behavior of reinforced embankment on soft ground with and ... · 2004/1/24 behavior of reinforced...

2004/1/24 Behavior of Reinforced Embankment on Soft Ground ... 1

Behavior of Reinforced Embankment on Soft Ground with and without

Jet Grouted Soil-Cement Piles

by1Dennes T. Bergado and 2Glen A. Lorenzo

1Professor and 2Doctoral Candidate, respectively Geotechnical Engineering Program

Asian Institute of Technology, Bangkok, THAILAND


Soil Profile along Bangkok-Chonburi

SOFT CLAY

MEDIUM CLAYSTIFF CLAY


Failure of Embankment on Soft Ground


Problem of Bridge Approach on Subsiding Ground


Basal Reinforced Piled Embankments

Transition between non-piled and piled foundations


Prevent slope failures and settlement of embankment

and structure Increase stability of slopes

Increase horizontal resistance of structures

Reduce settlement and prevent slope failures of bridge’s

abutments

Some Applications of Soil-Cement Piles(DJM Research Group, 1984)


It can significantly increase the strength and reduce the compressibility of soil.Soil improvement can be attained at optimum period of only 1 month.

Cement is abundant and cheaper in Asia.

Cement is effective than lime.

Advantages of Soil-Cement Stabilization


THE SITEFull-Scale Embankment on DMM Piles (Jet grouting)


Soil Profile at the Site (Jet grouted piles)

12 14 16 18 20Unit weight (kN/m3)

0

1

2

3

4

5

6

7

8

9

10

11

Dep

th (m

)

2.6 2.65 2.7 2.75 2.8Gs

Unit weightGs

20 40 60 80 100120PL, wN, LL

PL wN LL

0 20 40 60 80Corrected Su(kPa)

from Vane Sheat Test

0 50 100 150 200P' oand P'max (kPa)

Clay backfill

Weathered clay

Soft clay

Medium stiff clay

P'o P'max


Jet Grouting Machine

Jet pressure = 20 MPa


Sequence of Soil-Cement Piles Installation

(1)Positioning

(2) Penetration

(Remolding)(3) Completion of penetration

(4) Feeding of cementing agent (withdrawal)

(5) Completion


Plan View and Layout of DMM Piles


Front Elevation and DMM Pile Penetration


6 m 6 m

4 m

HEXAGONAL WIREMESH REINFORCEMENT

9 m

6 m

DUMMY REINFORCEMENT FORFIELD PULL-OUT TEST

WELL COMPACTED AYUTHAYA SAND BACKFILL

VERTICAL PRE-CASTCONCRETE FACING

1m WEATHERED CRUST

SOFT CLAY

MEDIUM STIFF CLAY

3 m

3 m

15 m depth

0.6 m DIAMETER SOIL- CEMENTPILES AT 1.5 m SPACINGIN SQUARE PATTERN

EXTENSOMETERSUPPORT

EXTENSOMETER WIRES

1.5m CLAY BACKFILL

PIEZOMETERBOARD

6 @ 1.5m = 9m 2m 1m

SETTLEMENT REFERENCE

8m

6m

3m

PIEZOMETERS REFERENCE

17m 6m 14.5m 2m 1.5m

P1-P5

P1-P5

P1-P5

P6 P7 P8

P6 P7 P8

P6 P7 P8

S5/S1 S6/S2 S7/S3 S8/S4

NOTE: PLEASE SEE THE PLAN VIEW FOR DETAILS OF THE LOCATION OF OTHER INTRUMENTATION POINTS

DS1 DS2 DS3

DS6 DS7 DS8

Section thru Center Line


Instrumentations and Laying of Reinforcements


Reinforcement Connection


Hexagonal Wire Mesh

WidthLength

Basic hexagonal wire mesh reinforcement geometry

Cross section of different types of hexagonal wire mesh reinforcement

Zinc Coating

Steel core wire

PVC CoatingZinc Coating

Steel core wire


Deformation and Necking Phenomenon of Hexagonal Wire Mesh Reinforcement during Pullout (Conventional pullout test)

Hexagonal cell in the centerline of thereinforcement

Hexagonal cell at the edge of thereinforcement


Modified Pullout Test Set Up(In-soil Pullout Test)

Outer Clamps

Boundary of Large ScalePullout Box Apparatus

PulloutDirection

In-soil ClampsSteel Rods


Pullout Test Apparatus (Maccaferri, 1997)


0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140 160Applied normal pressure (kPa)

Max

imum

pul

lout

load

(kN

/m)

Maccaferri (1997)Kongkitkul (2001), L = 0.70 mKabiling (1997), L = 1.10 mKabiling (1997), L = 0.90 mKabiling (1997), L = 0.70 m

Tult = 44.8 kN/m (in-air tensile test)

Maximum Pullout Resistance in Various Pullout Test Programs


The Finished 6m High Reinforced Embankment


Surface Settlement(hollow symbol= “on clay”; solid = “on pile”)

02468

0 60 120 180 240 300 360 420

Fill

heig

ht (m

)

050

100150200250

300350400

0 60 120 180 240 300 360 420Time (Days)

Set

tlem

ent (

mm

)

S1 S2S5 S6S10 S11S14 S15

Sp =1200mm (Untreated ground)

Sp (ave.) =325mm (improved ground)


Differential Settlement between Soil and Pile (hollow symbol= “on clay”; solid = “on pile”)

050

100150200250

300350400

0 60 120 180 240 300 360 420Time (Days)

Set

tlem

ent (

mm

)

S1 S2S5 S6S10 S11S14 S15

25mm60mm

click


Horizontal Inclinometer H1 (on pile)

400

350

300

250

200

150

100

50

0

0 2 4 6 8 10 12 14 16 18 20 22

29.Jan 05.Feb 09.Feb 12.Feb 13.Feb 15.Feb 23.Feb

Distance (m) S

ettle

men

t (m

m)

Started on Jan 28Ended on Feb 12


Horizontal Inclinometer H2 (on clay)

400

350

300

250

200

150

100

50

0

0 2 4 6 8 10 12 14 16 18 20 22

29.Jan 05.Feb 09.Feb 12.Feb 13.Feb 15.Feb

Distance (m)Se

ttlem

ent (

mm

)


Predicted vs. Measured Settlement

02468

Fill

ht. (

m)

050

100150200250300350400450

0 50 100 150 200 250 300 350 400 450 500

Time (days)

Settl

emen

t (m

m)

Field monitoring, [S2 at the Center], on pileField monitoring, [S6 at the Center], on groundUntreated ground (1D method)Lorenzo and Bergado (2003), on pileLorenzo and Bergado (2003), on clayAsaoka's method on clay


Steel-Grid Reinforced Embankment on Unimproved Ground

Soil Profile at the Site


Steel-Grid MSE Embankment on Unimproved Soft Foundation


Front Elevation (unimproved foundation)


Section View (unimproved foundation)


Pullout Friction Resistance of Steel Grid


Pullout Bearing Resistance of Steel Grid


Comparison of Lateral Displacement Profiles(with and without jet grouted piles)

0 100 200 300 400 500Lateral movement (mm)

-14-13-12-11-10-9-8-7-6-5-4-3-2-10123456

Dep

th (m

)

With jet grouted piles (TE2), after constructionWith jet grouted piles (TE2), 7 months after const'n No improvement (TE1), after constructionNo improvement (TE1), 7 months after const'n

Wall face

Backfill/Weathered clay

Soft clay

Medium to Stiff Clay


Comparison of Surface Settlements(with and without jet grouted piles)

0 5 10 15 20Horizontal distance (m)

0100200300400500600700800900

100011001200130014001500

Surf

ace

settl

emen

t (m

m)

FACE TOEEMBANKMENT

With jet grouted piles (TE2), after constructionWith jet grouted piles (TE2), 1 year after const'nNo improvement (TE1), after constructionNo improvement (TE1), 1 year after const'n


Settlement Reduction and Rate of Settlement

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.000 300 600 900 1200

Time (Days)

Settl

emen

t (m

)

Finite elementFinite elementSS6Untreated, 1-D conventional

Sp =1200mm (Untreated ground)

Click to location of SS6


0 10 20 30 40 50 60

-505

10152025303540

p1/6 p2/6 p3/6 p4/6 p5/6 p6/6 p7/6 p8/6

Exc

ess

pore

pre

ssur

e (k

Pa)

Time (days)

012345678

Hei

ght (

m)

Faster Rate of Consolidation of Improved Ground

Within the improved ground (55% dissipated)

Outside the improved ground (35% dissipated)

3 m

3 m

OARD

P1-P5

P1-P5

P1-P5

P6 P7 P8

P6 P7 P8

P6 P7 P8

S5/S1 S6/S2 S7/S3 S8/S4

DS1 DS2 DS3

DS6 DS7 DS8

Excess Pore Pressure in Clay at 6m Depth

click


One-Dimensional and Unconfined Compression of Cement-Admixed

Clay of Higher Water Content


Properties of the Base Clay Bangkok Clay


Definition of higher water content clay:

A clay that has a natural water content equal to or greater than its liquid limit (LL),or a clay that has been remolded to water content equal to or greater than its LL.


Conceptual Diagram of Cement Stabilized Clay at Higher Water Content

Prolong curing

Better dispersion of cementing agents/ions within the pores. It is expected to yield higher strength ….Higher permeability and good drainage ability.


Laboratory Test

Remolding the base clay at clay water contents from liquid limit (LL) to 2LL.

Water/cement ratio of slurry of 0.6.

Curing the specimens directly in the oedometer rings for oedometer tests, and in the PVC mold for UC tests.

Curing the specimen in the humid room within 7, 14 and 28 days; only 28 days for oedometer tests.


Post-Yield Compression Lines (5% and 10% cement)(measured values vs. predicted values)

10 100 1000 10000

Effective stress, σv' (kPa)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Vo

id r

ati

o,

eb) 10% Cement content; 100% to 250% remolding water content

10 100 1000 10000


1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Vo

id r

ati

o,

e

a) 5% Cement content; 130% to 200% remolding water content

Remolding Symbol water content (%)

250200160130100UndisturbedIntrinsic

Generated postyield compression line


10 100 1000 10000


1.01.52.02.53.03.54.04.55.05.5

Void

ratio

, e

c) 15% Cement content; 100% to 200% remolding water content

Remolding ymbol water content (%)

250200160130100UndisturbedIntrinsic

Generated postyield compression line

Post-Yield Compression Lines (15% cement)(measured values vs. predicted values)


Normalized Post-Yield Compression Curves

Normalizing parameterIvnc = (et - et,1600)/C*

ctwhere:

et = void ratio of treated sample at certain effective stress, σ’v;

et1600 = void ratio of treated sample at effective stress of 1600 kPa for certain cement content;

C*ct = mean slope of the post-

yield compression line for certain cement content.

Fitted curveIvnc= -0.06(logσ'v)3 +0.59(logσ'v)2

– 2.76(logσ’v) + 4.74;

in similar form of ICL of Burland(1990).

10 100 1000 10000


-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0M

od

ifie

d v

oid

in

de

x,

I vn

cSymbol Cement content 15% 10% 8% 5% 3% Intrinsic Fitting curve


Schematic Diagram for Predicting Compression Line of Cement Treated Clay (curing time: at least one month)

eot = initial void ratio after curing;σvy = predicted vertical yield stress.Swelling index

10 100 1000 10000

Vertical yield stress, σvy (kPa)

0.51.01.52.02.53.03.54.04.55.05.5

Voi

d ra

tio a

fter

curi

ng, e

ot

5% 10%15%20%

Cement content, Aw

10 100 1000 10000Effective stress, σv' (kPa)

1.01.52.02.53.03.54.04.55.05.5

Void

ratio

, e

eot,1

Post-yield compressionline for particular cementcontent

eot,2

σvy,1

σvy,2

Increasing Aw


Coefficient of Permeability from Oedometer Test of Untreated and Cement-Treated Soft Bangkok Clay

0.01 0.1 1 10 100 1000

Permeability, kv (x10-10m/s)

0.51.01.52.02.53.03.54.04.55.05.56.0

Void

rati

o, e

e = 1.2Log(k) + C

e = 1.2Log(k) + 2.0

C=2.5 C=1.5

Symbol Cement content 15% 10% 8% 5% Intrinsic Undisturbed

Note: k x 10-10 m/s


Unconfined Compression Tests

0.0 0.5 1.0 1.5 2.0 2.5

Axial strain (%)

0100200300400500600700800900

100011001200

UC

stre

ngth

, qu(k

Pa)

Note: *= remolding water content

+= cement content100-20100-15100-10100-5130-20130-15130-10130-5160-20160-15160-10160-5

Base clay

28 days curing

0 0.5 1 1.5 2 2.5

Axial strain (%)

0100200300400500600700800900

100011001200

UC

stre

ngth

, qu(k

Pa)

14 days curing


Unconfined Compression Tests (cont’d)

wA/wcu BAq =

A = f (time, clay type, etc.) = intercept

B = f (clay type, etc.) = slope

2 6 10 14 18 22 26 30 34

Clay water/cement content ratio, wc/Aw

10

100

1000

UC

stre

ngth

, qu(k

Pa)

Curing28 days14 days7 days

wA/wcu BAq =

2 6 10 14 18 22 26 30 34

Clay water/cement content ratio, wc/Aw

0100200300400500600700800900

1000

UC

stre

ngth

, qu(k

Pa)

Curing28 days14 days7 days


Modulus of Elasticity versus UC Strength(Laboratory mix cement-treated Bangkok clay)

150 300 450 600 750 900 10500

20

40

60

80

100

120

140

160

180

200

Initial tangent modulus, E i Secant modulus, E 50

E i = 121qu

W in (1997)E i = 115qu

Horpibulsok (2001)

E 50 = 147qu

R 2 = 0.986

E 50 = 114qu

W in (1997)

E i = 175qu

R 2 = 0.985

Mod

ulus

of d

efor

mat

ion

E i , E 50

(MPa

)

Unconfined compressive strength, qu (kPa)


Vertical Yield Stress σvy versus UC Strength qu of Cement-Treated Bangkok Clay and Ariake Clay

0 200 400 600 800 10001200

Unconfined compressive strength, qu(kPa)

0200400600800

1000120014001600180020002200

Ver

tical

yie

ld st

ress

, σvy

' (kP

a)

σvy= 1.27qu(kPa)Kamon and Bergado (1991)Ariake clay

σvy= 1.4qu(kPa) Bangkok clay, 28 days curing Bergado and Lorenzo (2002)

Test data, 28 daysTest data, 14 days

σvy= 1.55qu(kPa) Bangkok clay 14 and 28 days curing This study


Optimum Mixing Clay Water Content

Optimum mixing clay water content (wopt) is hereinafter defined as the total clay water content (or mixing clay water content) of the clay-cement paste that would give the highest possible improvement in strength of cured cement-admixed clay.


Effect of Mixing Clay Water Content on Unconfined Compression (10% Cement Content)

0 1 2 3 4 5

Axial strain (%)

0100200300400500600700800900

100011001200

Unc

onfin

ed c

ompr

essi

ve st

reng

th, q

u(kPa

)

28 days curing

105%135%165%80%

Total clay water content


Effect of Mixing Clay Water Content on 1-Dimensional Compression (10% Cement)

10 100 1000 10000


1.0

1.5

2.0

2.5

3.0

3.5

4.0

Voi

d ra

tio, e

165%135%105%80%

Total claywater content


Typical Strength Curve of Cement-Admixed Clay(to get the optimum mixing clay water content)

60 80 100 120 140 160 180

Total clay water content, cw (%)

100

200

300

400

500

600

700

800U

ncon

fined

com

pres

sion

stre

ngth

, q u

(kPa

) cw=LLcw=1.15LL


CONCLUSIONS

1) Two full-scale reinforced embankments were constructed on soft ground.

The first embankment (TE1), 5.7m high and reinforced with steel-grids, was constructed on unimproved ground.The second embankment (TE2), 6.0m high reinforced with hexagonal wire reinforcement, was constructed on jet grouted soil-cement piles improved ground.


CONCLUSIONS (cont’d)

2) After embankment construction, the maximum lateral movements in the unimproved soft foundation soil was 130mm, while that of improved foundation soil was only 5mm.Therefore, the installation of soil-cement piles has effected significant increase in the lateral resistance and the bearing capacity of the foundation soil.



3) One year after embankment construction, the maximum surface settlement of TE1 was 1.0m while that of TE2 was only 0.325m. Therefore, the soil-cement pile installation in the soft foundation has also effectively reduced the settlement by at least 70%.

4) Also, one year after construction the unimproved foundation was far from its 90% consolidation, but the soil-cement piles improved ground was already close to its 90% consolidation.



5) The maximum lateral movement of the reinforced embankment on soil-cement piles improved ground was lower than that of reinforced embankment on unimproved foundation.

6) The existence of optimum mixing clay watercontent (wopt) has been proven from the results of UC tests and oedometer tests of cement-admixed clay.



7) wopt was found to fall within liquid limit (LL) up to 1.15LL of the base clay.

8) At optimum mixing clay water content, only 10% cement content by weight is needed instead of 17% in the conventional method to obtain a UC strength of 650 kPa, with consequent 40% cost reduction.


Layout of Settlement Plates


Location of Piezometers

3 m

3 m

EZOMETEROARD

6 @ 1.5m = 9m 2m 1m

P1-P5

P1-P5

P1-P5

P6 P7 P8

P6 P7 P8

P6 P7 P8

S5/S1 S6/S2 S7/S3 S8/S4

THE AILS

DS1 DS2 DS3

DS6 DS7 DS8

behavior of reinforced embankment on soft ground with and ... · 2004/1/24 behavior of reinforced...

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