ND-A172 365 CENTRIFUGAL CONSOLIDATION TESTING OF SOFT SOIL(U) 1/1GIBSON (ROBERT E) FERRING (ENGLAND) R E GIBSON LMDRJR45-B5-N-533

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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDARDS-1963 A

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REPORT DOCUMENTATION PAGE READ INSTRUCTI

I BEFORE COMPLETING FORM

IREPORT NUMBER 2. GOVT ACCESSION No. 3. RECIPIENT'S CATALOG NUMBER

In __________y 014

cc 4. TITLE (mni Subtitle) S. TYPE OF REPORT & PERIOD COVERED

CENTRIFUGAL CONSOLIDATION TESTING OF Final Report a

SOFTSOI 6. PERFORMING ORG. REPORT NUMBER

. 6UHRs . CONTRACT OR GRANT NUMBER(&)

PROF. R.E. GIBSON DAJA45-85-M-0533

__9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASK

LI AREA & WORK UNIT NUMBERS

S 23 SOUTH DRIVE,61102A 1T161102BH57-01

FERRING, WEST SUSSEX BN12 5QU, UK

1I. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

USARDSG-UK 13. NUMBER OF PAGES

BOX 65, FPO NY 09510

14. MONITORING AGENCY NAME & ADDRESS(If diff erent from Controlling Office) IS. SECURITY CLASS. (of this report)

UNCLASSIFIED

ISO. DECLASSIFICATION/DOWNGRADINGSCHEDULE

16. DISTRIBUTION STATEMENT (of this Report)

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, If different from Report)

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

IS 1 SUPPLEMENTARY NOTES E E(T~kAUG 5 1986

S 19. KEY WORDS (Continue on reverse side it necessary mid identify by block number)

CENTRIFUGAL CONSOLIDATION TESTING OF SOFT SOILS, CENTRIFUGE

TESTING r

20 ABSTRACT (Continue on reverse side If necessary and Identify by block number) .'

~SERIES OF CENTRIFUGAL CONSOLIDATION TEST 4 G ON SOFT CLAYS WAS4ERFOMEDTO MODEL THE SELFWEIGHT CONSOLIDATION PROCESS OF A

SOFT CLAY IN WHICH THE DEFORMATION IN THE DIRECTION OF GRAVITY

IS DOMINANT WHILE THE FLOW OF WATER IS FREE TO OCCUR IN BOTH f

VERTICAL AND LATERAL DIRECTIONS. RESULTS OF TEST ING,IN CLUDE D IN

REPORT. 1

DD I J N 7 1473 EDITION OF I NOV 65 IS OBSOLETE rTAqF1)SECURITY CLASSIFICATION OF THIS PAGE (Whesn Date Entered)

% %.

CENTRIFUGAL CONSOLIDATION TESTING OF SOFT SOIL

(being the Final Report to U.S.A.R.D.S.G.-U.K. under

Contract No. DAJA45-85-M-0533 and Requisition R&D 4933-EN-Ol/A)

1. INTRODUCTION .

The objective offhn research vn dertaken is to provide physical

modelling data which will enable the validation of existing theory and/or

will provide data to permit empirical correction factors to existing

theories which will model field geometries. -21 I " j /-

The first Interim Report described a pilot centrifuge model test

(Test #1). The second Interim Report described two additional tests

(Tests #2 and 3) and the data was reported. This Final Report the last

two tests of the series are reported (Tests #4 and 5).

The intention of these series of tests was to model the self-weight

consolidation process of a soft clay in which the deformation in the

direction of gravity is dominant while the flow of water is free to occur

in both vertical and lateral directions.

2. Test #4

Test #4 was conceived as benchmark test in which only one

dimensional (vertical) water flow is allowed. Thus the comparison of the

test results of other tests with the results of this test will provide

information regarding the influence of the lateral draining on the

consolidation process.

2.1 Model Container

The same model container as in the previous tests was used in this

* test. However, there was no lateral porous stone in this test so that

the water drainage was only in the vertical direction.

2.2 Material Characteristics

The same material as in the previous tests was used.

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2.3 Model Preparation and Testing

The model preparation and testing procedure was identical to those

used in the previous tests. This test lasted for 10.5 hours.

2.4 Test Results

The test results showing pore pressures and settlements are

presented in the attached Figures. The changes in pore pressure with

fine at the three pore pressure parts are presented in Figure 1. The

measured values are consistent indicating almost identical dissipation

pattern for all three measuring parts. Since the test was really

one-dimensional such a response was anticipated.The changes with time of the model height are presented in Figures 2

through 8 for scales I through 7. Corresponding settlement are presented

in Figures 9 through 15 using an arithmetic time scale and Figures 16

through 22 using a logarithmic time scale. Figure 26 summarizes the

results of the surface settlements.

A photograph of the model in flight is shown in Figure 23. It shows

uniform settlement of the whole surface.

At the end of the test the material was sampled at five locations in

five layers. The void ratio distribution is presented in Table 1.

Table 1

VOID RATIO DISTRIBUTION AFTER TEST #4A B C D E

1 2.76 2.81 2.58 2.66 2.55

2 2.48 2.46 2.39 2.36 2.36

3 2.34 2.34 2.33 2.26 2.25

4 2.19 2.20 2.22 2.19 2.13

5 2.12 2.12 2.17 2.15 2.11

i DTIC "CELECTEAUG 5 1986 -2-

V e

3. Test #5

Test #5 was designed to provide two additional pieces of information

not available from the previous tests. First, an attempt was made to

obtain a complete deformation picture of soil elements in the vicinity of

the drained lateral boundary and second to obtain pore pressure history

at a point very near the porous drainage plate. The deformation

measurements were to be taken by observing deformations of an embedded

grid consisting of flexible noodles.

3.1 Model Container

The same container as in previous tests was used except for the

position of the porous plate. Schematic drawing is presented in Figure

24 in which the porous plate position is indicated.

3.2 Material Characteristics

The same material as in the previous test was used.

3.3 Model Preparation and Testing

The model preparation and testing procedure was identical to those

used in the previous tests. This test lasted for 9.5 hours.

3.4 Test Results

In this test only data indicating the pore pressure changes wit time

were obtained. There are presented in Figure 25 for all three pore

pressure measuring parts. The camera for taking still photographs was

focused on the area near the porous plate, thus not all the scales were

visible. The vertical and horizontal noodles in this test deformed in a

random fashion and no coherent deformation pattern could be detected. A

photograph showing the noodles' position in flight is shown in Figure 26.

After the test the material was sampled at five locations in five

layers. The void ratio distribution is presented in Table 2.

°*%

Table 2

VOID-RATIO DISTRIBUTION AFTER TEST #5

A B C D E

1 2.58 2.61 2.82 2.72 2.50

2 2.40 2.45 2.54 2.46 2.34

3 2.27 2.32 2.42 2.34 2.26

4 2.23 2.25 2.29 2.25 2.20

4 5 2.20 2.22 2.25 2.15 2.15

4. CONCLUSIONS

The executed testing program provides sufficient information to make

the following conclusions:

1) The centrifuge modeling technique proved to be a powerful tool forstudying the influence of lateral drainage on the consolidation process

of soft material. d

2) The pore pressures dissipated faster in the vicinity of the lateral

porous plate. The combined pore pressure dissipation data from tests 2, IN

3, 4 and 5 provide a complete picture of the pore pressure distribution

at the bottom of the consolidating layer.

. 3) The influence of the lateral drainage on the pore pressure diminishes

at a distance of approximately 4" for the model tested which corresponds

to 1.3 times the initial height of the consolidating layer.

4) Settlements progress faster in the vicinity of the lateral drainage

plate but the ultimate settlements are the same indicating that no

significant side friction developed.

5) Though the external lateral deformations were prevented with the

rigid porous plate the internal deformations in the horizontal direction

were significant in the vicinity of the vertical drained boundary.

-4-

a.,"

6) Only a nnerical analysis of the perfored tests could anser the

question about the importance of the observed lateral deformations.

,.. Their influence on the overall consolidation process could also be

*" evaluated in the case that a complete analysis is performed.

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