nos.
15 and 16 in which fiber was added. The basic mix design is shown in Table
4.1.
TABLE 4.1
DRY MIX PROPORTIONS WITHOUT FIBER
Per 1/2 C.Y. Percent lbs (kg)
Sand 575 (261) 40.8
Gravel 575 ( 261) 40.8 Cement 250 ( 116) 17.8 Accelerator 7.5 (3.4) 0.6
4-5
The grain size distributions of the sand and gravel making up the
shotcrete are shown in Fig. 4.4. The uniformity coefficient of the sand
was 2.19 while that of the pea gravel was 1.41. The combined gradation
curve for the sand and gravel is also included in Fig. 4.4. Type l port
land cement was used along with Sigunite dry-powder accelerator. The ac
celerator was added in a proportion of 3 percent by weight of cement.
The mix design for test Nos. 15 and 16, in which fiber was used,
is shown in Table 4.2. The percent of fiber added was approximately 3 per
cent by weight and l percent by volume. U.S.S. Fibercon steel fiber, 0.010
in. x 0.022 in. x l in. (0.0254 cm x 0.0559 cm x 2.54 cm) was used in the mix.
Sand Gravel Cement Fiber Acee l era tor
TABLE 4.2
DRY MIX PROPORTIONS WITH FIBER
Per 1/2 C.Y. lbs (kg)
575 (261) 575 (261) 250 (116) 43 (19.5) 7.5 (3.4)
Percent
39.6 39.6 17.2 3.0 0.6
Water was added to the dry-mix materials at the nozzle. A pre
liminary measurement of the amount of water injected at the nozzle indi
cated that the water-cement ratio of the shotcrete as it left the nozzle
was approximately 0.50.
4-6
-
·-
-
U.S. STANDARD SIEVE NUMBER 4 • 2• 1-1/2" 1" .114" 1/2" 1/4" 4 6 I 10 12 16 ZO JO 40 !10 10 100 140 200 270 400
,oo • 11 I i I' i ■'r"'"',.. ' i ' i i ' ' _'._Jl.11.f'.LLL I II 111 I I I I lo , 0 '- fTI I I I I I 111111 I I I 110
' 1111 1 I I I
,o "-.~ . - I I I I I I 120
- r-Sand /i I ~
7011 t I I I I I I 111 I I I I I I I 1111 I +-+-+·--+ • v I -- t-
' IJ J: ~ 1: 1 r t , ; 1 ,, l'1 - ~- u ----· ·--~- ---~--- !:? Cl 60 ·-- -- 40 w ii:j I I ! ' : • - - ._ ----~-- - - ·---·· -- ·-·--· H- -~ -- --~------ ~-~- - --·- -- ~ ► . \.. , I I
; E ·-· -- :--::_~ rt-==- ! r--~ -- -J - - +t- - - - --~~- - EI f •o - . .!.: ___ ~) t' ~ · ' 1 +--~ _.__, Combined - .... • ·· -- --- eo u
. I I : I I . 'I I ---- '\ V I ... t . . l ·+1 • . ~ ..... \,I + II I ...
~ - rt H:_ -. i~-~--1 i i·'-'-Gra~el_/ •-~-._ ··-:-:=_ ~~ ~ \ ·-=- ·---- tf""" _ ....... ~'""t·.. ~=-=-= 1C; ~ ~~ ~~-i --~ I ---- hi}~ --± -- l"I .. , 1 -- - ·-· I i . ~ -~ . - '·-r- ,•· -- --- D..
10ftf ~= ~ = =-= tt~=~ ~- ___ ___ _ \ . I I __ -_ _ j-~- ----- eo ·: i , ,\ I
10-tt- · I - ~ ;j I I r'-. ~
I I I I i-+++--+-+-· ---190
;· ~ - 1 Ii 1 11 -;-i:..._ -- 1 I 11'.. JI Iii I ,I I , I I 111 I I I I I I I
0 -1000 SO() 100 50 10 5 ,0 1.0 0 .5 0 ,I 0 .05 0.01 0 .00, 0 .00f GRAIN SIZE IN MILLIMETERS
LW'IED COBBLES SILT or CLAY
MIT CLAY
Toroedo sand: eea gr:alle] :
Natural water content: 10. 0% N;:it11r;:i l w;:i h::>r r nntont • l 7 °L % Passinq #200 sieve: 1.0% % Laraer than 3/8 11 (ln mm) l O'¼ D60/D10 = 2.19 060/D10 = 1.41 · -
-· ·-------
FIG. 4. 4 GRADATION CURVES.
4.2.3 EQUIPMENT
The equipment used to place shotcrete consisted of a mixer, a
belt conveyor, and a dry-mix shotcrete machine. The mixer was an electric,
rotating drum type mixer having a 1/2 C.Y. (0.382 m3) capacity. The ma
terial, after leaving the mixer, was conveyed to the gun by a gasoline
powered, belt conveyor. The gun, a Reed Model LASC II, was used to spray
the shotcrete onto the surface of the model. The material was conveyed
to the nozzle in a 2 in. (5.08 cm) diameter hose having a length of 100
ft (30.4 m). A stepped-balloon nozzle having a length of 1 ft was used
to direct the material onto the wall. The water was delivered by an
ordinary garden hose and regulated by a screw valve at the nozzle. The
water ring had an inside diameter of 2-1/2 in. (6.35 cm) and contained
four holes 3/16 in. (0.476 cm) in diameter, symmetrically placed around
it. A photograph of the nozzle can be seen in Fig. 4.5. The arrange
ment of the equipment is shown schematically in Fig. 4.6, and pictured in
Figs. 4.7 and 4.8. In both Figs. 4.7 and 4.8, the shotcrete machine is
shown at the extreme left.
In the first several tests, the accelerator was added at the
gun using a screw-feed accelerator dispensor. However, difficulty in the
operation of this device made it necessary to manually add the accelerator
to the material as it passed on the conveyor.
4.2.4 SHOOTING PROCESS
Since the mixer had only a 1/2 C.Y. (0.382 m3) capacity, the
4-8
FIGURE 4.5 NOZZLE CLOSE-UP
4-9
~ I __,
0
Sand Gravel Cement (Fiber)
aterial
\. Mixer -'
-
Acee 1 era tor Air-pressure Water
Sho.tcrete - Conveyor Gun Hose Nozzle --
FIGURE 4.6 SCHEMATIC ARRANGEMENT OF THE SHOTCRETE EQUIPMENT
FIGURE 4.7 ARRANGEMENT OF SHOOTING EQUIPMENT
FIGURE 4.8 CLOSE-UP VIEW OF BELT CONVEYOR AND POWERED GUN
4-11
shotcrete had to be prepa red in several batches. To provide a nearly
continuous shooting operation, the material for each batch was pre-weighed
and stored in drums. Thi s assured a minimum batching time dur ing gunning
of the model.
For each batch the required amounts of sand, gravel, cement, and,
for test Nos. S-15 and S-16, fi ber were loaded into the skip and then dumped
simultaneously into the mi xer. When fiber was added, a sieve with 1 in.
(2.54 cm) square opening wa s used, as shown in Fig. 4.9, to break up any
entangled balls of fi ber . The batched materials were always mi xed a
minimum of 3 minutes. The ra t e of material transported to the gu n was con
trolled by the speed of the con veyor and was set so that the time of the
material in the hopper remained ess entially the same. The accelerator was
manually added onto the conveyor.
The first batch was gunned against a plywood practi ce wall, as
shown in Fig. 4.10, which was located away from the testing device . This
allowed the nozzleman and gunman to adjust the air pressure and r otation
speed of the machine so that a smooth, continuous flow of ma ter ial would
be delivered to the nozzle whi le shooting the surface of the model. During
th i s time a 2 ft x 2 ft x 3 i n. (61 .0 cm x 61 .0 cm x 7.62 cm) test panel
was also gunned to obtain sampl es fo r strength tests. An empty test panel
is shown in Fig. 4.10, the shooting of the test panel is shown in Fig. 4.11,
and a filled panel is shown in Fig . 4 .12.
After the complet i on of the practice shooting, the shooting oper
ation was then moved to the test wall. The wall was first cl eaned using an
air-water jet from t he no zz l e. This removed any dust accumul ated on the
4-12
FIGURE 4.9 FIBER SCREENING USING 1-IN. (2.54 CM) SIZE SIEVE
FIGURE 4.10 WARM-UP SHOOTING AGAINST PLYWOOD WALL
4-13
FIGURE 4. 11 STRENGTH-SPE CIMENS PANEL BEING FILLED UP
FIGURE 4. 12 FINISH ED STRENGTH-SPECIMENS PANEL
4-14
surface of the slabs and prepared them for receiving shotcrete. The first
material delivered to the nozzle was shot against one of the wingwalls so
that the air pressure and water could be adjusted without placing poor
quality shotcrete. After these adjustments were made, the stream of ma
terial was directed against the test wall surface. The shooting began in
the lower right corner of the test wall and followed the path shown in
Fig. 4.13. The nozzleman used the guide wires to obtain a uniform thick
ness. For all shootings,the shotcrete was placed in a single layer. How
ever, additional materials were placed over indentations in the first
layer to obtain a relatively uniform thickness. The time between the
shooting of the first layer and patching of thin areas never exceeded 30
minutes.
FIGURE 4.13 PATTERN OF SHOOTING
4-15
During shooting, the air pressure at the gun ranged from 60 to
75 psi (4.22 to 5.27 kg/cm2). These pressures produced a material delivery
rate (including water) of 400 ·to 450 lbs/min (181 to 204 kg/min). The same
air pressure was used for all shootings in order to obtain approximately
the same compaction and thus the same strength in all of the tests. The
rate of water flow to the nozzle during one shooting was approximately 24.0
to 27.0 gal/min (1.51 to 1.70 l /min).
After the entire wall was covered with a layer of shotcrete, a
second test panel was gunned. This panel, like the first, was used to ob
tain samples for strength tests which were performed simultaneously with
the large scale test. In addition, for test Nos. S-13 to S-16, another test
panel was shot to obtain samples for adhesion tests. For test Nos. S-13 and
S-14, a 1-ft x 1-ft x 3-in. (30.5 cm x 30.5 cm x 7.62 cm) concrete slab was
used for the adhesion test panel. To reduce the difficulty of cutting the
adhesion test samples, a concrete slab was pre-cut to the desired sample
size. A 4 x 6 array of 2 in. x 2 in. x 3 in. deep (5.08 cm x 5.08 cm x
7.62 cm) concrete blocks, joined together by brittle plaster, was used for
test Nos. S-15 and S-16. The shotcrete-slab adhesion samples were procured
by cutting only the shotcrete l ayer. This procedure permitted samples to be
obtained for early adhesion tests.
4.2.5 CURING
Immediately after the shooting, the plywood wingwalls were removed
and the shotcrete layer was trimmed around the top and bottom of each mov
able block and fixed wall slabs. For all tests, except those containing
4-16
steel fibers, the trimming was accomplished by chiseling along the bound
aries of the test layer. The removal of the surrounding material was facil
itated by placing the tape or oil on those areas to be trimmed. For the
steel fiber shotcrete tests, boards were placed horizontally along the ex
treme upper and lower boundaries of the layers. These boards were easily
removed and an evenly trimmed edge was obtained. Only the 3-in. (7.62-cm)
wide strip between the two test layers had to be removed using a hammer
and chisel. The guide wires were left embedded in the shotcrete to avoid
disturbance to the test layer. Figure 4.14 shows a non-fiber reinforced
shotcrete layer after it was trimmed.
After trimming, burlap was placed over the shotcrete layer and ,
moistened. The burlap was then covered with plastic sheets to retain the
moisture. Periodically the burlap was rewetted to provide a constant moist
curing environment for the shotcrete. A photo of burlap and plastic placed
over test layers can be seen in Fig. 4.15.
The 2-ft x 2-ft x 3-in. (61.0 cm x 61.0 cm x 7.62 cm) shotcrete
panels were placed in a concrete curing room in which humidity and tem
perature conditions were similar to those surrounding the shotcrete in the
model. Panels were kept in the room until it was time for preparation and
testing.
The adhesion test panels were covered and cured in the same manner
as shotcrete on the test wall; they were covered with burlap and plastic, and
periodically moistened. This was done so that the adhesion of the test speci
mens would match as closely as possible that existing on the test wall.
These panels were also cured unt i l just before testing.
4-17
FIGURE 4.14 FRONTAL VIEW OF SHOTCRETE LAYERS IMMEDIATELY AFTER TRIMMING
FIGURE 4.15 FRONTAL VIEW OF SHOTCRETE LAYERS DURING CURING PROCESS
4-18
4.3 SHOTCRETE TEST PROGRAM
The shotcrete test program was set up using the same hypotheti
cal model of thin layer behavior shown in Fig. 3.5. Based on the results
of the mortar tests, modes of failure were predicted for the shotcrete
layers. The same variables, but including reinforcement, were reassessed
in terms of the structural behavior of shotcrete rather than mortar.
All shotcrete layers covered the full width of the model. This
application assured that adhesive stress would be fully mobilized along
the portion of the fixed walls bordering the movable block. In addition,
full coverage of the surface of the model permitted a wide range in the
spacing between the steel plates which formed the lateral boundaries of
the layer. For all tests a loading rate of 5 lbs/sec (22.2 N/sec) was
used in applying the load from the ram to the movable blocks.
The parameters selected for study in the shotcrete tests in
cluded: 1) lateral boundaries of the layer, 2) adhesive strength, 3)
shotcrete strength, 4) thickness of the shotcrete layer, and 5) rein
forcement. The manner in which these parameters were varied and the
values assigned to them in the 16 shotcrete tests are summarized in
Table 4.3 and described in the following sections.
4.3.1 LATERAL BOUNDARY CONDITIONS OF THE LAYER
In most tests the lateral boundaries of the shotcrete layers were
established by steel plates simulating rock bolts or boundaries of openings
in actual tunnels. Steel plates were not used in five of the shotcrete
tests (test Nos. S-1, S-2, S-3, S-5 and S-7 - Table 4.3) This case
4-19
TABLE 4.3
MATERIAL PROPERTIES OF SHOTCRETE LAYERS
COLUMNS 1 2 3 4 5 6 7 8
Comp. Flexural E Rock bolt Test Thickness Adhesion strength strength
106psi/GPa Length at
no. in./mm psi/kPa psi/MPa psi/MPa in./m ft/m
S-1 1.82 180 3580 565 3.64 48 None 46.23 1241 24.7 3.9 25.10 1.22
S-2 1.70 180 3580 565 3.64 48 None . 43.18 1241 24.7 3.9 25.10 1.22
S-3 2.18 187 4890 3.08 48 None 55.37 1289 33.7 21.2 1.22
S-4 2. 11 20 4890 3.08 48 8 53.59 138 33.7 21.2 1.22 2.44
S-5 5.26 185 3830 740 4.70 48 None 133. 60 1276 26.4 · 5. l 32.4 1.22
S-6 4.70 20 3830 740 4.70 48 8 119.38 138 26.4 5. 1 32.4 1.22 2.44
S-7 2.78 60 910 250 2.30 48 None 70.61 470 6.3 1.7 15.9 1.22 2.44
S-8 2.95 10 910 250 2.30 48 8 74.93 69 6.3 1.7 15. 9 1.22 2.44
S-9 2.65 154 2400 450 3.70 48 4 67.31 1062 16.5 3. 1 25.5 1.22 1.22
S-10 3.07 37 2400 450 3.70 48 4 77.98 255 16.5 3. 1 25.5 1.22 1.22
S-11 5.24 45 718 80 0.86 48 8 133. 10 310 5.0 0.3 5.9 1.22 2.44
S:-12 5.46 20 718 80 0.86 48 8 138.68 138 5.0 0.3 5.9 1.22 2.44
S-13 1.80 185 2850 141 7.34 48 8 45. 72 1276 19.7 1.0 50.6 1.22 2.44
S-14 1.06 187 2850 141 7.34 48 8 nr "" 1;:o::, I~•/ Lu 50.6 1.22 2.44 c..v. "3C.
S-15 3.66 3450 930 48 8 92.96 23.8 6.4 1.22 2.44
S-16 4.43 3450 · 930 48 8 112. 52 23.8 6.4 1.22 2.44
4-20
would represent a tunnel in which bolts were not installed or were placed
only locally. In nine of the tests, Nos. S-4, S-6, S-8 and S-11 to S-16,
the steel plates were located at 8 ft (243.2 cm) apart. Finally, for two
of the shotcrete layers tested, Nos. 9 and 10, the distance between the
steel plates was equal to 4 ft (121.6 cm) or l ft (30.4 cm) from the edge
of the movable block.
These steel plates were used to provide a restriction to propa
gation of an adhesion failure and to evaluate the residual resistance of
the layer acting as a beam. Variation in the spacing of the steel plates
was not expected to have an effect on mode of failure or the maximum
res istance of the shotcrete layer.
4.3.2 SH0TCRETE STRENGTH
The variation in shotcrete strength was obtained by testing the
layers at different times after application of the shotcrete.
The strength of the shotcrete in the layer was estimated by per
forming standard compression and flexural tests on shotcrete specimens ob
tained from the sample panels. These tests were conducted at approximately
the same time as the model tests and were used for strength control. In
some of the model tests, strength tests were also carried out on shotcrete
samples cut from the failed shotcrete layer. A comparison of the strength
results from the two sets of samples indicates that the shotcrete in the
panel is representative of the shotcrete placed on the surface of the
model. Columns 4, 5 and 6 of Table 4.3 show the compressive and flexural
strengths and the initial tangent modulus of the shotcr ete in the test panels.
4-21
The average values of adhesive strength for shotcrete cured 7 days varied
from 180 psi (1241 KPa) for roughened surface slabs to 20 psi (138 KPa)
for the surface slabs covered with filament tape. When the shotcrete was
cured for 7 hours, the average values of adhesive strength ranged between
77 psi (531 KPa) and 10 psi (69 KPa).
The variation in adhesive strength with time of curing repre
sented by the unconfined compressive strength and surface conditions is
shown in Fig. 4.18. In this figure the average values of the adhesive
strength for both the roughened and taped surfaces are plotted against
the compressive strength of the shotcrete. The greatest difference in
adhesive strength occurred between samples having roughened concrete and
taped surfaces at 7 days and between samples having rough surfaces but
tested at 7 days and 7 hours. The test results further show that adhesive
strength is insensitive to time of curing for poor bonding conditions.
The adhesive strength of the shotcrete on the roughened concrete surfaces
was approximately twice that on the taped surfaces at 7 hours.
The tensile load vs deformation data obtained from the adhesive
tests indicate that the stiffness .in adhesion is very high and that the
mode of failure is very brittle (Fig. 3 - Appendix C). Almost no dis
placement occurred at the contact during the loading process before failure,
and after failure had occurred the resistance immediately dropped to zero.
Finally, the adhesion failure did not always occur along the
shotGrete-concrete contact but sometimes took place along laminations in
the shotcrete. The adhesive strength values obtained in these cases were
not used in computing the average adhesive strength of the layer.
4-22
The compressive strength of the shotcrete varied from a maximum
of 4890 psi (33.7 MPa), in test Nos. S-3 and S-4, to 718 psi (5.0 MPa) in test
Nos. 11 and 12. Variations in the strength of shotcrete having approxi
mately the same curing time are related to variations in the shooting pro
cess and in its ingredients.
4.3.3 ADHESIVE STRENGTH
The adhesive strength between the shotcrete and concrete surface
slabs covering the walls was varied directly by changing the adhesive char
acteristics of the surface slabs, and indirectly by varying the shotcrete
strength.
Column 3 in Table 4.3 shows the average values of the adhesive
strength between the shotcrete layers and the surface slabs obtained from
the tests on the 2-in. x 2-in. x 6-in. (5.08-cm x 5.08-cm x 15.2-cm) sam
ples cut from sections of the test layer. In most of the cases, the sam
ples were taken from either the slab on the movable block or from locations
close to the edge of the fixed walls where little or no disturbance of the
layer took place during testing. Figure 4.16 shows a typical facing slab
covered with shotcrete from which the adhesion test specimens were cut.
The samples were prepared so that the interface between the shotcrete and
concrete slab was located in the middle of the prism.
The test apparatus used, the procedure followed, and all of the
results obtained in the adhesion testing program are described and sum
marized in Appendix C.
4-23
FIGURE 4.16 COMBINED SHOTCRETE-SLAB SECTION AND CORRESPONDENT ADHESIVE TEST SAMPLES
FIGURE 4.17 ADHESIVE TEST SAMPLES AFTER TESTING
4-24
0 0
0 0
Adhesive strength, kPa 0
0 0 0 0 0 0
0 0 0 0 0 0 N c;:t- I.O
0 N ..t- I.O co ~
I 8-----...------,-------,-------,--------, 0 co
0 0 0 r---
0 0 0 I.O
0 0 0
. ,... LO 1/)
Cl.
..r::::. +> CJ')
C Q.) 0 s.. 0 +> 0 1/) c;:t-
Q.)
> ...... Vl Vl Q.)
s.. Cl. E o O 0
U 0 M
0 0 0 N
,,,,,,.-....... ( .4 '\ \ \ \ \ I I I I
I I I I I I I I
1, 10• I __ / 7 hours taped surface
7 days taped surface
--........ / ( .3 \ \ \ \ I I I I I 1 •s I
/ •1•2 / I I
I I I I
/ 13" / / 14;
I I l •9 / , __ ..,,/
7 days roughene surface
g _/ ---, /As \ /- 7 ■ ' 7 hours
roughened surface
\ •12 \ t• 11 .,) , __ ; ...... __ _ Oo!,------,.,..-----,.,..-----,.,..-----:0"":--------;,!o
0 LO 0 LO N N
Adhesive strength, psi
FIGURE 4.18 ADHESIVE STRENGTH VS COMPRESSIVE STRENGTH OF THE SHOTCRETE LAYERS
4-25
0 0 co
LO LO
0 LO
LO M
~
..r::::. 0 +> M C'>
C Q.)
s.. +> Vl
LO QJ N > ......
Vl Vl Q.)
s.. Cl. E
0 0 NU
Lt')
0
LO
0
4.3.4 THICKNESS OF THE LAYER
Column 2 in Table 4.3 shows the average thicknesses of the shot
crete layers. These thicknesses are typical of those used in practice for
thin linings, and ranged from a maximum of 5.46 in. (13.9 cm) in test No.
S-12 to a minimum of l .06 in. (2.69 cm) in test No. S-14. These values
represent the average thickness measured along the failure cracks in the
layer. The measurements show a remarkable uniformity in the thickness of
all the layers shot (±0.l in.) (0.254 cm).
4.3.5 USE OF REINFORCEMENT
Two of the tests, Nos. S-15 and S-16, were conducted on shotcrete
containing steel fibers, 1-in. x 0.010 in. x 0.022 in. (2.54-cm x 0.254 mm x
0.559 mm). In each test 144 lbs (65.3 kgms) of steel fiber corresponding to
3 percent by weight or percent by volume of the entire batch were added to
the mix.
The presence of steel fibers added to the materials in the above
proportions has been shown to increase the tensile strength of the shotcrete
(Parker, et al., 1975) or at least improve its ductility. It was therefore
expected that reinforcing with the steel fiber would affect the residual re
sistance of the shotcrete layer without changing its mode of failure or maxi
mum resistance.
4.4 TEST RESULTS
The shotcrete layer test results were plotted and analyzed in the
same manner as those obtained in mortar tests. The load in the jack repre-
4-26
senting the resistance of the shotcrete layer was plotted against the 11 net 11
displacement of the movable block. The relative forward displacement of the
shotcrete layer was obtained for each load increment by subtracting the dis
placement of the 11 fixed 11 walls of the test device with respect to the floor.
The displacement of the wall was quite small (0.001 in.; 0.025 mm) compared
with the displacement of the movable block.
4.4. l MODES OF FAILURE
The two basic modes of failure shown in the conceptual model in
Section 3.3 were observed in the shotcrete layers. Column 2 of Table 4.4
shows the mode of failure for each shotcrete test.
A diagonal tension failure occurred in tests S-1, S-2, S-13 and S-14.
(Fig. 4.19).
FIGURE 4.19 FRONTAL VIEW OF FAILED SURFACES IN TEST NOS. l AND 2
4-27
TABLE 4.4
SHOTCRETE LAYER TEST RESULTS
COLUMNS 1 2 3 4 5 6 7 8 9 10 11
Length Length of of
Max. t,_ Residua 1 t,_ develop develop I EI Curing Test Failure load failure 1 oad residua l ( 1 eft) (right)
. 4; 4 106. 4; 4 time
no. mode 1 bf / kN in./mm l bf /kN in./mm in./m in./m 1n . cm ,n. m hrs
S-1 Shear 15,250 0.01 0 0.10 9 30 12.06 43.9 72 67 .8 0.25 0 2.54 0.2 0.8 502.0 18.3
S-2 Adhesion 13 ,250 0.01 0 0.15 5 3 9.83 35.8 72 -Shear 58.9 0.25 0 3.81 0. l 0.08 409.2 14.9
S-3 Adhesion 17.375 0.02 2800 0.06 48 15-1/2 20.72 63.8 144 77 .3 0.51 12.5 1.52 1.2 0.4 862.4 25.6
S-4 Adhesion 2,500 0. 01 2600 0.04 36 36 18.79 57.9 144 -Bending 11. 1 0.25 11.6 1.02 0.9 0.9 782. l 24.1
S-5 Adhesion 17,500 0.04 0 0.04 48 48 . 291.06 1368.0 168 77 .8 1.02 0 1.02 1. 2 1.2 12114 .8 569 .4
S-6 Ad hes ion 4,550 0.03 3200 0. 12 36 3b 207.65 975.9 168 -Bending 20.2 0.76 14.2 3.05 0.9 0.9 8643.0 406.2
S-7 Adhesion 5.500 0.02 5200 0.27 24 48 42.97 98.8 7 24 . 5 0 .51 23. 1 6.89 0.6 1.2 . 1788. 5 41. l
S-8 Adhesion 1,700 0. 01 500 0.15 36 36 51.34 118. 1 7 -Bending 7.6 0. 25 2.2 3.81 0.9 0.9 2136.9 49.2
S-9 Adhesion 20,250 0.03 0 0.50 12 12 37.22 137. 7 144 -Bending 90. 1 0.76 0 12 .70 0.3 0.3 1549.2 57.3
S-10 Adhesion 7,000 0.06 6960 0.30 12 12 57.87 214.l 168 -Bending 31. 1 1.52 31.0 7.62 0.3 0.3 2408.7 89.l
S-11 Adhesion 6,620 0.02 2970 0.05 36 36 287.76 247.5 7 29.4 0. 51 13.2 1.27 0.9 0.9 11977 .4 103.0
S-12 Adhesion 2,640 0.02 1300 0. 10 36 36 325.54 280.0 7 11 .7 0. 51 57.8 2.54 0.6 0.6 13550.0 116 .5
S-13 Shear 19,930 0.07 0 0.08 9 12 11.66 85.6 192 88.7 1.78 0 2.03 0.2 0.3 485.3 35.6
S-14 Shear 7,250 0. 01 350 0.04 7 7 2.38 17.5 192 32.2 0.25 1.6 1.02 0.2 0.2 99. l 7. 3
S-i5 Auite!; i Uri 14 ,.JI:> u. 10 38<+0 0.36 8 3 i68 -Bending 63.9 4. 06 17 . 1 9. 14 0.2 0.08
S-16 Adhesion 4 ,100 0.08 1440 0.45 48 48 168 -: Bend i ng 18 .2 2.03 6.4 11 .43 1.2 1.2
4-28
The type l curve is characteristic of diagonal tensile failures
in which an immediate and complete reduction of layer resistance was ob
served after failure (test Nos. S-1, S-2, S-13 and S-14). A similar be
havior is shown by the type 2 curve, typical of test Nos. S-3, S-5 and S-7,
in which no steel plates were used and the adhesive failure propagated at
least on one side to the margins of the layer. Once the maximum resistance
of the layer was reached, however, it was held temporarily during additional
displacement (up to 0.05 in.) of the movable block.
The type 3 and 3A curves reflect the structural behavior of the
remaining layers. In these layers an adhesive failure initially developed
between the shotcrete and the surface slab. However, the steel plates on
the fixed block limited the lateral extent of this adhesion failure and
allowed t ;,e layer to behave as a beam.
The character of the residual resistance shown by the 3 and 3A
curves depends on the ductility and flexural strength of the shotcrete
layer as well as the spacing between the steel plates. The type 3A curve
is typical of the results obtained from tests in which shotcrete was placed
against filament tape (low bond strength). The presence of the tape re
duced the adhesive strength, therefore decreasing the maximum resistance of
the layer. In this case the adhesive strength was nearly the same as the
bending capacity of the layer. Type 3 curves were obtained when shotcrete
was in contact with roughened concrete.
The resistance-displacement relationships for all the shotcrete
tests are shown in Figs. 4.21 to 4.28. The maximum resistance and block
4-29
(/)
I-z: LLJ ::::E: LLJ u ex:: ...J 0.. (/) ..... Cl
~ u 0 ...J
V') c::i +-> LLJ c:: Q) ...J E c::i Q) ex:: u > rt! 0 ,- ::::E: c..
(/) V') ..... > -c:,
LLJ ~ u u :z: 0 ex::
I ,- I-..0 l '1
I .....
Q) (/)
I ,- LLJ ..0 ~
/ ~ :::c > / 0 I-
::::E: <.!J z: LLJ ...J
I-..... z: :::,
0 N
G .
<::I'"
LLJ ~ :::, <.!J ..... LL
0
4-30
-Movable block displacements (rm1)
0 0.25 0.50 o. 75 l I OQ 1. 25 1.50 1. 75 2.00 I I I I I I I I I -,90
500 I I I I -·• 80 __
C: ' .... E ......... ......... 4- z: .&:I ~ ,- -- 400 70
Shotcrete +' +J u V 11' _.,,
~Scale I +' +J C:
C 0 ·o 2'0 in·. 60
u ·v 4-.... 0
()
300 ..c .c +' +J
50 Ol ' t:n C:
i Q) ,--+J +' .... ·- 40 C:
C :::, ~ - ::,: I , s...
w L Q) __, a, 0. ~
30 Q)
a, u u C: C 11' It! +' +J 1/) VI •,-....
20 1/)
VI Q)
~ 100 c:::
10
0 .__ _ _._......., ____ ......_ ___ __. ________ ---' ____ ...._ _________ __.
0 10 20 30 40 50 60 70 80 0
Movable block displacements (10- 3 in.)
FIGURE 4.21 UNIT LENGTH RESISTANCE VS KJVABL£ BLOCK DISPLACEMENTS
Movable block displacements (nm) 0 0.25 0.50 0.75 1·, 00 JI 25 J,ro l. 75 2.00 I I I I I I I 90 -,
500
I I I I I I •
£, 1~4 i~-~tc!i Jack I
,}(4 ;~~ I 80
I .q««tp«««<<«««<«y I ''""''"""""'1P"'"l fot' I I -. C:
'112' ¥73WIWTiiW ilCi 'f tf:4 1•·•,::-li llt:31• ·· '@I ~ ·- 70 E ......... 400 ......... .....
0 Shotcrete z .J:I ~ _. - ...._;,
1~ca le., .µ .µ u u 20 in. 60 tO l'CS .µ .µ
C: C: 0 0 u u 300 ..... .....
0 50 0
.c: .c:
.µ .µ O'l O'l C: C: Q) Q)
40 _. _. ~ .µ I .µ
200 •r-w .,... C: N C: ::, ::,
s.. 30 s.. Q) Q) 0.. .. 0..
Q) Q) rS-4 u u 0 C: C:
tO ,a 100 .µ .µ
V) V) .,... .,... V) V) Q) Q)
10 c::: c:::
00 10 20 30 40 50 60 70 80
Movable block displacement (10- 3 in.) FIGURE 4.22 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
-
- Movable block displacements (mm) 0 0.5 ],Q 1.5 2.Q ,-~ 3,Q 3,5 410
' I I I I I I -,90 500
I 1/4 11
Jack /St.pl. for I -----130
........ t J;.,, ,,,,,., .. J,. .t;J't~~:±~ S-6 ........ . E C '-.....
70 . ~ :;:- 400 S-5 ...,_... ..c ,--......,. +)
,~cal~ u tO +) +) - u 20 in. 60 C: ro 0 +) u C
0 . It--u 300 0 4-
50 .c 0 +) 0, .c C +) QJ Ol
C ,....
QJ
0 +) .i:::, ,-- .,... I
C: w +) 200 ::, w ..... C s.. ::,
QJ
30 0. s... QJ
Q) 0. u S-6 C QJ tO u +) - C 20 Ill ro ..... +) 100 Ill Ill QJ .....
0::: Ill QJ
0::: -- l.J -110 ---- --------.- -~ - -- ....
0 160 - 0 0 60 80 l 00 120 140
Movabl e block disp lacemen t s (10-3 in.)
FIGURE 4.23 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS .._.
.-
Movable block displacements (nm)
0 2.5 5. 0 7.5 10 .0 12.5 15.0 17. 5 20.0 I
90 -500 I I I I I
1!1~ i~~ I I I I 1/4 in. St~ £, ~-·- r n ack
80 . - q::::r+,iL.[~] ~~~ . -C: E .,...
....... ....... il 400 70 z
~ ,- o Shotcrete -: - - +J +J
1~ca 1 e--1 u
u ,a n, ' 20 in. 60 +J +J C: C: 0 0 u u . '+-
'+- 300 0 0 50 .&::.
.&::. +J +J en en C: C: cu cu ,-,-
40 +J ~ I +J .,-
w .... ,- C: ~ § 200 :::,
s.. s.. cu cu 30 c.. c.. S-7 cu .... cu u u C: C: ,a
+J n, 20 VI +J
-~ 100 .... VI cu Vl S-8 0:: cu
0::
10
0 100 200 300 400 500 600 700 800
Movable block displacements (10- 3 in.)
- FIGURE 4.24 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
- Movable block displacement (mm)
0 2.5 5.0 7.5 10.0 12.5 15 .0 17.5 20.0 I I I I I I I I I 790 500, I I I I 1 1/4" Steel~ I 1 /4" I r nl :.+o .l::ir-L- /<:.+ ... ,
80 I //VU.,,<««<<<""""'f ~ .
I r'"''««««<O:?'"~ I I -. C: .,... • ......... --r- to- ~ShotcrTte 70 E 4--
.CJ ......... z ,.... ........ ~
1~cal ~I ..__..
~ u .µ - "'
20 in. 60 u ~ "' C:
.µ
0 . i:::
u 0 u
S-9 4-- 4--0 50 0
.s= ~
..i:::
O') .µ
C C"l
QJ
' i:::
.J:::, ,.... 40 QJ
' ,....
I ~ w .,... 200
' .µ
c.n §
.... ' i::: ....... :::,
s... .._ ..._ 30 8.
s...
--- QJ c..
QJ u QJ
C u - ,a 20 i:::
~ "' "'
.µ Vl .....
"' .,...
QJ Ill
~ QJ
10 ~
0 -1'
0 100 200 300 400 500 0
600 700 800 Movable block displacements (lo-3 in.)
FIGURE 4. 25 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
-
--
-
--
-
Movable block displacements (rm,)
0 0.5 l.O 1.5 2.0 2.5 3.0 3.5 4.0
soo-------------------------.,....--------------
..i::,. ·
---C
•,-......... ~ 400 ,-. -.µ u ltl .µ C 0 u
'+- 300 0
..c .µ O'> C QJ
,-.
I .µ w •,-0) • § 200
s... QJ C.
QJ u C: ltl .µ VI . ,-VI QJ
er:::
20
0
S-11
40 60 80 100 120
Movable block displacements (10- 3 in.)
FIGURE 4.26 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
Shotcrete
,Ecal~I 20 in .
140 160
90
80
70
60
50
40
30
20
10
0
---E
----z ~
.µ u <ti .µ C: 0 u 4-0
..c .µ 0, C Q)
,-.
.µ •r-e ::::,
s... Q) C.
Q) u C <ti .µ Vl .,... Vl Q)
er:::
Movable block displacements (mm)
0 0.5 l.O 1.5 2.0 2.5 3.0 3.5 4.0 ::,...
90 500
I I I ; 1/4 in. I r!~4-~nt I I I
~ Jack C' ♦ - ,
80 ..-.... q::::r .. t .. r;:o ,..... .
E C: ........ •r-
70 z - 400 ~ 4- ...._., .D o Shotcrete ,-
+-' .__..
1~ca l e ..
1 u ,0 +-'
+-' u 20 in. 60 C tO 0 +-' u C:
0 4-u 300 0 4-
50 ..r:: ...... 0 +-' Ol .c C .µ Q) Ol
C: ,-
+'> Q) 40 +-' ,-
•r-I C w +-' ::, --.J •r- 200 S-13 - C: ~ ::, Q)
30 0.. s... <l)
Q) 0. u C Q) l,:J u +-' C: 20 VI It!
~S-14 ..... .µ 100 VI VI Q) •r-
0::: VI <l)
0::: ■ _I " . ., 0
0 - -20 40 60 80 100 120 140 160
Movab le block displacements (l0-3 in.)
-· FIGURE 4.27 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
...
...
.... 0 2.5
I I 500
-. s:::
•r-....... 4-..c 400 .-
+.> u co
+-' s::: 0 u - 4-0
.i:,,. .s::. I +-'
w O'l co s:::
Q) .....
-- +-' •r-s::: ::::,
s.. Q) a. Q) u C: co
+-' Vl
•r-Vl Q)
0::: I I ~
5.0
I
Movable block displatemen~s (11111)
7.5 10.0 12.5
I I I
-·--
S-15
S-16
"'" -' - ---
500
Movable block displacements (10-3 in.)
15.0
I
I . I o -·
-~--
FIGURE 4.28 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
17.5 20.0
I I 90
80 -E ....... z ~
70 -+.> u C0
+.> C:
60 0
iScal H u 4-~o in. 0
.s::. 50 +.>
O'l C: Q) .....
+.> 40 •r-
C: :::,
s-Q) c..
30 Q) u C: ,,;
+.> Ill
20 •r-Ill Q)
ar::
I I
10
0
displacement obtained in each test are summarized in Table 4.4. Column 5
of the same table shows the value of the residual resistance after the ad
hesive failure reached its lateral boundary.
From the values given in Table 4.4, and the curves shown in Figs.
4.21 to 4.28, the following preliminary conclusions regarding the structural
behavior of the shotcrete layers can be drawn.
1. The movable block displacement at which the maximum
resistance of the shotcrete layers was developed varied
between 0.01 to 0.16 in. (0.25 to 4.06 mm).
2. When failure occurred by separation of the shotcrete
layer from the surface slab and no steel plates were
present, the resistance remained at the maximum value as
the separation gradually progressed outward. In these
cases the movable block reached maximum displacements
ranging between 0.04 in. (test No.S-5) and 0.3 in. (test
No. S-3)(0.10 cm and 0.76 cm) without collapse of the
shotcrete layer. This additional displacement of the
movable block indicates certain ductility in the be
havior of a thin shotcrete layer. This 11 ductility 11
depends on the adhesive strength along the total area
of contact between the shotcrete layer and the surface
slab and, more importantly, on the stiffness of the
shotcrete layer.
3. Residual resistances ranging from 30 to 100 percent of
the maximum layer resistance were observed depending on
4-39
•
the position of the boundaries, the shotcrete-slab
bond and on the flexural strength of the layer. In
these tests, the residual resistance was closest to
the maximum resistance in layers having low bond
strength and maximum thickness.
4. The presence of steel plates, simulating rock bolts
or other tunnel boundaries ,did not always have an
influence on the structural behavior of the layers.
In the cases where diagonal tension failures occurred,
the failure surface did not extend more than 12 in.
(30.5 cm) beyond the movable block, (curve type 1,
test Nos. S-1, S-2, S-13 and S-14). Only steel plates
located within 12 in. (30.5 cm) of the movable block
would have had any effect on the structural behavior
of the layer.
In addition, steel plates located more than 30 in.
(76.2 cm) from the movable block would not have had
any influence in the residual resistance of the layer
in test No. S-3. The minimum distance at which the
lateral restraints begin to influence the residual
resistance and displacement of the shotcrete layer
depends on the nature of the adhesive strength in the
vicinity of the movable block, the stiffness of the
shotcrete layer, and, of course, any weak zones in the
shotcrete layer created during or after shooting.
4-40
'
4.4.2 SHOTCRETE LAYER DISPLACEMENTS
Dial gages were placed against the front surface of the shotcrete
layer and attached to a frame bolted to the floor to measure the relative
forward displacements of the layer with respect to the floor. The displace
ments measured by these gages are shown in Figs. 4.29 to 4.43. These dis
placements were plotted in the same manner as those obtained in mortar tests.
The upper portion of the figure shows a top view of the fixed walls and
movable block, the shotcrete layer and the posit i ons of the dial gages on
the surface of the shotcrete. The displacements recorded by the dial gages
at each load increment are plotted in displacement profiles. The resistance
of the shotcrete layer at each increment is shown at the right side of the
displacement profile.
The displacement profiles before initial failure are very similar
for all tests in which adhesion failure occurred. Initially, equal incre
ments of load resulted in equal increments of the forward displacement of
the front surface of the shotcrete layer. The displacements were slightly
greater along the vertical center line of the shotcrete layer and decreased
toward the edges of the model. The shape of the displacement profiles, be
fore failure, was produced by the stresses imposed on the layer at the con
tact with the movable block. Since the tensile stiffness at the contact
between the shotcrete layer and the surface slabs is extremely high, the
relative displacement was almost null.
In the cases where diagonal tension failures occurred, the dis
placement of the shotcrete surface increased linearly with increasing load.
4-41
'
S-1
0 .-
50E ......... E
~ ;::1. l 00 I ......... ~ N .µ
s::: Cl) O 150 E Cl) u <O ,-0... Vl 500 .,...
-0
,-<O
~ 1000 0 s..
LL
1500
i
3 4
11 2.22 kN
(22.25kN)
e6,69 kN) 6000 1 bf to
5.59 kN) 8000 lbf
r4 Scale 2"07n.
Load
10,000 lbf (44.48 kN)
12,000 lbf (53.38 kN)
0
20
40
.-I
--..._ ______ ___.----14,000 lbf 60 _o
(62.28 kN) 00
400
600
FIGURE 4.29 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
.--.. . s::: .,...
<::I'" I 0 ,-......... .µ s::: Cl)
E Cl)
u <O ,-0. Vl .,...
-0
,-<O .µ s::: 0 s..
LL
S-2 <t.
3 ) ( 4 ) ( 5) (6) (7 ) ( ) 1~ Sca~e , j 20 ,n.
o_ Load 0
-----50 I- J- ......... ____/ 4000 l bf j20 . s::::
(11.79 kN) .,....
/ 6000 lbf <:::I'"
E 100 I- ~ " I
..J::> (?fi_ fiq kN) 40 0 I
;:l.
..J::> ..........
w +->
O 150 [ [ ~60 +-> s:::: s:::: a,
0 a,
E ---- 8000 lbf (35.59 kN i) E a, - (lJ
u - • :~ 10,000 lbf (44.48 kN) u n::I - • n::I ,-- • I ,--c.. I • , 12,000 lbf (53.38 kN) 200 c.. Ill 50 Ill .,.... .,.... -0 -0 ,-- ,--
.:3 100 400 n::I +-> s:::: s::::
0 0 ~ ~
LL LL
600
FIGURE 4.30 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-3 t.
---~.•· ··
cb (j) @G) 0 00 cb 0 r Scale 20 in. • I
0 Load 0
2500 l bf
50
----E .i::, ;:l
100 I ........
t .µ c:: (l)
150 E (l) 0 u n:, r-
( 11. 12 kN) ----5000 lbf j20 . c::
(22.25 kN) •,-
7500 l bf (33.37 kN) ,;j" I
10,000 lbf (44.48 kN) 40 0 r-
12,500 lbf (55.60 kN) 15,000 lbf (66.72 kN)J
.µ c:: (l)
--------- 60 Jo E (l)
u n:,
0. r-V'l
,,- 500 -0 200 ~
•,--0
r-n:, r-.µ
§ 1000 s...
400 .;3 c:: 0
LL s... LL
1500 600
FIGURE 4.31 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-4
0
50 ......... E ;:l.
~ ---- 100 I .µ ~ s:::: (J1
QJ E Q.)
0 u r'd -0. (,/) .,....
500 -c -r'd .µ
§ 1000 s...
LL.
1500
i
1/4" steel plate 1/4" steel plate
6 3 4 5 J ( 6 ) ( 7 ) ( ) ~ Sea le 20 in.
Load 0
~ .. ~ 2500 lbf ( 11 . 12 kN)
1250 lbf -120 ( 5. 56 kN)
1100 lbf --I 40 ( 4. 89 kN)
60 -----.---------- 1100 lbf (4.89 kN)
FIGURE 4.32 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
• I
0
200
400
600
. s:::: .,....
o:::r I 0 ,..... ----.µ s:::: QJ
E QJ u rd ,..... 0. (,/) .,.... -c ,..... rd .µ C: 0 s...
LL.
S-5
0
50
--E ;:i
100 -+=> .._.., I
-+=> +-> O'l C Q) E
0 Q) u ~ ,-0.. (/) .,...
500 -0 ,..... ~
+-> l 000 C
0 !,..
I.J....
1500
<t.
6 3 4 5 ~ Sea~= •I 20 "'.
Load 0
1000 lbf ( 4. 45 kN)
2000 lbf (8 .89 kN)
20
40
60
FIGURE 4.33 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
0
. C .,...
'<:I'" I 0 ,..... ..........
+-> C Q)
E Q) u ~ ,..... 0..
200 -~ -0
,..... ~
400 t
600
0 !,..
I.J....
S-6 't.
1/4 11 Steel plate II I H 1/4 11 Steel plate
~) l5 J l(iAJ.IU (7 J
41
?;''~'~ 5:~e 20 l n. ~ I
o_ Load 0 5000 lbf .--..
( 22. 24 kN) . s:: .,...
5Cl- I- ~ / ✓ \ ~ 10,000 lbf 20 rj-
( 44. 48 kN) I
E
E '\__/
~ 0 ;:1.
,--..___.. -
.i::,. l 00 40 .µ I .µ s::
.i::,. s:: QJ -...J QJ
E E QJ
.1 QJ
u - 15,000 lbf (66.72 ~RJ 3 ° u
~
E - ~
,-- --.::::::: .-0. I :;:::::::- 17,500 lbf (77.84 kN) 0.
Vl I Vl .,... 200
.,... -0 -0
! lOOt ~ ~400
~ .µ s:: 0 s..
LL.
600
FIGURE 4.34 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-7 <t.
·••!·· ~ -~
cb 0 CD G © © © © © ~ Scale 20 in. • I
Or- Load 0 1500 lbf
( 6. 67 kN) -20 .
50r- t- -- 2000 lbf C: ,,-
(8.89 kN) tj" -E
I ~ E 3500 lbf 0 I ;::l.
100~ 40 ,--
~ .......... (15.57 kN) 00 +' +-' C: 4500 lbf C: QJ 150 QJ E 0 (20.02 kN) 60 0 E QJ QJ u u (1j (1j
,-- ,--a.
200 a.
VI 500 VI ,,- ..... "'O "'O
,- ,-(1j
400 ~ t 1000 C: 0 0 s.. s..
LL LL
1500 600
FIGURE 4.35 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-8
0
50 ..-... E ;:::l.
~ ---- 100 I ~
.µ I.O C
QJ E O 150 QJ u ro
,--c.. Vl .,.... 500 -0
,--ro .µ
§ 1000 s..
l.J....
1500
i
5
1/4" Steel plate
~ Seale • I 20 in.
Load 0 400 1 bf ( 1 . 78 kN) 20
1000 lbf ( 4. 45 kN)
1500 : lbf (6.67 kN) 40
1500 lbf (6.67 kN) 60 -0
200
400
600
FIGURE 4.36 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
..-... . C .,....
tj" I 0 ,--
----+> s:: QJ E QJ u ro ,.... .. c.. Vl .,....
-0 ,-ro .µ C 0 s..
l.J....
S-9 i
-~ -~--
cb 0 00 © ©0 © @ r Scale I 20 . • in.
o_ Load 0 2500 lbf ( 11. 12 kN ........
50 l _ L -------- - _____....-:: 20 . --- • •::iooo lbf C
(22. 25 kN) •,-
<d° - t ~ 7500 lbf I 3. 100 0
~ {33.37 kN 40 ,-
j O 150
......... I
10,bOO lbf (44.48 kN) ...., 01 0
12,500 lbf f 55.60 kN~ 60 o i 15,000 lbf 6!472 kN 1 "
I 5of F - l J • 12,000 l bf ~ l l 312
I (failure) 200 'c.. Ill 180 208 370 200 80 •,-
"'O
,-
400 tO +' C 0
"" u. 600
FIGURE 4.37 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-10 't.
1/4" Steel plate __ !: II I H ~! ,_l/4" Steel plate J,· ··· ·e d
3 ) ( 4) { 5) (6) (7 ) ( ) ~ Seale I 20 in. '
o~ Load 0 1250 lbf
(5.56 kN) . C:
50L L '---- 20 •r-
2500 lbf tj"
( 11 . 12 kN) I 0 ..........
~ ~
...-E
40 ..........
;:::l.
100~ -+=- .......... .µ I C: u, .µ Q) _.
C: E Q)
O 150 60 Q)
E 0 u Q) cu u 3800 lbf (16.9 ·kN) ,-res c.. ,-
5000 lbf (22.25 kN) Vl c..
500 200 :; Vl 6250 lbf (27.8 kN) •r--0 7000 lbf (failure ...-
res ,-
31.14 kN) .µ res 400 C: .µ 1000 0 C: s.. 0 LL s..
LL 2320 1soo 1 I .J500
FIGURE 4.38 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-11
0
50
,,....._ E ;:::l.
~ ---- 100 I u, .µ N i::
QJ E QJ u ~ ,-Cl. V1
•,- 50 -0
,-~ .µ i:: 0
1000 ~
LL
1500
't.
1/4" Steel plate 1/4" Steel plate
0 4 5 6 1--4 Seale • I 20 in.
I a..c::::: •c.::::::::::: :=zs •==:::: :::::>" ::.:::::;a,a hYYU t0
2000 lbf ,20
(8 .89 kN)
3000 lbf (13.34 kN) 740 4000 lbf (17 .80 kN)
5000 lbf (22.25 kN) _J6Q
FIGURE 4.39 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
~o 200
400
i:: •,-
.;j-1 0 ,-
.µ i:: OJ E OJ u ~ ,-Cl. V1
-0
~ .µ i:: 0 ~
600 LL
S-12
0
50 ,--...
E ;:l.
100 ..__.. +=> I .µ
u, s:: w (I)
150 E 0 (I)
u ro -0.. (/)
500 •,--0
,--
ro
~ 1000 0 s....
LL
1500
t.
1/4" Steel plate l /4" Steel plate
CD 4 5 I Scale ~ 20 in.
0 •
1000 1 bf -t20 (4.45 kN)
1500 l bf _J40 ( 6. 67 kN)
7 60
FIGURE 4.40 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
• I
-0
:200
. s:: •,-
""1" I 0
.µ C (I) E (I) u rd
,--0. (/)
.,--0
,--
400 ~
00
C 0 s....
LL
S-13
0
50
~ l 00 I . u, ~·
O 150
500
1000
1500
i
1/4" Steel plate
4 5
1/4" Steel plate
6
•• II II II II II
h Scale I 20 in. "
I 1liE<.....: .......__ :::::::» O a::c:::::: :::,' :, 0 ,O
~
l 000 l bf ( 4. 45 kN)
3500 lbf --420 ( 33 . 37 kN)
10,000 lbf ~40 ( 66. 68 kN)
12,500 l ~f 1 .--==--- ( 55. 6 kN r-60
( 66. 72 kN)
FIGURE 4.41 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
0
200
400
600
S-14 t.
1/4 11 Steel plate 1/4 11 Steel plate
4 5 6 I~ Scale 20 in. • I
0 Load 1250 lbf (5.56 kN) .
50 ,......_ E ;::1.
----+'lo
+' 100 c::
I OJ U'1 E U'1 OJ
u o 150 rtl -,- r-r 0 0 ·----. 0. 0 (/) .,....
"C 500
2500 lbf 20 c::
( 11. 13 kN) .,....
-=:::I" I
5000 lbf 0
( 17. 80 kN 40 ,-
----5000 lbf +'
c::
(22.25 kN 60 OJ Jo E OJ
6250 lbf (27.81 kN) u rd ,-0.
200 (/) .,.... ,-rtl "C +' c:: 0 s.. 1000 LL
,-rtl
400 +' c:: 0 s..
LL
1500 600
FIGURE 4.42 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
S-15 t
1/4 11 Steel plate ' Steel plate
4 5 6 r s ca ~ e • I 20 1 n.
Load 0 Or- 2500 1 bf
( l 1.'l2 kN ---:-
5o 5000 lbf 20 -~ E (22.24 kN <:f" ~ 0
.i::- _. 100 7500 1 bf .::. 0-, ~ ( 33. 36 kN) 4o +-> ~ W C
E w w 150 E
~ o ~ ========== . 10,000 10 60
o ~ ~ '~ : ~ (44.48 kN) ';_ :;; 500 ~---- ~ 12,500 lbf 200 .:'! .-- (55.60 kN) -o
~ ------ r-~ ' 15 , 000 1 bf ( 66 . 72 kN ) 400 ~ ~ lOOO 7000 1 bf ( 31. 13 kN) ~
LL.
1500· • .....600
FIGURE 4.43 FRONT FACE DISPLACEMENT OF SHOTCRETE LAYER WITH RESPECT TO THE FLOOR
In these cases the adhesive force, Fa, was greater than F1, the force
required to induce a diagonal tension failure in the shotcrete layer.
Separation of the shotcrete from the surface of the slabs occurred in two
of these tests, Nos. S-1 and S-2, but was confined to a very narrow zone,
1-1/2 to 2 in. (3.81 to 5.as cm) wide on the inside edge of the fixed wall.
The initial loss of adhesion followed by the diagonal tension failure in
dicates that forces Fa and F1 were almost equal and both the adhesive
strength and diagonal tension strength were fully mobilized.
When diagonal tension failures occurred,no additional resistance
was offered by the shotcrete layers.
The second mode of failure, separation between the shotcrete
layer and the concrete slabs, was present in all the other tests. The in
duced adhesive stress exceeded the adhesive strength between the shotcrete
and the surface slabs before the level of stress in the layer reached the
diagonal tension strength of the shotcrete. The separation of the shotcrete
layer from the surface slab started at the movable block and progressed
toward the boundaries of the layer. However, in the absence of steel plates
the length of propagation of the failure surface was at least in part re
lated to the thickness of the shotcrete. In test No. S-5, when the thickness
of the shotcrete was 5.26 in. (13.4 cm), the failure propagated to the ends
of the layer. In test No.S-3, 2.18in. (5.5 cm) thick. it progressed 15.5 in.
(39.4 cm) to a point where the bending stresses in the inside face of the
layer exceeded bending strength of the layer and a failure occurred. In test
No.S-7, carried out on a 2.78in. (7 cm) thick layer cured only 7 hours, the
adhesive failure propagated 48 in. (122 cm) on one side but only 24 in.
(61 cm) on the other where a bending failure developed.
4-57
In the other tests, the shotcrete layer, after its separation
from the surface slab, acted like a simply supported beam uniformly loaded
in its center with end supports continuously moving apart to the limits
imposed by the steel plates. Immediately after the adhesion failure pro
pagated to the plates, the bending stresses produced by the ram exceeded
the bending capacity of the layer and two vertical cracks appeared on the
outside surface of the shotcrete along the contact between the movable and
fixed blocks. The progressive separation of the shotcrete layer occurred
so fast that the cracks appeared almost simultaneously with the adhesive
failure.
In all tests, separation never occurred between the shotcrete /
layer and the surface slab covering the movable block.
4.4.3 LAYER RESISTANCE VS t'OVABLE BLOCK DISPLACEMENT
The ram load and displacement were constantly monitored using an
x-y plotter. The results were plotted in terms of unit resistance, i.e.,
the ram load divided by the vertical 48 in. (122 cm) of contact between the
shotcrete layer and the fixed walls against the 11 net 11 displacement of the
movable block.
Three basic types of curves corresponding to the three different
structural behaviors were exhibited by the shotcrete layers (Fig. 4.20).
In the load range before failure, all the curves showed a very stiff and
linear relationship between the resistance of the layer and the relative
displacement of the movable block. Once failure occurred, different struc
tural behaviors of the shotcrete layer were observed as follows.
4-58
At load levels above 70 percent of the maximum layer resistance, a non
linear relationship developed in which rate of displacement increases
faster than the rate of load.
The profile of displacements along the shotcrete layer out from
the movable block depends mainly on the tensile stiffness between the
shotcrete layer and the surface slab. It also depends on the stiffness of
the shotcrete layer and to a lesser degree on the location of the lateral
restraints. The post-failure displacements of some of the shotcrete layers
occurred very rapidly and were not measured in tests represented by type l
and 2 curves (Fig. 4.20). In tests represented by type 3 and 3A curves,
displacements of the movable block were controlled so that the displacements
of the shotcrete layer could be observed. In four of the tests (test Nos.
S-4, S-8, S-9 and S-15) the shotcrete surface displacements were closely moni
tored thus allowing the deflective shape of the shotcrete layer and the prop
agation of the adhesive failure to be observed.
The deflected shapes of the failed shotcrete layers are very simi
lar to those of the mortar layers and resemble the deflected shape of a
simply supported beam (test No. S-4 - Fig. 4.32). In addition, the dis
placement obtained from dial gages placed against the center of the block
were nearly the same as those obtained from the LVDT in the ram for the same
load increments.
4.5 EVALUATION OF VARIABLES INFLUENCING THE STRUCTURAL BEHAVIOR Of THE LAYER
Each of the 16 shotcrete layer tests was carried out to evaluate
4-59
the effect of a particular variable on the structural behavior of the
layer. The variable to be compared in a given set of tests is summarized
in Table 4.5. The influence of variables on the structural behavior will
be discussed in the following section and will be described in terms of
their effect on the observed modes of failure and the resistance and dis
placement of the movable block.
4.5. 1 LATERAL BOUNDARIES
The effect of lateral boundaries on the behavior of the shotcrete
layer can be seen by comparing test Nos. S-3, S-4, S-9 and S-10. Test Nos.
S-3 and S-9 were carried out with shotcrete layers having approximately the
same thickness and strength, however in test No. S-9 the lateral boundaries
of the layer were located 4 ft (121.9 cm) apart, while in test No. S-3 steel
plates were not used. In both tests, the same mode of failure involving
separation of the shotcrete layer from the surface slab was observed. The
maximum resistance of both shotcrete layers and the slope of the load
displacement curve were almost the same. After the peak load was reached
in test No. S-3~ the resistance dropped off rapidly after a small displace
ment (0.04 in.; 1.02 mm) of the movable block. In test No. S-9, however,
the residual resistance decreased gradually (dashed line - Fig. 4.44) and
finally reached zero after a relatively large (1.0 to 1 .5 in.; 25.4 to 38.1
mm) di splacement of the movable block. The ductility of the layer having
lateral restraint was approximately 3 times that without restraining bounda
ries.
Figure 4.45 shows the resistance - displacement relationship for
4-60
TABLE 4.5
VARIABLES COMPARED IN THE SHOTCRETE LAYER TESTS
Test no. S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-10 S-11 S-12 S-13 S-14 S-15 S-16
S-1 R S-2 T T S-3 S-4 A T S-5 T T T S-6 A S-7 M
.j:::,
S-8 M A I 0) _,
S-g L s-10 L A S-11 M
S-12 M A S-13 T T T T S-14 T T T T T S-15 Re Re Re S-16 Re Re Re
LEGEND: R = Repeatability T = Thickness value A = Adhesion surface characteristics M = Mortar strength L = Lateral boundary conditions
Re = Reinforcement
Movable block displacements (mm)
0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20 . 0 I I I I I I I I I
90 500
80 C: .... E - -'+- z .o 400 ~
S-3 70 .µ
.µ u u rtS rtS .µ .µ S-9 C: C: 0 0 0 u u
'+-'+- 0 0 300 ..c:
.j::,, ..c: 0 .µ .µ c:n
I C7l C: 0-, C: OJ N QJ ,......
0 .µ
.µ
" .... .... '
C: C: :::, ::, 200 ' s... s... ' OJ OJ ,..._ 30 c.. c.. .._ ..._ OJ QJ u u -- C: C: -- rtS rtS .µ .µ
0 VI V) .... .... 100 A
V, V) OJ QJ 0::
ei:::
10
01 I I 01 - _JO, 0 100 200 300 400 500 600 700 800
Movable block displacements (10-3 in.)
FIGURE 4.44 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
Movable block displacements (mm)
0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0
I I I I I I I I I 500
I I I I I I I
0
-. - -----C: E .,... ;;::- 400 -70 z: ..c .:,,,:
r-......... +->
+-> u u 60 "' ~ +->
+-> C:
C: 0 0 u
~ u 300 S-10 '+-
'+- 50 0 I
O'l 0 .s::. w +-> .s::. O') +-> O') C:
C: Cl)
QJ 40 ,-
r- +-> :!: 200
..... C:
C: :::,
::, s... s... 30 Cl)
(1J c.. Q. 0 Cl)
(1J u u C:
20 "' C: +-> "' 100 Vl +-> Vl
..... ..... Vl
Vl Cl)
Q) 0:: 0:: 10
0 0 0 300 400 600 700 800
Movable block displacements (10-3 in.)
FIGURE 4.45 UNIT LENGTH RESISTANCE VS MOVABLE BLOCK DISPLACEMENTS
~
test Nos. S-4 and S-10 in which steel plates were spaced 8 ft (243.8 cm) and
4 ft (121.9 cm) apart, respectively. No difference was observed in the mode
of failure of these 2 layers. The difference in the maximum resistance of
the layers was probably caused by a greater adhesive strength along the con
tact between the layer and the surface slab in test No. S-10. The greatest
difference in the structural behavior of the two layers can be seen in their
residual resistances. Where the steeJ plates were spaced 8 ft apart (test
No. S-4), the residual resistance. of the layer did not exceed 50 lbs/in.
(8.8 kN/m) and was reduced to zero for a displacement of 0.2 in. (5.1 mm).
On the other hand, where the steel plates were located 4 ft apart (test No.
S-10), the residual resistance of the layer reached 200 lbs/in. (35 kN/m) ,
at 0.02 in. (0.51 mm) displacement and decreased to zero only after the
movable block had displaced an additional 0.8 in. (20 mm). The difference
in the residual resistance of the two layers was not only caused by the
location of the end restraints but also was related to the greater thickness
(1 in.) of the shotcrete layer in test No. S-10.
From the results of these tests, the following conclusions with
respect to the structural behavior of the shotcrete layers were drawn:
1. The initial mode of failure and the maximum resistance
of the shotcrete layers were not affected by the presence
of steel plates within l ft (30 cm) of the movable block.
2. Observed variations in the maximum resistance of some
layers were caused by differences in adhesive strength
and not by the differences in the location of the lateral
restraints of the layers.
4-64
3. Both the load carrying capacity and the displacement
of the layer after adhesion failure were affected by
the position of the steel plates.
4.5.2 THICKNESS OF THE LAYER
Variations in the mode of failure and in the maximum and residual
resistances of the layers were produced by differences in shotcrete thick
ness. For shotcrete layers having thicknesses ranging between l. l in. and
1.9 in. (26.9 mm to 47.2 mm) and good shotcrete-slab bonds, diagonal tension
failures occurred in the shotcrete layers (Fig. 4.46). The maximum resistance
of the layer was directly related to the thickness of the shotcrete. In all
of these tests the residual resistance of the layers rapidly decreased to
zero.
The mode of failure changed primarily to separation of the shot
crete layer from the surface slab when the thickness of the shotcrete reached
approximately 2.2 in. (5.53 cm) as seen in test No. S-3. The maximum resist
ance offered by the layer increased slightly as well as the displacements of
the movable block relative to the tests in which diagonal tension failure
occurred. Further increases in thickness, at least up .to 5.26 in. (13.4 cm),
did not affect the overall mode of failure nor the maximum resistance of the
shotcrete layer.
For test Nos. S-4 and S-6, in which filament tape was used to reduce
shotcrete-slab bonds, the shotcrete thickness had no effect on the failure
mode or the maximum resistance of the layer. This would be expected since a
diagonal failure could not develop in layers having loose bond unless restraints
were placed close to the movable block.
4-65
Movable block displacements (mm)
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 5.0
I I I 0
500
80 -. C: -.,....
........ 4--.0
e ........ 70 z
~
--- ,--- -+-'
+-' u u
rd rd +-' C:
60 +-' C: 0
0 u u
4--0 ..,.
4--0
50 ..c: I ..c:
O"I +-' O'I C'l
+-' C'l C:
C: QJ (l) ,--
,--
+-' .,.... 40 +-' I I ....
C: S-13
C: ::::, ::::,
s... (l)
s... 30 QJ
0. 0.
...... (l) QJ u
u C: C: rd +-'
rd 20 +-'
VI VI .... .,.... VI VI (l)
0:::
QJ
~ 10
20 40 60 80 100 120 140 60 0
Movable block displacements (10-3 in.)
FIGURE 4.46 UNIT LENGTH RESISTANCE ·vs MOVABLE BLOCK DISPLACEMENTS
In tests where the shotcrete-slab bond was low and the thickness
of the layer was high (test No. S-10) the maximum resistance of the layer
was controlled by the bending capacity of the layer rather than by the ad
hesive strength. As the thickness increases ,the bending stiffness of the
layer increases and thus provides an increase in bending strength. In test
No. S-10 the bending capacity was governed by both the thickness (3.1 in.)
and the spacing of the steel plates (4 ft).
The following conclusions were drawn regarding the influence of
the layer thickness in the structural behavior:
l. For a good shotcrete-slab bond (roughened surface and
7-day curing), the primary mode of failure changes from
diagonal tension to adhesion as the thickness of the layer
increases above 2 in. (5.1 cm). Once this thickness is
reached, further increases do not alter the mode of failure.
2. For diagonal shear failures, the maximum resistance of the
layer is directly proportional to layer thickness. For
adhesive failure the thickness does not affect the maxi
mum resistance unless the shotcrete-slab bond is poor
and the layer has a greater bending capacity than adhesive
strength. Where diagonal failure occurred the maximum re
sistance ranged from 150 lbs/in. (26 kN/m) for a 1-in. (2.5 cm)
thick layer to 320 lbs/in. (56 kN/m) for a 2-in. (5.1 cm) layer .
3. The residual resistance of the shotcrete layer increased
with increasing shotcrete thickness. A residual resis
tance of 30 lbs/in. (5 kN/m) was observed in test No. S-8
4-67
l
having a thickness of 3.0 in. (7 .5 cm), while in test
No. S-6 the resistance of the 4.7 in. (11.9 cm) layer
was 50 lbs/in~
4.5.3 ADHESIVE SURFACE CHARACTERISTICS
Changes in the structural behavior of the layer resulting from
differences in shotcrete-slab adhesion can be seen by comparing pairs of
test Nos. S-3 & S-4, S-5 & S-6, and S-9 & S-10 performed at 7 days. The
differences in adhesive strength for each pair of tests was obtained by
using a roughened surface (representing good bond) and a surface covered
with tape (poor bond). The same mode of failure, separation of the shot
crete layer from the surface slab, was observed in all the tests; however,
the maximum resistance was strongly influenced by the adhesive strength
developed between the shotcrete and the slab. The maximum resistance of
layers having poor shotcrete-slab bond were approximately 20 percent of
those in which the shotcrete was placed against roughened contacts (Figs.
4.22, 4.23 and 4.25). The higher resistance obtained in test No. S-10
relative to tests S-4 and S-6 was caused by localized penetration of shot
crete in the slots surrounding the movable block. Although maximum re
sistance was strongly affected, the residual resistance was not sensitive
to surface adhesion when lateral restraints were present.
Similar results were obtained for the 7 hr tests (test Nos. S-7 &
S-8 and S-11 & S-12). However, the maximum resistances of the layers having
poor bond was 30 to 40 percent of the values obtained for the wire brushed
surfaces. The residual resistance of the 7 hr tests were the same for
4-68
both taped and untaped surfaces where the restraints were placed at the
same location. Based on the test results, the influence of surface ad
hesion on the structural behavior of the shotcrete layers are summarized
below:
1. For shotcrete layers greater than 2 in. (5 cm), the
failure mode is not changed by bonding conditions of
the surface. However, diagonal tension failures can
develop when shotcrete thickness is less than 2 in .
(5 cm) and shotcrete-slab bond is good. These failures
cannot develop when bond is poor, independent of the
thickness of the layer.
2. Poor contact bond can reduce the support capacity of the
layer as much as 60-80% relative to layers having good
shotcrete-slab bond. The greater reductions occurred
in shotcrete layers having higher strengths (7 days).
3. The residual resistance of the layer was the same for
both good and poor shotcrete bond strengths when lateral
restraints were present at the same locations relative
to the movable block.
SHOTCRETE STRENGTH
The variations in the adhesive strength caused by differences in the
time of curing were studied by comparing results of test Nos. S-3 & S-7, S-5 &
S-11 ,S-4 & S-8,S-6 & S-12. The strength of the shotcrete layers does not affect
the mode of failure (separation of the shotcrete layers from the surface slabs),but
4-69
bond. It had the greatest effect on the roughened
surfaces while the taped surfaces were not as sensi
tive because the smoothness and impermeability of
the tape tended to control the adhesive strength.
When the bond is good ,shotcrete 7 hours old has
approximately 1/5 the support capacity of a comparable
7-day old layer. However, with poor bond only a slight
increase in the capacity of the layer occurs (30-50 lbs/
in.) between 7 hours and 7 days.
3. The residual resistance of the layer is directly pro
portional to the curing time. For the 7 hr test, the
residual resistance of the layer was 1/4-1/5 of the
value at 7 days.
4.5.4 USE OF REINFORCEMENT
The influence of steel fiber reinforcing in the shotcrete layers
can be seen by comparing test Nos. S-4 and S-16. The layers in these tests
are very similar except that in test No. S-16, steel fibers, 0.01 in. x
0.022 in. x l in. (0.025 cm x 0.056 cm x 2.54 cm), were added to the shotcrete
before gunning. The presence of fiber produces no significant increases in
the maximum resistance of the shotcrete layer (Fig. 4.48). However, both the
residual resistance and ductility were greatly increased when fiber was pre
sent in the layer.
Residual resistance of the reinforced and nonreinforced shotcrete
layers placed on roughened concrete cannot be compareddue to different lateral
4-72
500
. s:: •,--...... 4-.0 400 ,--
----.µ u .,, +-' s:: 0 u
4- 300 0 .i::,. I .c
........ +-' w Ol
s:: (1,)
,--
.µ •r-s:: 200 ::I
s... (1,) a. (1,) u s:: .,, +-' (/) 100 •r-(/)
(1,) 0::::
0
Movable block displacements (mm)
0.25 0.50 0.75 1.00
S-16
300 400
Movable block displacements FIGURE 4.48 UNIT LENGTH RESISTANCE VS MOVABLE
1.25 1.50
500 600 ( -3 10 in.) BLOCK DISPLACEMENTS
l. 75 2·~00 ., 90
80 ,-... E -...... :z
70 .=.. +-' u .,, +-'
60 s:: 0 u 4-0
50 ..s:: +-' Ol s:: (1,)
,--
40 +-' •r-s:: ::I
s... 30
(1,) a. (1,) u s:: .,, +-'
0 (/)
•r-(/)
(1,) 0::::
10
JOO 800 0
boundary conditions of the layers. However, differences in the adhesion
surface conditions do not alter the residual resistance characteristics
of the layer. From the above mentioned results it can be concluded that:
1. The use of fiber-reinforced shotcrete does not
change the mode of failure nor increase the maxi
mum resistance of the layer as compared with con
ventional shotcrete under similar conditions.
2. After adhesion fail~res occurred, the steel fibers
increased the ductility of the layer and provided
greater post-crack resistance.
4.5.5 REPEATABILITY 'OF THE TEST RESULTS
The repeatability of the test results was checked by performing
two tests having essentially the same conditions (test Nos. S-1 and S-2). Even
though a relatively small difference existed in the thickness of the layers,
±0. 1 in. (±.25 cm), the same structural behavior was observed and the maxi
mum resistance of the layers was very similar. In both cases the residual
resistance decreased rapidly to zero after the adhesion failure. It can be
concluded then, that the shooting and testing conditions can be controlled
accurately enough to reliably reproduce test results.
4-74
CHAPTER 5
SUMMARY AND CONCLUSIONS
5. 1 MAXIMUM RESISTANCE OF THE LAYER
In the tests where failure primarily involved separation of the
shotcrete layer from the slab (adhesion failure), the maximum resistance
was directly proportional to the adhesive strength along the shotcrete-
slab contact and was almost independent of shotcrete thickness. The dashed
band in Fig. 5.1 shows the linear relationship between the maximum layer
resistance and its adhesive strength. In these cases the maximum resistance
was equal to F0, the resultant force of the adhesive strength developed be
tween the shotcrete and the surface slabs. The relatively high resistance of
the layer in test No. 9 was caused by the presence of shotcrete in the slots
surrounding the movable block.
In the tests in which diagonal tension failures occurred, the
maximum resistance was directly proportional to the thickness of the layer
and to the shotcrete strength. The measured resistances coincided very
closely with calculated values of F1 , which is the shear force required to
induce a diagonal tension failure in the layer. Values of F1 were calcu
lated assuming the diagonal tension strength of the shotcrete equal to
2/f'c (where f'c is the compressive strength of the shotcrete) and are shown
by the horizontal dashed lines in Fig. 5.1. In tests involving adhesion
failures, the calculated values of F1 were always greater than the actual
maximum resistance of the layers. On the other hand, the calculated shear
forces (F1) were always less than or equal to the maximum resistance of layers
5-1
Adhesive strength (KPa) 0 200 400 600 800 1000 1200 1400
160 I I I I I I I I
35 ----------,..----------------
140 --------------- @
30
® 120
25 ----------------------- ®
100
20 e9 @
,,....._ z: Vl
.:=. 80 0.. •,-~
X l'tl E X
0... l'tl
0... E 15
60
10 40
20 5
0 40 80 120 160 200
Adhesive strength (psi)
FIGURE 5. l MAXIMUM RAM LOAD VS MEASURED ADHESIVE STRENGTH
5-2
in which diagonal tension failures occurred. In these cases the values of
F0 given by the dashed band were much greater than the actual maximum re
sistance offered by the layer.
The structural behavior of the layers depends on the mode of fail
ure which is controlled primarily by thickness and bond of the shotcrete.
For any given layer when the diagonal tension strength is greater than the
adhesive strength,a separation of the shotcrete layer occurs and the maximum
resistance offered by that layer is given by the force F0. On the other
hand, when the diagonal tension strength is less than the adhesive strength,
a diagonal tensile failure occurs and the maximum resistance offered by the
layer is given by the value of F1. This structural behavior corresponds
exactly to the one proposed in the model of Chapter 3.
5.2 RESIDUAL RESISTANCE
Visual observations together with the displacement measurements
indicate that the shotcrete layers behave as simply supported beams uni
formly loaded in their center sections after an adhesive failure develops.
The load carried by each shotcrete layer acting as a simply sup
ported beam (Fig. 5.2) was calculated using the geometric characteristics
of the layers, shotcrete strength and distance between the lateral restraints
and the movable block. The values of the layer properties used in the cal
culations as well as the calculated and measured residual loads of each
layer are summarized in Table 5.1.
Except for test Nos. 9 and 10, the measured and calculated resid
ual loads assuming a simply supported beam are very similar although the
5-3
• uunm w ~
L _, L
a) SIMPLY SUPPORTED BEAM
~ UIUUU ~ ~ I~ _, L
b) DOUBLE CANTILEVERED BEAM
FIGURE 5.2 BEAM MODELS USED IN RESIDUAL CAPACITY CALCULATIONS
5-4
measured value is usually slightly higher than the calculated value. The
difference between the calculated and measured residual resistance values
was probably provided by the steel plates which served as a restraint against
rotation at the extremes. It must be pointed out that the residual resist
ance values measured were much closer to the lower limit obtained assuming
a simply supported beam than the upper limit calculated assuming develop
ment of a double cantilever beam (Fig. 5.2 (b); Table 5. 1). Calculated re
sidual resistance values assuming cantilever action at the beam supports
were 5 to 10 times higher than the actual values of residual resistance.
The double cantilever beam did not develop because of the flexibility of
the steel plates and their supports. The closer the restraints were to the
movable block,the more the layer tended to act as a cantilever beam. For
test Nos. 9 and 10 in which the steel plates were located 1 ft (30.4 cm)
from the movable block, the measured values of the residual load were 4
times higher than the value estimated for a simply supported beam. After
large displacements (1 in.; 2.54 cm) of the movable blocks, the load de
creased to 2200 lbs (9.79 kN); this was only twice the calculated value.
5.3 GENERAL CONCLUSIONS
Results of the tests carried out on the mortar and shotcrete
layers confirm the validity of the model of behavior of thin linings on flat
tunnel surfaces given in Section 3.3.
l. Two modes of failure were considered in the model: separa
tion of the shotcrete layer from the surface slab and
diagonal tension failure in the shotcrete layer. Both
5-5
2.
modes were observed in the testing program; their
occurrence depended on the relative value of forces Fa
and Fl .
The max i mum resistance offered by the layer depends on
t he mode of failure and its magnitude is given by the
smaller of the forces F0 and F1. When separation of
the shotcrete layer occurs, the maximum resistance is
directly proportional to the maximum adhesive strength
per unit area of contact. For variations in the adhe
sive strength from 180 psi (1241 .l kPa) to 20 psi
(137.90 kPa), maximum resistance per unit length of the
movable block contact ranged from 400 lbs/in. (70.05
kN/m) to 50 lbs/in . (8.76 kN/m).
If a triangular distribution of the adhesive strength
between the shotcr ete layer and the surface slab is
assumed, the distribution of stress does not extend be
yond a few inches ( 2 to 4 in.; 5 to 10 cm) away from
the movable block. The load applied through the movable
block is transmitted by the shotcrete layers along two
narrow (2 to 4 in.; 5 to 10 cm - wide) bands parallel to
the contact between the movable and the fixed walls.
Test results indicate that variations in the surface ad
hesive conditions (wire brushed or taped surfaces), or
in layer properties (thickness, strength) does not sig
nificantly change the width of these bands. Theoretical
5-6
considerations, i.e., beam on elastic foundation theory,
would predict that the area over which adhesive strength
is distributed would remain constant since the stiffness
in bond is much greater than the flexural stiffness of
the beam.
3. The capacity of the shotcrete layer in diagonal tension
depends on the thickness of the layer and in shotcrete
strength while in adhesion it is governed by the surface
characteristics and shotcrete strength (as affected by
curing time).
4. After reaching its maximum resistance,the structural
behavior of a conventional shotcrete layer depends
mainly on the mode of failure, the adhesive surface
conditions, the lateral boundaries of the layer, and
the strength and stiffness of the shotcrete. When
separation of the shotcrete starts, the adhesive fail
ure propagates away from the movable block depending
on the thickness of the layer and the slab surface
characteristics. The length of propagation of an ad
hesive failure for wire-brushed surfaces varied from
48 in. (120 cm) for a 5.26 in. (13.5 cm) layer to 15.5
in. (39 cm) for a 2.18 in. (5.54 cm) - thick layer.
When the adhesive strength is low, the failure propa
gated all the way out to the boundaries of the layer
independent of layer thickness.
5-7
When steel plates were present, the adhesive
failure was terminated at the plates and the shot
crete layer acted as a simply supported beam. The
residual capacity of the layer varied with the spacing
between plates and the thickness and strength of the
shotcrete. When plates were located 4 ft (122 cm)
apart the residual resistance of the layer was 110 lbs/
in. (10.5 kN/m) while an 8 ft (244 cm) spacing pro
duced a residual resistance in similar shotcrete layers
of 60 lbs/in. (5.7 kN/m). The flexural strength and
thickness both govern the load carrying capacity of a ,,
beam. In tests where the restraints were spaced 8 ft
apart, an eight-fold change in strength produced a
two-fold change in the residual resistance of the
layers (60 lbs/in. to 30 lbs/in., respectively). The
residual capacity of the layer varied with the spacing
between the steel plates. When the plates were located
4 ft (120 cm) apart the residual resistance of the layer
was 110 lbs/in. (19.3 kN/m) while an 8-ft spacing pro
vided a residual resistance of 60 lbs/in. (12.5 kN/m).
5. No residual resistance was observed in shotcrete layers
that failed initially in diagonal tension. Fiber rein
forcement increases both the residual resistance and
ductility of a shotcrete layer. The residual resistance
of fiber-reinforced shotcrete remained constant for
5-8
displacements of the movable block of up to O,ff in.
(2 cm). These displacements were approximately 5 times
greater than the residual displacements of similar
non-reinforced layers. A rate of loading does not
appear to have a significant effect on the maximum
resistance of the layers. For changes of 2 lbs/sec
to 5000 lbs/sec the layers showed a variation ±5 lbs/
in. which is less than the variation between similar
tests run at the same rate of loading.
RECOMMENDATIONS
1. The range of adhesion tested in this program is believed
to be fairly representative of the range of values en
countered in the field (Cecil, 1970 and Bortz and Singh,
1973). Values of the adhesive strength between shotcrete
layers and typical rock surfaces from different rock types
should be investigated to aid in predicting shotcrete-rock
bonding conditions in the field.
2. Considerable differences in modes of failure and shotcrete
resistances are expected for geometries other than a
planar configuration of movable blocks and adjacent blocks.
Such tests are to be carried out as a second stage of this
investigation.
3. The support capability of fast-setting (reg-set) cement
should be investigated.
5-9
4. A numerical model simulating the structural behavior of
the layers should be used to conduct a parametric study
of the main variables which affect layer resistance.
The results obtained from the mortar and shotcrete tests
would first be used to verify the numerical model. Once
the model is verified, it can be used to establish the
effect of the main variables having values different from
those used in the tests on the resistance of thin shot
crete layers. Such a modeling could be done using a finite
element technique where viability has already been sub
stantiated (Jones, 1975).
5-10
REFERENCES
Cecil, S. 0., 11 Correlations of Rock Bolt-Shotcrete Support and Rock Quality Parameters in Scandi navian Tunnels, 11 Ph.D. Thesis, University of Illinois, Urbana, Illino is (1970).
Cording, E. J., "Measurement of Displacements in Tunnels, 11 Proceedings, Second International Congress of the International Association of Engineering Geology, 2 :VII-PC-3. l - VII-PC-3.15, Sao Paulo, Brazil (1974).
Cording, E. J. and Mahar, J. W., 11 The Effect of Natural Geologic Discontinuities on Behavior of Rock in Tunnels," Proceedings, Rapid Excavation and Tunneling Conference, San Francisco, Vol. l, pp. l 07 -138 ( 197 4) .
Cording, E. J., "Geologic Considerations in Shotcrete Design, 11 Use of Shotcrete for Undergroudn Structural Support, ASCE and ACI SP-45, pp. 175-199 (1974).
Craig, L. Curtis and Brockman, L. R., 11 Survey of Tunnel Portal Construction at U.S. Army Corps of Engineers Projects, 11 Symposium on Underground Rock Cha mbers, Phoenix, pp. 184-185 (1971).
Jones, R. A. and Mahar, J. vJ., "In strumentation to Monitor Behavior of Shotcrete Support Systems, 11 Use of Shotcrete for Underground Structural Support, ASCE and AC! SP-45, pp. 297-319 (1974).
Parker, H. W., 11 Current Field Research Program on Shotcrete, 11 Use of Shotcrete for Underground Structural Support, ASCE and ACI SP-45, pp. 330-350 (1974).
Peck, R. B., Hendron, A. J . and Mohraz, B., 11 State of the Art of SoftGround Tunneling, 11 Proceedings, North American Rapid Excavation and Tunneling Conference, AIME, l :259-286.
R-1
APPENDIX A
This appendix contains a plate in which the principal character
istics and dimensions of the different load-applying rams components are
shown. Various cross-sectional areas along and across the ram axis, ac
companied with explanatory descriptions, are also shown in this plate.
A-1
);:, I
N
APPENDIX A
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APPENDIX B
The roughness of the concrete slabs was measured to compare the
different surfaces used in the mortar and shotcrete tests and for future
comparison with the roughness of actual rock surfaces.
A cold rolled steel surface was used as a standard to compare
different slab surface conditions.
Surface roughness was measured with a device designed to measure
the vertical relief along the surface of the slab minimizing damage to the
irregularities and thereby reducing chances for erroneous results (Fig. B-1).
This device consists of a base, a rotating arm and a contact needle. The
base of the instrument rests on three legs placed on the surface of the
sample. The length of each leg is adjustable so that the base can be lev
eled. The base support remains stationary while the arm, which contains
the sensing element, rotates about the centoidal axis.
The rotating arm is attached to the base on one end and holds the
contact needle on the other. The contact needle is located 10-1/2 in. (26.7
cm) from the axis of rotation. When measuring the roughness of a sample,
the arm is rotated slowly and the needle is maintained in continuous contact
with the surface. The needle is vertically displaced by the undulations on
the surface of the sample. This vertical displacement causes a corresponding
deformation in the cantilever arm. A strain gage mounted on the arm measures
the strain induced on its top caused by the deflection of the needle. A
linear relation exists between the deflection and the recorded strain.
The results of the roughness measurements are plotted directly on
B-1
FIGURE B-1 ROUGHNESS MEASURING DEVICE
an x-y chart recorder. The instrument is calibrated and appropriate scale
factors obtained so that the actual rotational and vertical displacements
can be determined. The horizontal scale factor isl in. equals 2.2 in. of
arc distance and the vertical factor isl in. equals 0.0125 in. of vertical
displacement.
Measured surface roughness of the cold rolled steel and typical
rough and smooth slabs are shown in Figs . B-2, B-3 and B-4, respectively.
Two main characteristics of the slab roughness were detected: 1) pits and
2) bumps. Pits are crevasses on the surface which have extremely small
widths but are very deep. Bumps are surface discontinuities which have
widths of considerable extent in comparison with pi ts. They usually have
second order features on the roughness plots.
B-2
Distance along 180° arc (cm)
0 10 20 30 40 50 60 70 80 90
125
3.0
1001 ' l ,2.5
- ...--..
s:: .... 2.0 E (Y) E I -0 75 r- VI - VI co Q)
I VI s:: w VI ..c QJ O') s::
1.5 :, ..c 0 O') ~ :,
0 O'.'. 50
I I I 1.0
25 0.5
0h 4 ~ 1~ 11l5 2
10 ~4 2
18 ~2 • 0
Distance along 180° arc (in.) FIGURE B-2 Test l (11/4/74) Cold rolled steel (very smooth)
Distance along 180° arc (cm)
0 10 20 30 40 50 60 70 80 90
125
3.0
100 I I } I \ ft.A.... I 72.5 -.
C: .... M r ( 2.01 I
~ 75 --------c::o Vl I +'> Vl
~ Vl
VI Q) Cl) C: C: 1.5 -§i .r:::. OI ::::, ::::, 0 0 ex:
o::: 50
- I .l \ I I J,.o 25
0.5
0 ~o---~4----s"-----, .... 2----,6~---2.L.o----24'-----.1.28 ____ 3.1..2 __ ___, 0
Distance along 180° arc (in.) FIGURE B-3 Test 1 (11/12/74) Mid-north finjshed side
- Distance along 180° arc (cm) 0 10 20 30 40 50 60 70 80 90
125
3.0
,oo I I 72.5
--· ....... . C: .,....
2.0 ----E M E .........
I 0 75 ,.....
co ......... V1 I V1
01 V1 Cl)
C ..c:
V1
1.5 Ol Cl)
:::, C:
..c: 0
0::: O'>
~A.ti-:::, - -0 50 0::
I I ~ I I 1.0
I I '- I I -25
I I ~-. I I .5
0 ~ t ~ k , ~ 116 2b 24 2~ J:5 '
0
Distance along 180° arc (in.) FIGURE B-4 Test 3 (11/11/74) South top form side
-
APPENDIX C
Tensile tests to measure the adhesive strength between the shot
crete and the surface slabs were carried out on samples cut from the model.
The size of the samples and the sampling method have already been described
in Section 4.3.3
EQUIPMENT USED IN THE TENSILE TESTS
The equipment used to perform the tensile tests is shown in Fig.
C-1. The sample was attached to the MTS loading machine shown in the center
of the picture. The tensile load was applied at a uniform rate and was elec
tronically controlled using the console shown on the right side of the loading
machine. Deformations were measured across the shotcrete-slab contact using
MTS strain gages. The loads and corresponding displacements were continuously
monitored on a chart recorder.
Figure C-2 shows a close-up of the sample in the loading position.
Each side of the sample was connected to the loading machine by means of
steel plates and a clamp which was welded to a double joint firmly held in the
loading head of the machine. Each clamp was provided with a set of screws
that exerted pressure on the steel plates in contact with the sample. This
arrangement plus careful sample preparation produced a relatively uniform
load with no noticeable eccentricity and did not allow slippage along the
grippers. The strain gage used to measure axial deformation was placed so
that its reference points, located 1/2 in. (1.25 cm) apart, bridged across
the shotcrete-surface slab contact (Fig. C-2). Although some samples failed
C-1
FIGURE C-1 FRONT VIEW OF THE TESTING DEVICE AND / MONITORING SYSTEM
fIGURE C-2 SAMPLE ATTACHING SCHEME AND GAGE MEASURING STRAIN ACROSS THE CONTACT
C-2
' t
•
along weaknesses (laminations) in the shotcrete, most failures occurred
along the shotcrete-slab contact (Fig. C-3).
FIGURE C-3 FAILED ADHESIVE TEST SAMPLE
C-3
TABLE C-2
SUMMARY OF ADHESION-TEST RESULTS
Test no. Sample Test Hours between Hours of no. hours cutting & testing curing
Adhesion value psi (MPa) Remarks
S-9 & S-10 T-lA* 144 0 144 144.7 (1.0) Cured in crane bay
T-2A* 144 0 144 ' 164.4 (1.13) Cured in crane bay
T-3A* 144 0 144 142.6 (0.98) Cured in crane bay
T-4A* 144 0 144 160.0 (1.10) Cured in crane bay
T-5A* 144 0 144 158.8 ( 1 . 09) Cured in crane bay n I
O'\ I = 770. 5
Avg= 154.0 (1.06)
* Samples obtained from center section, tested on June 4, 1975
-TABLE C-3
SUMMARY OF ADHESION-TEST RESULTS
Sample Test Hours between Hours of Adhesion value Test no. no. hours cutting & testing curing psi (MPa) Remarks
S-7 & S-8 S-1 7 0 24 86.8 (0.60)
S-2 7 0 24 l 08. l (0.75)
S-3 7 0 24 92.3 (0.64)
S-4 7 0 24 73. l (0.50)
("") S-5 7 0 24 83.9 (0. 581 I .......
S-6 7 0 24 65.3 (0.45)
S-7 7 0 24 73.4 (0.51)
S-8 7 0 24 87.6 (0.60)
S-9 7 0 24 111. 8 (0.77)
S-10 7 0 24 40.7 (0.28)
E = 823
Avg= 82 ( 0. 57)
--
TABLE C-4 ---
SUMMARY OF ADHESION-TEST RESULTS
Sample Test Hours between Hours of Adhesion value Test no. no. hours cutting & testing curing psi {MPa) Remarks
S-11 & B2 7 24 8.4 (0.06) S-12
C2 7 24 81.2 (0.56)
D2 7 24 38.6 (0.27)
E2 7 24 15 . 4 (0.11)
-- ('") I F3 7 24 7.2 (0.05) co
Excluding B2 & F3; I = 135. 2 (0.31)
Avg= 45
-
Axial displacements (µm)
0 2.5 5.0 7.5 10.0 12.5 15.0 17. 5 20.0
6
1250 ----r------,r-----,----,----,-----,----,---7
5r 100
\ ,oooL ( Sample C 2 Sectional area= 5.20 in.
I I I I 4
I 750
........ ........
~ 3 Vl
.Cl ,--
n ----I -0 <..O '° -0
0 <ti .....J 0
.....J 500
2
250
0 Ou...---....1..----~-----'-----...___....;;;;:::....__,, ____ -'----__,j-------' 0 l 2 3 4 5 6 7 8
Axial displacements (l0-4 in.)
FIGURE C-4 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS
Axial displacements (µm)
0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 --t
6
1250---------,-----,------r-----,-----.---,---7
5
I 1000 S-9 T
I Sectional area= 3.93 in. 2
4
~ , ........ .750 .::,,t. Vl
----- ..0 n -0 3 ~ I __, ~
0 0 ,~ _J
0 _J
500 I
2
250
0 l 2 3 4 5 6 7 8
Axial displacements (10-4 in.
FIGURE C-5 LOAD VS CONTACT DISPLACEMENTS RELATIONSHIP OBTAINED FROM ADHESIVE TESTS
EFFECT OF SAMPLE SIZE
Tests were conducted to determine the effect of sample size on
adhesion measurements. These test results indicate that a minimum cross
sectional area of 2 in. x 2 in. (5.1 cm x 5.1 cm) is necessary to avoid
reductions in the adhesive strength created by the shrinkage of the shot
crete layer.
These shrinkage effects can be minimized if the samples are kept
intact during curing and if they are prepared immediately prior to testing.
Vibration caused by the saw can also disturb the shotcrete-slab bond contact
and can diminish the adhesive strength. The disturbance created by the saw
can be reduced by precutting the surface slab, binding the cut pieces to
gether and spraying shotcrete on the slab mosaic. The samples are prepared
by sawing the shotcrete along the precut sides of the slab sections. This
technique works very well for obtaining samples with young shotcrete or
having poor shotcrete-slab bond. The adhesive strength values shown in
Tables C-1 to C-4 are probably lower than the actual adhesion developed in
the model.
* U . S. GOV ER NMENT PRINTING OF FICE: 1976 - 21 1 · 173/486
C-11
-
, . ,• I