reinforced soil walls-6 · (()kn/m) 1 12.5 kpa frictional with lap length of 1.3m 20.6...
TRANSCRIPT
Geosynthetics and Reinforced Soil Structures
Testing Requirements Testing Requirements for Design of Reinforced
Soil WallsSoil Walls
Prof K. RajagopalDepartment of Civil Engineeringp g g
IIT Madras, Chennaie mail: gopalkr@iitm ac ine-mail: [email protected]
Tests Required for the Design of R i f d S il R t i i W llReinforced Soil Retaining Walls
• Properties of soil• Properties of soil• Properties of reinforcement• Soil-reinforcement interaction factors• Reinforcement facing connection• Reinforcement-facing connection
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SHEAR STRENGTH SHEAR STRENGTH PROPERTIES OF SOIL
• C=0 (cohesive strength is neglected)• Friction angle determined from small or large-box
shear tests (stress state in direct shear box similar to that behind retaining wall)R f l i th t t h ld• Range of normal pressures in the tests should correspond to those expected in reinforced soil fill
• Peak friction angle is used for designsPeak friction angle is used for designs
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Longterm Allowable Design Strength
CRF TT ultLTDS
Tult from index tension tests (ASTM D6637 or ASTM D4595)
FSFBFDFCT LTDS
ult ( )
FC is the environmental degradation factor
FB is the biological degradation factor
FD is the construction induced damage (depends on method of compaction, size of aggregate etc.)
FS i ll f t f f tFS is overall factor of safety
CRF = creep reduction factor (depends on type of polymer, duration of service life, temperature, etc.)
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Immersion of geosynthetic samples in a chemical environment to study the chemical/environmental degradation factor
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Source: IGS
Reference Geosynthetic Tensile TestsReference Geosynthetic Tensile Tests
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Courtesy: Prof R.J. Bathurst, Royal
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Military College of Canada
Wide‐width strip tensile test resultsD 4595 ‐ 86
Specimen gauge length = 200 mm
Tult = ultimate tensile strength
Rate of displacement equivalent to 10% strain/min
Courtesy: Prof R.J. Bathurst, Royal
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Military College of Canada
Long‐Term Design StrengthLong Term Design Strength
FS = 1.25 to 1.5 (typical)
To take care of uncertainties in quality of the material and manufacturing defects etcmaterial and manufacturing defects, etc.
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Default Values for Partial Factors of SafetyDefault Values for Partial Factors of Safety
Guidelines for Design, Specification, and Contracting of Geosynthetic Mechanically Stabilized Earth Slopes on Firm Foundations, Berg 1993
partial factorpartial factor
installation damage 3.0
creep 5.0p
chemical degradation 2.0
biological damage 1.3
joint/seam 2.0
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TTa
Tultult
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Determination of partial factor for creep
f l hFSCR = ratio of Tult to creep‐limiting strength
Constant load creep testing
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Determination of FSCRExample from in‐isolation creep rupture of a woven polyester
id
4500
5000
geogrid
Tult
y = ‐93.18Ln(x) + 4210
3500
4000
4500
y = ‐89.462Ln(x) + 4104.8
2000
2500
3000
oad(lb
/ft) T75 years
FS = T
1000
1500
2000
lo FSCR = TultT75 years
0
500
0.0001 0.001 0.01 0.1 1 10 100 1000 10000 100000
l d ti (h )1000000
FSCR = 1.67
114 yearselapsed time (hrs)
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Courtesy: Prof R.J. Bathurst, Royal Military College of Canada
1.20
1.00
CREEP CURVES SS20 : 5 bars x 6 ribs
8.1 kN/m
0.60
0.80
rain
(%)
___ experimentpredicted (TRF)
0.40
str - - - predicted (TRF)
6.0 kN/m
0.00
0.20
4.3 kN/m
6.0 kN/m
Creep testing of geosynthetics
Typical creep test data of geosynthetics
0 2000 4000 6000time (hours)
Creep testing of geosynthetics
00 5 10 15 20 25
Strain%
-1
-3
-2
/mm
)
43 1 (kN/m)
5
-4
n ra
te(%
stra
in/ 43.1 (kN/m)
40.2
-6
-5
Stra
in
T 80 kN/
-8
-77.1 28.514.3
Sherby Dorn plot between strain rate and strain
Tindex = 80 kN/m
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8 Sherby-Dorn plot between strain rate and strain
Standard Test Method for Accelerated Tensile Creep and Creep-Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped Isothermal MethodMethod
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TU-40 geogrid at 68% load level in SIM test
8.6
8.5
8.4
stra
in (
%)
8.3
8.20 2000 4000 6000 8000 10000 12000
time (seconds)
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time (seconds)
room temperature Temp = 45 deg. Temp = 59 deg. Temp = 73 deg. Temp = 87 deg. Temp = 95 deg.
Installation damageInstallation damage
ASTM D 5818‐95 ASTM 4595‐86 and FederalASTM D 5818 95, ASTM 4595 86 and Federal Highway Administration guidelines (Publication No FHWA NHI‐00‐044 dated March 2001)No. FHWA NHI 00 044 dated March 2001).
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90
100
Project‐specific aggregate
50
60
70
80
Pass
ing
10
20
30
40
%
Place steel plates00.01 0.1 1 10 100 1000
Particle Size (mm)
Place steel plates
Place aggregate base layer Place geosynthetic samples
21Reinforced Soil Walls ‐ 6
Place cover aggregateCompact aggregate using project‐specific compaction equipmentPlace cover aggregate specific compaction equipment
Exhume samples22Reinforced Soil Walls ‐ 6
Publication No. FHWA NHI‐00‐044Publication No. FHWA NHI 00 044
A total of 6 control (virgin) specimens are testedA total of 6 control (virgin) specimens are tested (e.g ASTM 4595‐86).
A minimum of 9 exhumed specimens are required to be tested.required to be tested.
A maximum of 18 tests is required if theA maximum of 18 tests is required if the coefficient of variation from the first 9 tests is greater than 5%.greater than 5%.
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CONTROL: Specimen Peak Load Peak Load
No. (N) (kN/m) 1 19752 109 7
EXHUMED: <150 mm crushed stone Specimen Peak Load Peak Load
No. (N) (kN/m) 1 17813 99 01 19752 109.7
2 20884 116.0 3 18839 104.7 4 18972 105.4 5 20067 111.5 6 19243 106 9
1 17813 99.02 17776 98.8 3 17078 94.9 4 17040 94.7 5 16922 94.0 6 18738 104 16 19243 106.9
Mean 19626 109.0 Std. Dev. 773
Coef. of Var. 3.94
6 18738 104.17 18823 104.6 8 17030 94.6 9 18217 101.2
Mean 17715 98.4 Std Dev 750Std. Dev. 750
Coef. of Var. 4.23
RFID = 109.0/98.4 = 1.11
Courtesy: Prof R J Bathurst RMC
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Courtesy: Prof R.J.Bathurst,RMC
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Courtesy: Prof R.J. Bathurst, RMC
Standard Test Method for Determining Connection Strength Between Geosynthetic Reinforcement andStrength Between Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks)
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hydraulic jack to apply l di f
y j pp yvertical load on bricks
loading frame
jack to pull geogrid
geogrid
load cell
blocks
geogrid
a. sectional view of apparatus
load cellload cell
roller grip
b. plan view
L b t t t f ilit f ll t/ ti t t
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Laboratory test facility for pullout/connection tests
Connection test between modular blocks and a uniaxial geogrid
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Openings filled with stone aggregate – drainage blanket
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Close-up of the test arrangement for connection strength tests – LVDT in the picture
Connection loads at serviceability limit of 20 mm
80
90
50
60
70
kN/m
)
30
40
50
pullo
ut lo
ad (k
10
20
p
00 20 40 60 80 100 120
normal load (kN/m)
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GX-40 GX-80 GX-100 GX-130
Ultimate limit state connection load capacity
90
100
60
70
80
/m)
40
50
60
lout
load
(kN
/
10
20
30pul
0
10
0 20 40 60 80 100 120normal load (kN/m)
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normal load (kN/m)
GX-40 GX-80 GX-100 GX-130
Connection strength test between geogrid and facing panel through positive connection – 8 mm HYSD hooks and 16 mm diameter
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pHYSD cross-bar
Arrangement at the front end ith load cell and roller connection
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Arrangement at the front end with load cell and roller connection
geogrid
Normal pressurefacing panel
lsand fill loop
connector rod
sand fill
Schematic of the connection capacity test – rigid p y gconnection at both ends
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Normal pressurei l
geogrid
pfacing panel
loop
connector rod
sand fill
connector rod
Schematic of test set up to determine the strength due to overlap
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Data from connection tests on a geogrid withData from connection tests on a geogrid with Tindex=60 kN/m
Sl. No. Normal pressure Connection type Maximum connection capacity & mode of failure (kN/m)( )
1 12.5 kPa Frictional with lap length of 1.3m 20.6 (pullout/partial rupture)
2 24.5 kPa Frictional with lap length of 1.3m 31 (pullout/partial rupture)p )
3 75 kPa Frictional with lap length of 1.3m 54 kN/m (rupture) 4 75 kPa Clamped connection at both ends 55 kN/m (rupture)
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Connection tests on geogrid with Tindex=350 kN/m
Sl N N l C i M i i
Connection tests on geogrid with Tindex 350 kN/m
Sl. No. Normal pressure
Connection type Maximum connection capacity & mode of failure (kN/m)
1 54.5 kPa Frictional connection (300 mm wide l 1 3 l l th)
148.9 kN/m ( ll t/ ti l t )sample, 1.3 m lap length) (pullout/partial rupture)
2 75 kPa Frictional connection (300 mm wide sample, 1.3 m lap length)
212.4 kN/m (pullout/partial rupture)
3 75 kPa Both ends clamped (300 mm wide l )
322 kN/m (rupture) sample)
4 103.5 kPa Clamped at both ends (300 mm wide sample)
325 kN/m (rupture)
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Standard Test Method for Measuring Geosynthetic Pullout Resistance in SoilGeosynthetic Pullout Resistance in Soil
• Minimum embedment length of sample = 610 mmMinimum embedment length of sample 610 mm• Minimum Length/width ratio = 2• Minimum depth of soil above and below the
reinforcement = 150 mmreinforcement = 150 mm• Rate of pullout displacement = 1 mm per minute
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Interpretation of data from pullout tests on geogrids
P
resistance forcestests on geogrids
P
Le=anchorage length=1.5 m tan2 BLP ev
Sl. No.
Vertical pressure
Peak pullout
Interface friction
=tan/tan
(kPa) load (kN)
angle
1 10.75 kPa 25.9 46.9 >1 1.0 2 3 4
21.6 kPa39.7 kPa 75.9 kPa
41.576.5 127.8
40.5 40.6 36.8
0.92 0.92 0.81
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Testing of Vertical Plate Anchors
Materials – Anchor ReinforcementsStrip
Angles Bolts
Plan
Anchor Strip Size (mm) Angle Size (mm)
Side View Plan
Type
Type I 40 (width) x 5 (thick) and 1500 (length)
50 x 50 x 5 (thick) and 150 (length)
Type II 70 (width) x 5 (thick) and 1500 (length)
130 x 130 x 12 (thick) and 350 (length)
Top view of the steel strip and anchor at endTop view of the steel strip and anchor at end
steel strip
Test series
• Tests were first performed on steel strip alone
• Tests on steel strip and anchors were performed at different normal pressures
• Pullout load applied until about 100 kN maximum load or until peak load
• Measured data includes: Load, front and rear displacements and strains developed in the steel strip
Pullout behaviour of steel strip alonep
8
4
6
forc
e, k
N
2
4
pullo
ut f
length of embedment in soil = 1.2 mDepth of embedment = 0 4 m
070 mm wide strip under 100 kPa pressure
Depth of embedment = 0.4 m
0 20 40 60displacement, mm
Displacement Vs Pullout Force relationship for Type I Anchors
80Pullout Vs Normal Pressure
(Type I Anchors)
60
(Type I Anchors)
12 kPa
25 kPa
50 kPa
100 kPa
40
t For
ce, k
N
150 kPa
20
Pullo
ut
0
0 20 40 60 80Displacement, mm
0
Pullout behaviour of Type 2 anchors
120
100
60
80
ut F
orce
, kN
40Pullo
u
Pullout Force Vs Normal Pressure (Type II (large) Anchors)
12 kPa
25 kPa
0
20 25 kPa
50 kPa
100 kPa
0 20 40 60 80Displacement, mm
BS 8006-1995 formula for pullout capacity of anchored reinforcement elementsreinforcement elements
vaapevsasu tBKLBPPP 42
Ps = skin friction force
Pa = passive capacity due to anchora p p y
v=normal pressure
Bs = width of strip
Le = embedment length of steep strip
Ba, ta = width and height of anchor
K = passive pressure coefficientKp = passive pressure coefficient
Pullout factor for plain steel strip at 100 kPa pressue
Pullout displacement (mm)
Load (kN) Pullout factor
20 6 3 0 382040
6.37.1
0.380.42
Pullout factor is higher at lower normal pressures
Comparison of results with Type-I anchors with BS 8006 formula and others
60Comparison Type I Anchors
formula and others
40NExperimental 20 mm
Experimental 40 mm
BS 8006
Das B M40
ut F
orce
, kN
20Pullo
u
0
0 50 100 150Normal Stress, kPa
Comparison of results with Type-II anchors with BS 8006 formula and othersformula and others
60.00 BS 8006:1995
Experimental Values (40 mm displacement)
Experimental Values (20 mm displacement)
Neely's method (Das B M 1990)
40.00
ut F
orce
, kN
20.00Pullo
u
0.00 25.00 50.00 75.00 100.00
0.00
Normal Stress, kPa
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Steel mesh with a concrete block anchorSteel mesh with a concrete block anchor
Pullout tests on welded mesh with d ffdifferent connections
Working load
Limiting displacement
Connection Capacity
Working load (kN)
Limiting displacement ( )
Connection Capacity (kN) load
(kN) displacement (mm)
Capacity (kN)
40.00 20.00 40.5
(kN) (mm) (kN)40.00 20.00 28.8 40.00 20.00 21.0
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Typical connection failures observed in laboratory tests