Geosynthetic Reinforced Foundations “Laboratory … · Geosynthetic Reinforced Foundations “Laboratory Model Tests & FE Analyses” ... Bridge Deck Slab Pavement Emb Settlement

Geosynthetic Reinforced Foundations “Laboratory Model Tests & FE Analyses”

byMurad Abu-Farsakh, Ph. D., P.E.,

Qiming Chen, and Jie Gu

Louisiana Transportation Research Center

February 12, 2007

AcknowledgmentThe project is financially supported by the Louisiana Transportation Research Center and Louisiana Department of Transportation and Development (LA DOTD).

LTRC Project No. 04-2GT .

Bridge Deck Rigid Slab Pavement

Footing

Pile Group

δ

Problem StatementBridge Bump Problem

Uncomfortable rides Dangerous driving conditions Costly frequent repairs

Bridge Deck Slab Pavement

Emb Settlement

Pile Group

Bump 2

Bump 1

Bump 1

Bump 2

δB

δD

δ

θ

δs

Problem StatementReinforced Soil Foundation (RSF)

Reinforcing embankment soil directly Replacing the soils with stronger granular fill in combination with the inclusion of geosynthetics

ObjectivesInvestigate the influences of different variables and parameters contributing to the benefits of RSF,

Study the stress distribution within the soil mass for unreinforced and reinforcement conditions, and the strain distribution along the reinforcement,

Examine the existing analytical methods and/or develop new analytical/FE methods.

Design Parameters of RSF

Effective length of reinforcement (LR), Depth to top (first) reinforcement layer (u),Effective reinforcement depth (d),Number/Spacing of reinforcement layers,Type and stiffness of reinforcements,Soil-reinforcement interaction,Footing’s embedment depth.

Typical Geosynthetic RSFTypical geosynthetic RSF with the geometric parameters and a typical layout of instrumentation

BClay

Strain Gauges

Footing

h

h

u

d

h

h

203 mm203 mm203 mm

203 mm203 mm203 mml

N=3

N=2

N=1

N=5

N=4

d: Total depth of reinforcementh: Vertical spacing between layersu: Top layer spacingB: W idth of footing

N: Number of reinforcement layersPressure Cells

: Length of reinforcement

Dial gaugeLoad Cell

Geosynthetic

Research Approach

Small-Scale Lab Model TestEmbankment silty clay soilCrushed limestone Sand soil

Large-Scale Field Model TestEmbankment silty clay soil

Finite Element AnalysisEmbankment soilCrushed Limestone

Material Properties

Soils

Soil Type Dry Density (kg/m3)

Moisture Content (%)

Friction Angle (φ)

Embankment Soil

1670 18 25o – 30o

Crushed Limestone

2268 7.5 48o-53º

Sand 1620 4.8 40o-45o

Material PropertiesReinforcement

Reinforcement Polymer TypeTa, kN/m Eb, kN/m Aperture

Size, mmMDc CDd MDc CDd

GG1 geogrid Polyester 7.3 7.3 365 365 25.4×25.4GG2 geogrid Polypropylene 3.6 5.1 182 255 33×33GG3 geogrid Polypropylene 5.5 7.4 274 372 33×33GG4 geogrid Polypropylene 4.1 6.6 205 330 25×30.5GG5 geogrid Polypropylene 6.0 9.0 300 450 25×33GG6 geogrid Polypropylene 8.5 10.0 425 500 25×30.5GG7 geogrid Polypropylene 6.1 9.0 305 450 25×30.5

GT1 geotextile Polypropylene 14 19.3 700 965 ≈ 0Steel Wire Mesh Stainless Steel 236 447 11780 22360 25×51Steel Bar Mesh Steel 970 970 48480 48480 76×76

Lab Testing ProgramTests were conducted in a steel box with dimensions of 5 ft (length) × 3 ft (width) × 3 ft (height),The model footing: a steel plate with dimensions of 6 in × 6 in (B×L) ×1 in thick,Sample preparation: The soil was compacted in lifts. The lift thickness depends on the number and location of reinforcement,Compaction: three passes: 8 seconds (1st pass) → 3 seconds (2nd pass)→ 1 second (3rd pass) of vibratory jack hammer.Quality Control: Geogauge & Nuclear Density Gauge.

A Complete Test Set-up

Multiplexer

Data Logger

Load CellDial Gauge

Computer

Hydraulic Jack

Reaction Frame

Reference Beam

Lab Testing Program

Lab Testing ProgramPressure Cell

Geosynthetic

BSoil

203 mm203 mm203 mm

203 mm203 mm203 mm

Pressure Cells

102 mm

51 mm

102 mm

FootingPressure Cell

Model: Geokon Model 4800 Model: Geokon Model 4800 VW earth pressure cellsVW earth pressure cells

Diameter: 4 in.Diameter: 4 in.

Lab Testing ProgramStrain Gages

Geosynthetic

BSoil

51 mm

51 mm

51 mm

51 mm

Strain Gages

Footing

Resistance: 120±0.15%Ω

Gage Factor: 2.055±0.5%

Evaluation of ParametersThe benefits of RSF were evaluated in terms of :

Bearing Capacity Ratio (BCR) : the ratio of the bearing capacity of the reinforced soil to that of the unreinforced at a specific settlement.

Settlement Reduction Factor (SRF) : the ratio of the settlement of the reinforced soil to that of the unreinforced at a specific surface pressure.

Improvement in Vertical Stress Distribution :below reinforced zone.

Evaluation Parameters

qR, q: bearing capacity of reinforced soil and unreinforced soil at a settlement of ssR, s: settlement of reinforced soil and unreinforced soil at a surface pressure of q

s

q Rq

sR

Applied Pressure

Foot

ing

Settl

emen

t

qRq

BCR =

SRF =s Rs

Unreinforced ReinforcedSoil Soil

Test Factorial - Silty Clay

Footing Reinforcement Df/B Variable Parameter Constant Parameters

6 in × 6 in

No 0 NA NA

GG1 0u = 1, 2, 3, 4, 5, 6, 8 in. N=1

N = 1, 2, 3, 4, 5 u = 2 in., h = 2in

GG2 0 N = 1, 2, 3, 4, 5 u = 2 in., h = 2in

GG3 0N = 1, 2, 3, 4, 5 u = 2 in., h = 2in

h = 1, 2, 3, 4 in. u = 2 in., N = 3

GT1 0 N = 1, 2, 3, 4, 5 u = 2 in., h = 2in

Test Results and Analysis-Silty ClayTop Layer Spacing (u) – GG1 geogrid

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 200 400 600 800 1000 1200

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

)

NR ...GG1 25GG1 51GG1 76GG1 102GG1 127GG1 152GG1 203

Type u (mm)

(u/B)opt ≈ 0.330.33

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

u/B

BC

R

s/B=3%s/B=10%s/B=16%

Test Results and Analysis-Silty ClayInfluence Depth (d) – GG1 geogrid

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

) NR 0GG1 1GG1 2GG1 3GG1 4GG1 5

Type N

(d/B)cr ≈ 1.51.5

1.0

1.2

1.4

1.6

1.8

2.0

0 1 2 3 4 5

N

BC

R0.00 0.33 0.67 1.00 1.33 1.67

d/B

s/B=3%s/B=10%s/B=16%

Test Results and Analysis-Silty ClayInfluence Depth (d) – GG3 geogrid

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

) NR 0GG3 1GG3 2GG3 3GG3 4GG3 5

Type N

(d/B)cr ≈ 1.51.5

1.0

1.2

1.4

1.6

1.8

2.0

0 1 2 3 4 5

N

BCR

0.00 0.33 0.67 1.00 1.33 1.67d/B

s/B=3%s/B=10%s/B=16%

Test Results and Analysis-Silty ClayVertical Spacing (h) – GG3 geogrid

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 200 400 600 800 1000 1200 1400 1600 1800

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

)

NR ... ...GG3 51 25GG3 51 51GG3 51 76GG3 51 102

Type u h (mm)(mm)

h/Bh/B BCRBCR

1.00

1.20

1.40

1.60

1.80

0.00 0.20 0.40 0.60 0.80

h/B

BC

R

s/B=3%s/B=10%s/B=16%

Test Results and Analysis-ClaySettlement Reduction Factor

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400 500 600 700 800

q (kPa)

GG2 1 51GG2 2 51GG2 3 51GG2 4 51GG2 5 51

Type N u(h) (mm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400 500 600 700 800

q (kPa)

SRF

GT1 1 51GT1 2 51GT1 3 51GT1 4 51GT1 5 51

Type N u(h) (mm)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400 500 600 700 800

q (kPa)

GG3 1 51GG3 2 51GG3 3 51GG3 4 51GG3 5 51

Type N u(h) (mm)

0.00.20.40.60.8

1.01.21.41.6

0 100 200 300 400 500 600 700 800

q (kPa)

SRF

GG1 1 51GG1 2 51GG1 3 51GG1 4 51GG1 5 51

Type N u(h) (mm)

-2

0

2

4

6

8

10

12

-5 -4 -3 -2 -1 0 1 2 3 4 5

Relative Distance From the Center of Footing (x/B)

Stre

ss (k

Pa)

UNR 0 0 0GG2 51 51 5GG3 51 51 5GG1 51 51 5GT1 51 51 5

Type u h N (mm) (mm)

69% reduction

18% reduction

Stress Distribution-Silty Clay

Surface pressure, q=47 kPa

-30

0

30

60

90

120

150

-5 -4 -3 -2 -1 0 1 2 3 4 5

Relative Distance From the Center of Footing (x/B)

Stre

ss (k

Pa)

UNR 0 0 0GG2 51 51 5GG3 51 51 5GG1 51 51 5GT1 51 51 5

Type u h N (mm) (mm) 18% reduction

36% reduction

Surface pressure,q=468 kPa

Strain Along the Reinforcement-Silty Clay

-0.5

0.0

0.5

1.0

1.5

2.0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Relative Distance From the Center of Footing (x/B)

Stra

in (%

)

1%2%3%4%5%6%8%10%12%14%16%

s/B

strain gauge broken

(l/B)cr ≈ 5.0-0.5

0.0

0.5

1.0

1.5

2.0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Relative Distance From the Center of Footing (x/B)

Stra

in (%

)

1%2%3%4%5%6%8%10%12%14%16%

s/B

At a depth of 1/3B

At a depth of 5/3B

Finite Element Analysis

00.5

11.5

22.5

33.5

44.5

5

0 100 200 300 400 500 600 700 800 900 1000

Footing Pressure (psi)

Foot

ing

Sett

lem

ent (

inch

) 0

20

40

60

80

100

120

0 1000 2000 3000 4000 5000 6000

(kPa)

(mm

)

3 layer reinforced soil4 layer reinforced soil6 layer reinforced soil8 layer reinforced soil12 layer reinforced soil

Typical pressure-settlement Curve (Type III geogrid)

Finite Element Model

Finite Element - Results

Optimum depth of first reinforced layer

0.00.20.40.60.81.01.21.41.61.82.0

0.0 0.2 0.4 0.6 0.8 1.0

Depth ratio (u/B)

Bea

ring

Cap

acity

Rat

i

Three-layer reinforced soil

Two-layer reinforced soil

One-layer reinforced soil

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 1 2 3 4 5 6 7 8 9 10

Number of Geogrid Layers

BC

R a

t s/B

=10%

0 0.5 1 1.5 2 2.5Reinforcing Depth Ratio, D/B

Type VIII GeogridType VI GeogridType III Geogrid

Influence depthof reinforced zone

Finite Element - Results

Effect of reinforcement Stiffness

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.5 1 1.5 2 2.5 3 3.5 4

Normalized Geogrid Stiffness

Settl

emen

t Rat

io, s

/B

3-layer reinforced soil4-layer reinforced soil6-layer reinforced soil8-layer reinforced soil12 layer reinforced soil

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

0 0.5 1 1.5 2 2.5 3 3.5 4

Normalized Geogrid Stiffness

Bea

ring

Cap

acity

Rat

io a

t s/B

=10%

3-layer reinforced soil4-layer reinforced soil6-layer reinforced soil8-layer-reinforced soil12-layer reinforced soil

Finite Element – Regression Model

BCR = 1.7761- 2.0237*X1 + 0.12367*X2 + 0.56264*X3 - 0.01889*X4 - 0.08193*X5

(R2=0.98)

Where: BCR: bearing capacity ratio of the reinforced soil (at s/B=10),X1: is the spacing ratio between geogrid layers (h/B),X2: is the stiffness ratio of reinforcement included in the reinforced soil

(i.e. Ereinforcement/Esoil),X3: is the interaction coefficient between reinforcement layers and soil,X4: is the footing embedment ratio (D/B), X5: is the footing width ratio (B/4ft).

Verification of BCR Regression Model

h (in) X1

Egeogrid

(psi) X2 CI

* X3Df

(in) X4

B (in) X5

BCR (Fem)

BCR (Reg)

Abs (Err) (%)

12 0.25 43850 1.16 0.5 0.5 0.0 0.00 4.0 1.0 1.62 1.61 0.16 12 0.25 43850 1.16 0.7 0.7 0.0 0.00 4.0 1.0 1.69 1.73 2.13 12 0.25 91280 2.42 0.5 0.5 0.0 0.00 4.0 1.0 1.78 1.77 0.48 12 0.25 131800 3.50 0.7 0.7 0.0 0.00 4.0 1.0 1.99 2.01 1.01 24 0.50 54620 1.45 0.7 0.7 0.0 0.00 4.0 1.0 1.32 1.26 4.79 24 0.50 102100 2.71 0.7 0.7 0.0 0.00 4.0 1.0 1.45 1.41 2.98 12 0.25 102100 2.71 0.7 0.7 0.0 0.00 4.0 1.0 1.84 1.92 4.22 6 0.13 54620 1.45 0.7 0.7 0.0 0.00 4.0 1.0 2.05 2.01 1.62 6 0.13 102100 2.71 0.7 0.7 0.0 0.00 4.0 1.0 2.23 2.17 2.63 18 0.38 43850 1.16 0.7 0.7 0.0 0.00 4.0 1.0 1.50 1.47 1.80

Developed Plastic Zones

In unreinforced soil In 3-layers geogrid reinforced soil

Test Factorial-Crushed Limestone

Footing Reinforcement Df/B Variable Parameter Constant Parameters

6 in × 6 in

No 0 NA NA

GG1 0 N = 1, 2, 3 u = 2 in., h = 2in

GG4 0 N = 1, 2, 3 u = 2 in., h = 2in

GG5 0 N = 1, 2, 3 u = 2 in., h = 2in

GG6 0 N = 1, 2, 3 u = 2 in., h = 2in

GG7 0 N = 1, 2, 3 u = 2 in., h = 2in

SWM 0 N = 1, 2, 3 u = 2 in., h = 2in

SBM 0 N = 1, 2, 3 u = 2 in., h = 2in

Test Results and Analysis-Crushed Limestone

Type and Stiffness of Reinforcement-One Layer

0.00

0.04

0.08

0.12

0.16

0.20

0.24

0.28

0 2000 4000 6000 8000 10000 12000

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

)

Unreinforced ... ...GG4 1 51GG1 1 51GG5 1 51GG7 1 51GG6 1 51SWM 1 51SBM 1 51

Type N u (mm)

Stiffness Stiffness increaseincrease

0.0

0.5

1.0

1.5

2.0

2.5

GG4 GG1 GG5 GG7 GG6 SWM SBM

Stiffness

BC

R

1 51 ...2 51 513 51 51

N u h (mm)(mm)

Test Results and Analysis-Crushed LimestoneNumber of Layers and Stiffness of Reinforcement

StiffnessStiffness BCRBCR0.0

0.5

1.0

1.5

2.0

2.5

3.0

GG4 GG1 GG5 GG7 GG6 SWM SBM

Stiffness

BC

R

1 51 ...2 51 513 51 51

N u h (mm)(mm)

s/B=3%

s/B=10%

0.0

0.2

0.4

0.6

0.8

1.0

0 1000 2000 3000 4000 5000 6000

q (kPa)

SRF

GG4 3 51 51GG1 3 51 51GG5 3 51 51GG7 3 51 51GG6 3 51 51SWM 3 51 51SBM 3 51 51

Type N u h (mm)(mm)

Test Results and Analysis-Crushed LimestoneSettlement Reduction

0.0

0.2

0.4

0.6

0.8

1.0

0 1000 2000 3000 4000 5000 6000

q(kPa)

SRF

GG4 2 51 51GG1 2 51 51GG5 2 51 51GG7 2 51 51GG6 2 51 51SWM 2 51 51SBM 2 51 51

Type N u h (mm)(mm)

0.0

0.2

0.4

0.6

0.8

1.0

0 1000 2000 3000 4000 5000 6000

q(kPa)

SRF

GG4 1 51GG1 1 51GG5 1 51GG7 1 51GG6 1 51SWM 1 51SBM 1 51

Type N u (mm)

Finite Element - Results

Optimum depth of first reinforced layer

Typical pressure-settlement curve

0

0.05

0.1

0.15

0.2

0.25

0 500 1000 1500 2000

Footing Pressure (psi)

Foot

ing

Settl

emen

t (B

)

0 1000 2000 3000 4000 5000 6000 7000 8000Footing Pressure (kPa)

unreinforced soil3-layer reinforced soil4-layer reinforced soil6-layer reinforced soil12-layer reinforced soil

11.051.1

1.151.2

1.251.3

1.351.4

1.451.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Top Layer Spacing (B)

BC

R

1-layer reinforced soil2-layer reinforced soil3-layer reinforced soil

Finite Element - Results

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

0 1 2 3 4 5 6

Normalized Stiffness

BC

R a

t s/B

=10%

12-layer reinforced soil6-layer reinforced soil3-layer reinforced soil

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6

Normalized Stiffness

SR

F at

Fin

al S

tate

of

Unr

einf

orce

d S

oil

12-layer reinforced soil6-layer reinforced soil3-layer reinforced soil

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8

Distance from Central Axis along the horizontal line 1.5 B below footing (B)

Vert

ical

Stre

ss D

evel

oped

at f

inal

sta

te

of u

nrei

nfor

ced

soil

(psi

)

0

500

1000

1500

2000

2500

3000

3500

4000(k

Pa)unreinforced

3-layer SW reinforced soil6-layer SW reinforced soilunre asso

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8

Distance from Central Axis along the horizontal line 1.5 B below footing (B)

Vert

ical

Stre

ss D

evel

oped

at f

inal

sta

te

of u

nrei

nfor

ced

soil

(psi

)

0

500

1000

1500

2000

2500

3000

3500

4000

(kP

a)unreinforced3-layer SW reinforced soil6-layer SW reinforced soilunre asso

Finite Element – Regression Model

BCR = 1.84917-0.29706*X1 + 0.03031*X2 -0.2015*X3 - 0.34724*X4

(R2=0.98)

Where: BCR: is the ultimate bearing capacity ratio of the reinforced soil (at

s/B=10),X1: is the spacing ratio between geogrid layers (h/B),X2: is the normalized stiffness of reinforcement included in the

reinforced soil ,X3: is the footing embedment ratio (D/B), X4: is the footing width ratio (B/4ft).

Verification of BCR Regression Model

No.X1 X2 X3 X4 BCR

(Fem)BCR

(Reg)Abs (Err)

(%)

1 0.375 0.4 0.0 1.0 1.69 1.73 2.13

2 0.375 1.77 0.0 1.0 1.99 2.01 1.01

3 0.375 0.59 0.5 1.0 1.84 1.92 4.22

4 0.375 0.59 1.0 1.0 2.23 2.17 2.63

5 0.375 0.59 0.0 0.75 1.50 1.47 1.80

6 0.375 0.59 0.0 1.5 1.63 1.63 0.20

7 0.1875 0.80 0.0 1.0 1.47 1.47 0.23

8 0.1875 3.54 0.0 1.0 1.56 1.55 0.22

9 0.1875 1.18 0.5 1.0 1.37 1.38 0.52

10 0.1875 1.18 1.0 1.0 1.28 1.28 0.09

11 0.1875 1.18 0.0 0.75 1.62 1.57 3.27

12 0.1875 1.18 0.0 1.5 1.32 1.31 0.99

Large-Scale Testing ProgramTest dimensions: 3.658 m (12 ft) (length) × 3.658 m (12 ft) (width) × 1.829 m (6 ft) (height),The model footing: a concrete block with dimensions of 452 mm (1.5 ft) × 452 mm (1.5 ft) (B×L) ×254 mm thick,Section preparation: a tiller was used to mix the cohesive soil and water. The soil was compacted in lifts. The lift thickness depends on the number and location of reinforcement,Compaction: MultiQuip Plate Compactor → three passes

Wacker-packer → six passes

Test Factorial

Reinforcement Type

No. of Reinforcement

Layers

umm

h mm

Unreinforced* - … ...

GG2 4 152 203

GG3 3 152 305

GG3 4 152 203

GG3 5 152 152

GG4 4 152 203

Test Results and Analysis

0.00

0.05

0.10

0.15

0.20

0.25

0 500 1000 1500 2000

Applied Pressure ( kPa)

Sett

lem

ent R

atio

(s/B

)

Unreinforced ... ... ...GG2 152 203 4GG3 152 305 3GG3 152 203 4GG3 152 152 5GG4 152 203 4

Type u h N (mm) (mm)

1.0

1.1

1.2

1.3

1.4

1.5

GG2 GG3 GG4

Stiffness

BC

R

s/B=3%s/B=5%s/B=8%

N= 4, u= 152 mm, h= 203 mm

1.0

1.1

1.2

1.3

1.4

1.5

s/B=3% s/B=5% s/B=8%

BC

R

3 152 3054 152 2035 152 152

N u h (mm) (mm)

Analytical Solution – Silty ClayThe following failure mode would occur in reinforced soil foundation (Wayne, et al., 1998)

BFooting

Reinforcementd

qbT

After Deformation

ca ca

ccaa, , φφaa, , γγaa

ccbb, , φφbb, , γγbb

dBLTLB

BLLBK

dDd

BLdLBcqq a

as

faabult γ

φγ −+++⎥⎦

⎤⎢⎣⎡ ++++= )(2tan)(21)(2 2

Analytical Solution – Silty ClayBased on Meyerhof and Hanna’s solution for two layer soil system, Wayne, et al. (1998) proposed:

dBLTLB

BLLBK

dDd

BLdLBcqq a

as

faabult γ

φγ −+++⎥⎦

⎤⎢⎣⎡ ++++= )(2tan)(21)(2 2

qqbb = ultimate bearing capacity of the foundation below the = ultimate bearing capacity of the foundation below the reinforced zone;reinforced zone;

B = width of the footing; L = length of the footing;B = width of the footing; L = length of the footing;d = total depth of reinforcement; Dd = total depth of reinforcement; Dff = embedment depth of the = embedment depth of the

footing;footing;KKss= punch shear coefficient, which depends on friction angle of= punch shear coefficient, which depends on friction angle of

upper layer soil and the ultimate bearing capacity of botupper layer soil and the ultimate bearing capacity of bothhupper and lower soil layers;upper and lower soil layers;

T = uplift or restraining force of the reinforcements.T = uplift or restraining force of the reinforcements.

Measured Vs. Calculated – Silty Clay

GG1 Geogrid

1.0

1.2

1.4

1.6

1.8

2.0

0 1 2 3 4 5

N

BC

R

Measured, BCR@s/B=10% (GG1)Calculated (Wayne, et al., 1998)Finite Element Analysis

1.0

1.2

1.4

1.6

1.8

2.0

0 1 2 3 4 5

N

BC

RMeasured, BCR@s/B=10% (GG3)Calculated (Wayne, et al., 1998)Finite Element Analysis

GG3 Geogrid

Summary and ConclusionsThe optimum depth of the top reinforcement layer was found to be 0.3B - 0.35B,The bearing capacity increases with increasing the number of reinforcement layers within the influence zone. The influence depth of the reinforced zone was found to be ≈1.5 B,The effective length of reinforcement was found to be ≈5 B, Geogrids with higher stiffness performed better than geogrids with lower stiffness,The bearing capacity increases with the increase in reinforcement stiffness and with the decrease in the vertical spacing of reinforcement layers,

Summary and ConclusionsImmediate settlement can be reduced significantly with soil reinforcement. It decreases with the increase in reinforcement stiffness and with the decrease in reinforcement spacing,The inclusion of reinforcement improves the vertical stresses distribution below the influenced depth. This will be resulted in reducing the soil’s consolidation settlement,Regression models were developed from FE results, and were verified,The analytical solution proposed by Wayne, et al. (1998) and the finite element analysis are in good agreement with the experimental test results.

THANK YOU

Questions