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Improved performance of soft clay foundations using stone columns

and geocell-sand mattress

Sujit Kumar Dash a Mukul Chandra Bora b

a Department of Civil Engineering Indian Institute of Technology Kharagpur Kharagpur 721 302 Indiab Department of Civil Engineering Indian Institute of Technology Guwahati Guwahati 781 039 India

a r t i c l e i n f o

Article history

Received 23 November 2012

Received in revised form

23 August 2013

Accepted 31 August 2013

Available online 21 September 2013

Keywords

Foundation

Geosynthetics

Stone columns

Ground improvement

a b s t r a c t

A series of experiments have been carried out to develop an understanding of the performance

improvement of soft clay foundation beds using stone column-geocell sand mattress as reinforcement It

is found that with the provision of stone columns of adequate length and spacing about three fold

increases in bearing capacity can be achieved While with geocell-sand mattress it is about seven times

that of the unreinforced clay But if combined together the stone column-geocell mattress composite

reinforcement can improve the bearing capacity of soft clay bed as high as by ten fold The optimum

length and spacing of stone columns giving maximum performance improvement are respectively 5

times and 25 times of their diameter The critical height of geocell mattress can be taken equal to the

diameter of the footing beyond which further increase in bearing capacity of the composite foundation

bed is marginal

2013 Elsevier Ltd All rights reserved

1 Introduction

Rapid urbanisation and growth of infrastructure in the present

days has resulted in dramatically increased demand for land space

This has compelled the building industry to improve the soft soil

grounds which otherwise are unsuitable for construction activities

Amongst the various ground improvement techniques used stone

columns and geosynthetic reinforcement are probably the most

popular ones This is primarily due to their simplicity ease of

construction and overall economy that 1047297nds favour with the

practicing engineers

A stone column is a column of stones made through opening up

a vertical cylindrical hole in the soft clay bed and subsequently

1047297lling it up with compacted stone aggregates Due to higher

strength and stiffness the stone columns sustain larger proportion

of the applied load than their soft soil counterpart leading tosigni1047297cant performance improvement of foundation beds (Hughes

and Withers 1974 Juran and Guermazi 1988 Christoulas et al

2000 Wood et al 2000 McKelvey et al 2004 Ambily and

Gandhi 2007 Black et al 2007 Cimentada et al 2011 Dash and

Bora 2013) Moreover being highly permeable the stone columns

act as vertical drains facilitating consolidation of the soft clay

around and thereby improving the long term performance of the

foundation system

Geocell reinforcement is a latest development in the avenues of

geosynthetics It is a three dimensional polymeric honeycomb like

structure of cells interconnected at joints that the reinforcing

mechanism is primarily through all-round con1047297nement of soils

Besides geocells intercept the potential failure planes and their

rigidity forces them deeper into the foundation soil This induces a

higher surcharge loading on the failure plane giving rise to

increased load carrying capacity (Webster and Watkins 1977 Bush

et al 1990 Cowland and Wong 1993 Dash et al 2001 2003a

2003b 2004 Zhou and Wen 2008 Sireesh et al 2009

Leshchinsky and Ling 2013 Tanyu et al 2013)

Review of literature shows that geocell-sand mattress and stone

columns are effective means of performance improvement of soft

clay foundations Their individual applications though have been

intensely studied but combined application of both has remained

unexplored It is expected that the geocell-sand mattress with stonecolumns underneath shall further enhance the load carrying ca-

pacity of the foundation system Moreover a cushion of sand is

generally provided over the stone columns for the purpose of

drainage Limited research reported in the literature indicates that

this sand layer when reinforced with planar geosynthetics can

noticeably improve the bearing capacity of the foundation system

(Deb et al 2007 Abdullah and Edil 2007 Deb et al 2011) Arulrajah

et al (2009) have reported the use of a geogrid-soil platform over

stone columns in the construction of high speed railway embank-

ments in Malaysia In this arrangement the reinforced soil cushion

serves as a 1047298exible raft over the stone columns similar to that of a Corresponding author Tel thorn91 3222 282418 fax thorn91 3222 282254

E-mail address sujitciviliitkgpernetin (SK Dash)

Contents lists available at ScienceDirect

Geotextiles and Geomembranes

j o u r n a l h o m e p a g e w w w e l s e v i e r co m l o c a t e g e o t e x m em

0266-1144$ e see front matter 2013 Elsevier Ltd All rights reserved

httpdxdoiorg101016jgeotexmem201309001

Geotextiles and Geomembranes 41 (2013) 26e35



piled raft system leading to improved load capacity However geo-

cell is a superior form of reinforcement over the planar one ( Dash

et al 2004 Madhavi and Vidya 2007 Latha and Somwanshi

2009) This is mostly due to its three dimensional con1047297ning struc-

ture that prevents lateral spreading of soil Therefore the sand

cushion over the stone columns if reinforced with geocells is ex-

pected to produce enhanced performance improvement These as-

pects are studied herein through a series of laboratory-scale model

tests The results have been analysed in developing an under-

standing of the behaviour of clay foundations reinforced with the

stone column-geocell mattress composite system

2 Details of model tests

21 Planning of experiments

Schematic sketch of a typical test con1047297guration is shown in

Fig 1 The stone columns were left 1047298oating in the clay bed This was

to simulate the situation commonly encountered in coastal areas

wherein soft clay deposits extend over very large depths that the

stone columns are generally terminated in the clay itself The col-

umns were placed in triangular pattern at a regular spacing S

(Fig 2) In all the tests diameter of stone columns (dsc) was kept

constant as 100 mm

Geocells were formed in chevron pattern (Fig 3) as it gives

better performance improvement over the diamond pattern (Dash

et al 2001) Diameter of geocells (dgc) taken as equivalent diam-

eter of geocell pocket opening was kept constant as 08D

throughout (D diameter of footing) The geocell mattresses were

placed at a constant depth (u) of 01D from the base of the footing

which was found to be the optimum location giving maximum

performance improvement (Dash et al 2008)

In total twelve series of model load tests were conducted the

details of which are presented in Table 1 Within each series onlyone parameter was varied This was to understand the in1047298uence of

this particular parameter on the overall behaviour of the founda-

tion system while the others were kept constant Tests in series 1

were performed on unreinforced clay beds Series 2 and 3 consisted

of testing the stone column reinforced clay beds wherein the in-

1047298uence of length (L) and spacing (S ) of the columns werestudied In

all these tests there was no sand cushion over the clay beds The

effect of height of geocell-sand mattress (h) was studied under

series 4 Subsequently tests in series 5e12 were designed to

LStone

column

Clay

Sand h

u

Geocell layer

DT DTDT DTDT DTDTDT

Footing

D D D

(00) xDxD

Fig 1 Schematic diagram of test con1047297guration

S

dsc

S

Stone column

Fig 2 Layout of stone columns

transverse member diagonal member

bodkin joint

b

b

Fig 3 Geocell system in chevron pattern plan view

Table 1

Details of model tests

Testseries

Typeof reinforcement

Details of parameters investigated

1 Un rei nforc ed cl ay bed wi th c u of 5 kPa

2 SC Variable parameter Ldsc frac14 1 3 5 7

Constant parameter S dsc frac14 25

3 SC Variable parameter S dsc frac14 15 25 35

Constant parameter Ldsc frac14 5

4 GC Variable parameter hD frac14 053 09 11 16

Constant parameter dgcD frac14 08 bD frac14 6

5 GC thorn SC Variable parameter Ldsc frac14 1 3 5 7

Constant parameter

hD frac14 053 dgcD frac14 08 bD frac14 6 S dsc frac14 25


Constant parameter



Constant parameter



Constant parameter


9 GC thorn SC Variable parameter S dsc frac14 15 25 35

Constant parameter

hD frac14 053 dgcD frac14 08 bD frac14 6 Ldsc frac14 5


Constant parameter



Constant parameter



Constant parameter


Note SC Stone columns GC Geocell-sand mattress

SK Dash MC Bora Geotextiles and Geomembranes 41 (2013) 26 e 35 27



investigate the combined application of both the reinforcements

ie stone columns and geocell-sand mattress

22 Materials used

The model clay beds were prepared using a locally available soil

that had 70 fractions 1047297ner than 75 mm (Fig 4) Its liquid limit

plastic limit and plasticity index were found to be 40 21 and 19

respectively (ASTM D4318 2005) As per the Uni1047297ed Soil Classi1047297-

cation System (USCS ASTM D2487 2006) the soil can be classi1047297ed

as clay with low plasticity (CL)

The stone columns were formed out of a poorly graded crushed

granite aggregate with particle sizes in the range of 2e10 mm (d10

d30 d50 of 220 315 490 mm respectively Fig 4) and uniformity

coef 1047297cient of 232 Its direct shear friction angle (peak) at place-

ment density of 153 kNm3 was found to be 48 The diameter of

model stone columns (100 mm) and size of aggregates used

(d50 frac14 49 mm) were approximately in 17 scale representation of

prototype stone columns of 700 mm diameter with averageaggregate size of 35 mm

The geocell reinforcement used was fabricated from a biaxial

geogrid having aperture size of 36 mm 36 mm ultimate tensile

strength of 193 kNm and 5 strain secant modulus of 135 kNm

(ASTM D6637 2001) The joints of the geocells formed out of 6 mm

wide and 3 mm thick polypropylene strips had a tensile strength of

475 kNm (ASTM D4884 2009) Such low strength of joints was

adopted to scale down the overall strength of the geocells that it is

suitable for the model tests The geocells were 1047297lled with a poorly

graded sand that had average particle size of 044 mm and uni-

formity coef 1047297cient of 252 (Fig 4) In all the tests the sand was

placed at 80 of relative density Its peak friction angle obtained

through triaxial compression tests in the pressure range of 100e

200 kPa was 44

23 Test setup

The model tests were carried out in a laboratory scale test bed-

cum-loading frame assembly (Fig 5) The test beds were prepared

in a steel tank of 1000 mm long1000 mm wide and 1300 mm high

To avoid yielding during tests the four sides of the tank were

braced laterally on their outer surfaces with steel channels The

footing used was made of a rigid steel plate and measured 150 mm

in diameter (D) In order to create a rough base condition a thin

layer of sand was glued onto its bottom In all the tests the footing

was placed at the centre of the test tank Loading was applied

through an automated hydraulic jack system supported against a

reaction frame 1047297

xed onto the ground The load transmitted to the

footing was recorded through an electronic load cell of 20 kN ca-

pacity with an accuracy of 001 N The settlements of the footing

were measured by two linear variable differential transducers

(LVDTs) placed at diametrically opposite ends (DT1 DT2 Fig 1)Deformations (heavesettlement) on foundation bed too were

measured by LVDTs placed through small plastic strips on the soil

surface (DT3eDT8 Fig 1) The LVDTs were of 50 mm travel with an

accuracy of 3 microns The load cell and the LVDTs were connected

to a computer controlled data acquisition system

Selig and McKee (1961) and Chummer (1972) have observed

that the failure wedge in the foundation bed extends over a dis-

tance of about 2e25 times the footing width away from its centre

In the present tests the distance of tank walls from centre of footing

being more than 33D the slip planes are not likely to be interfered

with Besides the geocell mattress being 1047298exible deforms down-

ward under the footing loading and thereby gets pulled away from

the tank side walls reducing the boundary effect to a practically

negligible value Indeed Dash et al (2003a) through instrumentedmodel tests have observed that the footing loading in nearly

similar test conditions did not induce any additional pressure on

the tank walls

The stone columns used had a maximum length of 700 mm (ie

L frac14 7dsc) and the geocell mattresses used had maximum height of

255 mm (ie h frac14 17D) Therefore the minimum clear spacing be-

tween the stone column base and the tank bottom maintained in

the tests was 345 mm [ie 1300 (700 thorn 255)] This is about 345

times the diameter of the stone column (dsc) Mayerhof and Sastry

(1978) have observed that the failure zone below a rigid pile ex-

tends over a depth of about 2 times its diameter The stone columns

being 1047298exible this depth would further be less A stress analysis

considering the dispersion in geocell mattress (Dash et al 2007)

and group action of stone columns (similar to that of rigid piles in

clay Bowel1988) was carried out It shows that for height of geocell

mattress of 17D and stone column length of 7dsc the stressinduced

at the bottom of the test-tank was less than 2 of the applied

pressure In view of this it can be said that the test-tank used in the

present investigation was considerably large enough and not likely

to interfere with the failure zones and hence the experimental re-

sults Besides the con1047297nement due to the tank walls simulated the

actual 1047297eld conditions for the interior columns in a large group

(Ambily and Gandhi 2007)

24 Test bed preparation

The clay was pulverised mixed with predetermined amount of

water and for moisture equilibrium was kept in airtight containers

0001 0010 0100 1000 10000 100000

Particle size (mm)

0

20

40

60

80

100

P e r c e n

t f i n e r b y w e i g h t

stone aggregate

sand

clay

Fig 4 Particle size distribution of stone aggregate sand and clay soil

Fig 5 Test set-up

SK Dash MC Bora Geotextiles and Geomembranes 41 (2013) 26 e 3528



for about a week The test bed was prepared in lifts of 005 mthickness For each lift the amount of soil required to produce the

desired bulk density was weighted out placed in the test-tank

levelled and compacted Compaction was done through a wooden

board and a drop hammer using depth marking on the sides of the

tank as guide The compaction energy applied was 299 kJm3 Un-

disturbed soil samples were collected from different locations and

their properties were evaluated Sampling was done through a thin

cylindrical sampler that was pressed into the clay bed andextracted

out with the soil withinApartfrom the in situ density and moisture

content the specimens were tested for the vane shear strength as

well The average moisture content degree of saturation bulk unit

weight and shear strength of the clay in the test beds were found

to be 36 100 1805 kNm3 and 5 kPa respectively Their coef 1047297-

cient of variability was in the range of 15The stone columns were constructed by a replacement method

An open-ended stainless steel pipe of 100 mm outer diameter and

15 mm of wall thickness smeared with petroleum jelly (to reduce

friction) was pushed into the clay bed until it reached the depth of

the column to be formed Subsequently the clay within the pipe

was scooped out through a helical auger of 90 mm diameter To

minimise suction effect a maximum of 100 mm was removed at a

time On completion the internal wall of the pipe was cleaned and

stone aggregates were charged in The stones were added in

batches of 06 kg and compacted to height of 50 mm through a

circular steel tamper of 09 kg with 30 blows of 200 mm drop

leading to a density of 153 kNm3 that corresponds to 65 of

relative density The pipe was then slowly raised ensuring a mini-

mum of 25 mm overlap within the aggregate that the clay outsidedoesnrsquot intrude in This procedure was continued until the stone

column was completely formed (ie till top of clay bed) The stone

column reinforced clay bed thus formed was loaded with a seating

pressure of 25 kNm2 over the entire area for 4 h This was to

achieve uniformity in the test bed (Malarvizhi and Ilamparuthi

2007)

The geocell reinforcement was prepared from geogrid strips

placed in transverse and diagonal directions and connected

together with bodkin joints (Bush et al 1990) The jointwasformed

by pulling the ribs of the diagonal geogrid up through the trans-

verse geogrid and slipping a dowel (plastic strip) through the loop

created (Carroll and Curtis 1990) Three-dimensional view of a

typical geocell structure placedover the clay bed is shown in Fig 6

The geocells were 1047297

lled with sand through raining Compared to

unreinforced case with geocell reinforcement the height of raining

required to achieve the target density was relatively more how-

ever the difference was not much This was because the geocells

being made of geogrids had more than 80 of open area thereforedid not affect much the free 1047298ow of sand during raining The dif-

ference in the placement densities of the sand at various locations

in the test bed measured through in situ sampling was found to be

less than 15

25 Test procedure

In all the tests loading was applied in strain controlled manner

at the rate of 2 mmmin This relatively faster rate of loading was

intended to produce undrained response in the saturated clay bed

It is one of the worst 1047297eld conditions expected as in this case the

angle of friction of the soil tends to be zero leading to large

reduction in the bearing capacity Such phenomenon is common

during rainy seasons particularly in case of railways and highwayswhere the loading is transient in nature In all the tests load was

applied until the footing settlement reached 40 mm Through a

computer controlled system the load-deformation data were

continuously recorded

On completion of tests the deformed shape of the stone columns

were mapped This was done through careful removal of stone

aggregates and 1047297lling the shaft with Plaster of Paris (CaSO4$05H2O)

paste After being hardened the Plaster of Paris column was taken

out and measured for its shape and size The stone column de-

formations thus obtained are presented in terms of radial strain

(r d r o)r o wherein r d is the deformed radius and r o is the original

radius

3 Results and discussion

Typical pressure-settlement responses of clay bed alone that

with geocell and geocell-stone column composite reinforcement

are presented in Fig 7 The settlement s reported is the average of

the readings taken at both ends of the footing (DT 1 and DT2 Fig 1)

It could be observed that in case of unreinforced clay the slope of

the pressure-settlement response continues to increase until set-

tlement (sD) of about 15 and thereafter tends to become nearly

vertical This means that the soil has undergone clear failure and

therefore couldnrsquot support additional pressure anymore However

with geocell reinforcement (Clay thorn GC) the bearing pressure con-

tinues to increase even at settlement (sD) as high as 25 although

the overall improvement is relatively less But with stone columns

in the clay subgrade underneath geocell mattress (Clay thorn GC thorn SC)

Fig 6 Typical geocell layer in the test bed

0

4

8

12

16

20

24

28

F o o t i n g s e t t l e m e n

t s D

( )

0 20 40 60 80 100 120 140 160

Bearing pressure (kPa)

Clay

Clay+GC

Clay+GC+SC (Ldsc= 1)




Fig 7 Footing pressure-settlement responses in1047298uence of length of stone columns in

composite foundation bed (hD frac14 053 S dsc frac14 25) e Test series 5




the bearing capacity has improved signi1047297cantly much higher than

that with geocell mattress alone Besides the stiffness of the

foundation bed too has increased substantially indicated through

reduced slope of the pressure settlement response Similar

behaviour is noticed in all other cases as well This is attributed to

the increased resistance against deformation provided by the stone

columns through mobilisation of friction and stiffness of the stone

aggregates that provides additional support to the geocell mattress

As a result of which the geocell-sand mattress that behaves as a

subgrade supported beam (Dash et al 2007) stands effectively

against the footing loading leading to improved performance of thefoundation system

The increase in the bearing capacity due to stone columns

geocell mattress and stone column-geocell mattress composite

reinforcement is quanti1047297ed through nondimensional improvement

factors IFsc IFgc IFgcsc respectively de1047297ned as the ratio of bearing

pressure with reinforcement (qsc qgc qgcsc) to that of unreinforced

clay bed (qu) both taken at equal settlement of footing ( sD) The

values of these improvement factors for different test cases and

footing settlements are presented in Table 2 It is evident that with

stone columns the bearing capacity of soft clay can be enhanced by

37 fold (IFsc frac14 37 Test series 3) and with geocell reinforcement it

can be up to 787 fold (IFgc frac14 787 Test series 4) But if coupled

together (ie stone columns and geocell mattress) the composite

reinforcement can enhance the bearing capacity of the soft clay as

high as by 10 fold (IFgcsc frac14 102 Test series 12) Hence it can be said

that the stone column-geocell composite is a superior form of

reinforcement that can give better performance improvement over

the conventional ones ie stone column geocell mattress In1047298u-

ence of different parameters on the overall performance of such

composite foundation systems are discussed in the following

sections

31 In 1047298uence of length of stone columns

In1047298uence of length of stone columns (L) in the composite

foundation bed has been studied for four different heights of

geocells h frac14 053D 09D 11D and 16D (Test series 5e8) It is of

interest to note that increasing the column length from 3 to 5 dsc

leads to sharp increase in performance both in terms of increased

load carrying capacity (IFgcsc Table 2) and reduced settlement

(Fig 7) However with further increase in length (L) to 7dsc the

additional improvement is much less Hence it can be said that in

the composite foundation system the optimum length of stone

columns giving maximum performance improvement is about 5

times their diameter (ie 5dsc) This observation however is from

small-scale models and needs to be veri1047297ed through prototype

tests The results are further analysed in terms of the improvement

factor ratios (ie IFgcscIFgc and IFgcscIFsc) that brings out the

Table 2

Bearing capacity improvement factors (IF IFsc IFgc IF gcsc)

Test series Reinforcement Variable parameter Bearing capacity improvement factor (IF)

sD 1 sD 5 sD 9 sD 13 sD 17 sD 21 sD 25 sD 27

2 SC Ldsc frac14 1 169 125 114 119 123 126 128 130

SC Ldsc frac14 3 181 154 153 160 162 166 173 173

SC Ldsc frac14 5 359 287 293 312 319 331 340 344

SC Ldsc frac14 7 369 320 317 337 340 348 356 360

3 SC S dsc frac14 15 366 290 320 345 349 361 367 370

SC S dsc frac14 25 359 287 293 312 319 331 340 344

SC S dsc frac14 35 197 147 167 184 181 186 190 193

4 GC hD frac14 053 134 150 164 186 195 211 226 232

GC hD frac14 09 210 218 283 303 335 359 411 433

GC hD frac14 11 290 410 477 557 600 660 712 739

GC hD frac14 16 420 481 543 614 654 708 764 787

5 GC thorn SC Ldsc frac14 1 172 198 191 201 215 230 246 253

GC thorn SC Ldsc frac14 3 187 222 223 236 248 266 288 295









GC thorn SC Ldsc frac14 5 566 665 663 700 740 801 850 874GC thorn SC Ldsc frac14 7 700 738 724 755 798 850 913 942





9 GC thorn SC S dsc frac14 15 454 482 484 495 516 553 579 588

GC thorn SC S dsc frac14 25 412 426 429 432 441 473 502 513










GC thorn SC S dsc frac14 35 510 629 643 700 750 819 882 906Note Boldface values indicate the maximum improvement factors for different reinforcements (ie SC GC and SC thorn GC)




contribution of individual reinforcement components (ie geocell

sand mattress stone columns) as has been explained below

IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)

Thus the factor (IFgcscIFsc) can be taken as the contribution of

geocell mattress sharing the surcharge loading in the composite

foundation system Similarly the factor IFgcscIFgc (ie qgcscqgc)

represents the contribution of stone columns Typical improvement

factor ratios IFgcscIFgc and IFgcscIFsc for the case with hD frac14 053

are depicted in Fig 8 and Fig 9 respectively It is evident that the

contribution of stone columns IFgcscIFgc increases with increase in

length and the improvement is the maximum when Ldsc ratio

changes from 3 to 5 This may be because the shorter columns (L

dsc lt 3) due to inadequate skin resistance have suffered punching

failure and therefore didnrsquot contribute signi1047297cantly towards the

load carrying capacity of the system In contrast the long columns

(Ldsc 5) owing to large skin resistance mobilised through

increased surface area have effectively stood against the footing

loading giving rise to visible increase in performance improvement

Further con1047297rmation of the column failure modes was obtained

from the post test deformation pro1047297les a typical of which for the

central stone columns are shown in Fig 10 It could be observed

that when short in length (Ldsc frac14 1 and 3) the bulging in the stone

columns is marginal indicating that the column has mostly been

punched down But with increase in length (Ldsc 5) it has

effectively stood against the footing and therefore has bulged

signi1047297cantly Furthermore with column Ldsc ratio of 1 the

contribution of geocell mattress IFgcscIFsc was the maximum

which however reduced as the column length increased and

remained almost constant for Ldsc 5 (Fig 9) This can be analysed

through the responses of the 1047297ll surface depicted in Fig 11 The

surface deformations (d) reported herein are the average of the

readings taken at distance D on both sides of the footing (DT5 andDT6 Fig 1) It can be seen that with increase in the length of stone

columns settlement (thornd) on the 1047297ll surface has reduced Corre-

spondingly heave in the adjacent region ( x frac14 2D and 3D) too was

found to have reduced This is attributed to the increased resistance

of stone columns that inhibits settlement and thereby heave in the

foundation bed With reduced deformations in the soil around the

strength mobilised in the geocells reduces and so is its contribution

to the performance improvement Stone column length beyond the

0 4 8 12 16 20 24 28

Footing settlement sD()

0

1

2

3

4

5

I m p r o v e m e n t f a c t o r r a t i o I F g c s c I F g c

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)

Fig 8 Improvement factor ratio-footing settlement responses contribution of stone

columns in composite foundation bed (hD frac14 053 S dsc frac14 25) e Test series 5

0 4 8 12 16 20 24 28


0

1

2

3

4

5

I m p r o v e m e n t f a c t o r r a t i o I F g c s c I F s c

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)

Fig 9 Improvement factor ratio-footing settlement responses contribution of geocell

mattress in composite foundation bed (hD frac14

053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7

L e n g t h o f s t o n e c o l u m n L d s c

0 5 10 15 20 25 30

Radial strain (rd-ro)ro ()

Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7

Fig 10 Post-test deformed pro1047297le of central stone column in composite foundation

beds (hD frac14 053 S dsc frac14 25) e Test series 5

0 4 8 12 16 20 24 28


0

1

2

3

4

5

A v e r a g e s u r f a c e d e f o r a m a t i o n

δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)

Fig 11 Surface deformation-footing settlement responses in1047298uence of length of stone

column in composite foundation bed ( xDfrac14

1 hD frac14

053 S dsc frac14

25) e

Test series 5




optimum (ie 5dsc) though enhances the skin resistance but it

mostly remains unutilised due to excessive bulging at the top As a

result the responses of the stone columns and that of the geocell

mattress beyond Ldsc ratio of 5 have almost been stabilised Thepresent 1047297ndings are in agreement with the observations of Hughes

and Withers (1974) McKelvey et al (2004) that increasing the

length of stone columns beyond a certain point adds little to the

increase in bearing capacity however can help reducing the set-

tlement in the foundation bed

32 In 1047298uence of spacing of stone columns

Effect of column spacing (S) in the composite foundation beds

was studied under Test series 9e12 Typical responses are shown in

Fig12 Itcan beseen thatat low settlements (sD lt 5) the slope of

the pressure-settlement plots with stone columns are much less

than the case without This indicates that when intact the stone

columns irrespective of their spacing have provided additionalstiffness to the foundation system This however was not the case

when the settlement was large primarily because the columns had

bulged

With relatively widely spaced stone columns (S frac14 35dsc) stiff-

ness of the composite foundation system is almost comparable to

that with geocell reinforcement alone (both the responses are

nearly parallel) It could be because at large spacing the group

action of the peripheral stone columns diminishes that they behave

as individual entities leading to reduced lateral resistance onto the

central con1047297ned region In the absence of adequate con1047297nement

from the surrounding the central stone column underneath the

footing bulged prematurely and therefore couldnrsquot enhance the

stiffness of the foundation system Indeed the post test observa-

tions have shown that with large spacing the central stone columnhad bulged more As the spacing reduces the group action in the

rings of stone columns builds up inducing con1047297nement in the

central region that provides increased support against column

bulging leading to enhanced performance improvement

In general the bearing capacity of the composite foundation bed

was more when the spacing of stone columns was less ( Fig 12)

However the improvement (IFgcsc) with the column spacing (S )

reducing from 35dsc to 25dsc was relatively more than that from

25dsc to 15dsc (Table 2 test series 9e12) Further analysis shows

that the contribution of stone columns in the composite system

IFgcscIFgc was the maximum when they were placed close

(S frac14 15dsc) and reduced as the spacing was increased (Fig 13) In

contrast when the stone columns underneath were placed wide

apart (S frac14 35dsc) the geocell mattress has carried maximum load

IFgcscIFsc which however reduced signi1047297cantly as the spacing of

columns was reduced to 25dsc (Fig 14) Under footing loading the

stone columns with wider spacing have deformed more As the

underlying support yields the geocell mattress through mobi-lisation of anchorage from the adjacent stable region bridges over

and thereby shares higher proportion of the surcharge pressure

The marginal difference in the load factor ratio IFgcscIFsc with the

spacing (S ) changing from 25dsc to 15dsc indicates that further

change in the contribution of geocell mattress is practically negli-

gible With reduced spacing increasedpercentage of weak clay gets

replaced by the stiffer stone columns This gives rise to more uni-

formity of stress in the foundation bed that it deforms less Indeed

reduced settlement and heave on the 1047297ll surface observed with

reduced spacing of stone columns testi1047297es that the deformations in

the foundation bed have reduced down As a result the strain in the

overlying geocell reinforcement reduces leading to reduced mobi-

lisation of its strength and stiffness In such case the geocell

mattress behaves more of like a pedestal a load transmittingmember Whereas with wider spacing (S frac14 35dsc) of stone col-

umns underneath it behaves as a load sustaining member like a

centrally loaded slab resting over columns It can therefore be said

that when the spacing reduces from 35dsc to 25dsc there is sig-

ni1047297cant change in the behaviourof stone columns that it shifts from

near isolated to an interacting response giving rise to large

improvement in the performance of the system Hence the opti-

mum spacing of stone columns in the composite foundation beds

can be taken as 25dsc

0

4

8

12

16

20

24

28

F o o t i n g s e t t l e m e

n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC

Clay+GC+SC(Sdsc= 15)



Fig12 Footing pressure-settlement responses in1047298uence of spacing of stone columns

in composite foundation bed (hD frac14 053 Ldsc frac14 5) e Test series 9

0 4 8 12 16 20 24 28


0

1

2

3

4

I m p r o v e m e n t

f a c t o r r a t i o I F g c s c I F g c





columns in composite foundation bed (hD frac14 09 Ldsc frac14 5) e Test series 10

0 4 8 12 16 20 24 28


0

1

2

3

4





Fig 14 Improvement factor ratio-footing settlement responses contribution of geo-

cell mattress in composite foundation bed (hD frac14

09 Ldsc frac14

5) e

Test series 10




33 In 1047298uence of height of geocell mattress

Typical responses of the composite system for three differentheights of geocell mattress (h frac14 053D 09D 16D) are shown in

Figs 8 9 13 14 15 and 16 respectively It could be observed that

when shallow in height (h frac14 053D) the geocell mattress has under

performed that the stone columns have shared nearly three times

more load (IFgcscIFgc frac14 3 Fig 8) However with increase in height

(h) the contribution of stone columns has reduced and that of

geocell mattress (IFgcscIFsc) has gone up When geocells are rela-

tively deep (h frac14 16D) the improvement factor ratio IFgcscIFgc is

just in the range of 1e12 (Fig 15) that the load carried by the stone

columns is at the most 20 that of the geocell mattress The data

presented in Fig 16 indeed shows such a response wherein the

value of improvement factor ratio IFgcscIFsc is as high as 65

indicating that most of the footing pressure has been sustained by

the geocell mattress A deep geocell mattress possesses highmoment of inertia that enables it to stand against the footing

penetration Besides with increase in height (h) the geocell area

deriving anchorage from the in1047297ll soil increases and so is the

anchorage resistance Therefore the geocell mattress takes a large

proportion of the footing loading on its own that the stone columns

underneath mostly remain dormant and thereby contribute less to

the performance improvement Visibly less bulging observed in the

post-test exhumed stone columns (Fig 17) establishes that they

indeed had under performed in sharing the surcharge loading

The improvement due to the geocell-stone column composite

reinforcements are summarised in Table 2 (Test series 5e12) It can

be seen that for height of geocell mattress h frac14 053D 09D 11D and

16D the maximum bearing capacity improvement IFgcsc frac14 569

747 942 and 102 respectively This highlights that the increase in

performance improvement with height of geocell mattress

increasing beyond 11D is relatively less A possible reason for this

could be the stress concentration induced local buckling and

yielding of geocells right under the footing that the global increasein strength and stiffness of the system due to increase in height of

the mattress remains immobilised Indeed the maximum differ-

ence in the values of the factor IFgcscIFsc (ie the load shared by the

geocell mattress) for the case with h frac14 16D and 11D was less than

5 Therefore height of geocell mattress equal to about the diam-

eter of the footing (h frac14 D) can be taken as the optimum one giving

maximum possible performance improvement in the composite

foundation beds However full-scale tests are required to verify this

observation

It is of interest to note that even geocell mattress of medium

height h frac14 09D when combined with stone columns can provide

bearing capacity improvement (IFgcsc frac14 746 Test series 6) as high

as that of a deep geocell mattress h frac14 16D (IFgcsc frac14 787 Test series

4) Due to practical constraints at times it might be dif 1047297cult to

accommodate a relatively large height geocell mattress In such

situation provision of stone columns in the underlying subgrade

would be a viable alternative to manage with geocell mattress of

relatively smaller height

4 Scale effect

Owing to reduced size model tests the results presented in this

paper are prone to scale effects Therefore further studies using

full-scale tests are required to verify these observations However

using a suitable scaling law the results from the present study can

be extrapolated to the prototype case (Fakher and Jones 1996)

The major physical parameters in1047298uencing the response of

geocell-stone column reinforced foundation systems can be

0 4 8 12 16 20 24 28


00

05

10

15

20

25

30


f c c t o r r a t i o I F g c s c I F g c

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30

Radial strain (rd - ro)ro ()

Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7






summarised as D h dgc K dsc L d50 S ɸ c u g G where ɸ is the

angle of internal friction of soil and stone aggregate K is the stiff-

ness of geocell reinforcement g is the unit weight of soil and

aggregate G is the shear modulus of the soil and aggregate Other

parameters have been de1047297ned previously The function ( f ) that

governs the composite foundation system can be written as

f

D h dgc K dsc L d50 S c ug Gf s qgcsc qu

frac14 0 (2)

It comprises of 15 parameters and has two fundamental di-

mensions (ie length and force) and therefore can be studied by 13

independent parameters (p1 p2 p3 p4p13 Buckingham

1914) Hence equation (2) can be written as

For a prototype footing ( p) with diameter n times that of the

model (m)

Dp

Dmfrac14 n (4)

For similarity to be maintained the p terms both for model and

prototype need to be equal and therefore considering the p9 term

Gp

Dpgpfrac14

Gm

Dmgm(5)

Assuming that the soils used in the model and prototype do

have same unit weight (Pinto and Cousens 1999) equation (5)

reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)

Considering similarity of the p10 terms

K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)

As can be seen the strength of prototype geocells should be of n2

times that of the model geocell where n is the scale factor The

geocells used in the present tests have tensile strength of 475 kN

m Therefore the results from the present study to be applicable in

practice the prototype geocells should have tensile strength of

475n2 kNm However the geometric parameters such as pocket

size and height of geocells length diameter and spacing of stone

columns etc have shown a linear variation with the footing size D

5 Conclusions

Review of literature shows that both geocell-sand mattress and

stone columns are effective means of reinforcing the weak soils

Their individual applications though have been intensely studied

by many researchers but combined application of both has

remained unexplored The experimental results obtained in the

present study con1047297rm that such composite reinforcement is an

added advantage over the conventional ones ie stone column or

geocell mattress With provision of stone columns the bearing

capacity of soft clay beds can be increased by 37 fold and with

geocell reinforcement it is of the order of 78 fold When coupled

together ie stone column-geocell mattress combined the bearing

capacity was increased by 102 fold Additionally visible reduction

in slope of pressure settlement responses indicates that the stone

column-geocell composite reinforcement can increase the stiffness

of the foundation bed signi1047297cantly leading to large scale reduction

in footing settlement

The load carrying capacity of the geocell-stone column rein-

forced foundation bed increases with increase in length of stone

columns until 5dsc beyond which further rate of improvement has

reduced down Similarly reducing the spacing of stone columns

below 25dsc does notattract much of additional performance in the

composite system Besides with height of geocells increasing

beyond 11D the performance improvement is found to have

reduced This is possibly due to the stress concentration induced

buckling and yielding of geocells right under the footing that the

increase in strength and stiffness of the system due to increase in

height of the mattress remains immobilised Hence it can be said

that the critical height of geocell mattress giving optimum per-

formance improvement in the composite foundation bed is equal

to about the diameter of the footing (D)

At times practical constraints may prevent in going for large

height geocell mattress or long stone columns severely compro-

mising the performance of the system In such situations the

geocell-stone column composite reinforcement provides an effec-

tive solution for adequate performance improvement and optimum

design of foundations on soft clay This is inferred from the present

study that a shallow height geocell mattress along with medium

length stone columns can provide comparable performance im-

provements as that with deep geocells or long stone columnsHowever full-scale testing and 1047297eld trails are required to verify

these observations

The 1047297ndings of the present study can be of use in the design and

construction of structures over soft clay deposits such as railways

highways foundations for liquid storage tanks large stabilised

areas for parking platforms for oil exploration etc The authors

have also conducted tests with basal geogrid underneath the geo-

cell mattress and the results shall be reported in a subsequent

paper

Acknowledgement

The authors are thankful to the anonymous reviewers for their

valuable comments and suggestions for improvements of the pre-

sentations in the paper

Notation

C c coef 1047297cient of curvature

C u coef 1047297cient of uniformity

D diameter of footing

dgc diameter of geocells

dsc diameter of stone column

emax maximum void ratio

emin minimum void ratio

h height of geocell mattress

g ethp1p2p3p4p13THORN frac14 g

s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)




IFsc bearing capacity improvement factor due to stone column

reinforcement

IFgc bearing capacity improvement factor due to geocell

reinforcement

IFgcsc bearing capacity improvement factor due to stone

column-geocell composite reinforcement

L length of stone column

qsc bearing pressure with stone column reinforcement

qgc bearing pressure with geocell reinforcement

qgcsc bearing pressure with stone column-geocell composite

reinforcement

r d deformed radius of stone column

r o original radius of stone column

S spacing of stone columns

s settlement of footing

u depth of placement of geocell mattress

References

Abdullah CH Edil TB 2007 Behaviour of geogrid-reinforced load transfer plat-forms for embankment on rammed aggregate piers Geosynth Int 14 (3) 141e153

Ambily AP Gandhi SR 2007 Behaviour of stone columns based on experimental

and FEM analysis J Geotech Geoenviron Eng ASCE 133 (4) 405e

515Arulrajah A Abdullah A Bouzza A 2009 Ground improvement technique for

railway embankments Ground Improv 162 (1) 3e14ASTM D2487 2006 Standard Practice for Classi1047297cation of Soils for Engineering

Purposes (Uni1047297ed Soil Classi1047297cation System) ASTM International West Con-shohocken PA httpdxdoiorg101520D2487-06E01

ASTM D4318 2005 Standard Test Methods for Liquid Limit Plastic Limit andPlasticity Index of Soils ASTM International West Conshohocken PA httpdxdoiorg101520D4318-05

ASTM D4884 2009 Standard Test Method for Strength of Strewn Thermally BondedSeams of Geotextiles ASTM International West Conshohocken PA httpdxdoiorg101520D4884e09

ASTM D6637 2001 Standard Test Methods for Determining Tensile Properties of Geogrid by Single or Multi-rib Tensile Methods ASTM International WestConshohocken PA httpdxdoiorg101520D6637e01R09

Black J Sivakumar V MeKinley JD 2007 Performance of clay samples reinforcedwith vertical granular columns Can Geotech J 44 (1) 89e95

Bowel JE 1988 Foundation Analysis and Design fourth ed McGraw-HillSingapore

Buckingham E 1914 On physically similar systems Phys Rev APS 4 345 e376Bush DI Jenner CG Bassett RH 1990 The design and construction of geocell

foundation mattresses supporting embankments over soft ground GeotextGeomembr 9 (1) 83e98

Carroll Jr RG Curtis VC 1990 Geogrid connections Geotext Geomembr 9 (4e6)515e530

Cimentada A Costa AD Izal JC Sagaseta C 2011 Laboratory study on radialconsolidation and deformation in clay reinforced with stone columns CanGeotech J 48 (1) 36e52

Christoulas S Bouckvalaas G Giannaros C 2000 An experimental study on themodel stone columns Soils Found 40 (6) 11e22

Chummer AV 1972 Bearing capacity theory from experimental results J SoilMech Found Div ASCE 98 (12) 1311e1324

Cowland JW Wong SCK 1993 Performance of a road embankment on soft claysupported on a geocell mattress foundation GeotextGeomembr12 (8) 687e705

Dash SK Bora MC 2013 2013 In1047298uence of geosynthetic encasement on theperformance of stone columns 1047298oating in soft clay Can Geotech J 50 (7) 754e

765Dash SK Krishnaswamy NR Rajagopal K 2001 Bearing capacity of strip footing

supported on geocell-reinforced sand Geotext Geomembr 19 (4) 235e256Dash SK Sireesh S Sitharam TG 2003a Model studies on circular footing

supported on geocell reinforced sand underlain by soft clay Geotext Geo-membr 21 (4) 197e219

Dash SK Sireesh S Sitharam TG 2003b Behaviour of geocell reinforced sandbeds under circular footing Ground Improv 7 (3) 111e115

Dash SK Rajagopal K Krishnaswamy NR 2004 Performance of different geo-synthetic reinforcement materials in sand foundations Geosynth Int 11 (1)35e42

Dash SK Rajagopal K Krishnaswamy NR 2007 Behaviour of geocell reinforcedsand beds under strip loading Can Geotech J 44 (7) 905e916

Dash SK Reddy PDT Raghukanth STG 2008 Subgrade modulus of geocell-reinforced sand foundations Ground Improv 12 (2) 79e87

Deb K Chandra S Basudhar PK 2007 Generalised model for geosynthetic-reinforced granular 1047297ll-soft soil with stone columns Int J Geomech ASCE 7(4) 266e276

Deb K Samadhiya NK Namdeo JB 2011 Laboratory model studies on unrein-forced and geogrid-reinforced sand bed over stone column-improved soft clayGeotext Geomembr 29 (2) 190e196

Fakher A Jones CJFP 1996 Discussion of bearing capacity of rectangular footingson geogrid reinforced sand by Yetimoglu T Wu JTH Saglamer AJ GeotechEng ASCE 122 (4) 326e327

Hughes JMO Withers NJ 1974 Reinforcing of soft cohesive soils with stonecolumns Ground Eng 7 (3) 42e49

Juran I Guermazi A 1988 Settlement response of soft soils reinforced by com-pacted sand columns J Geotech Eng ASCE 114 (8) 930

e942

Latha GM Somwanshi A 2009 Effect of reinforcement form on the bearing ca-pacity of square footings on sand Geotext Geomembr 27 (6) 409e422

Leshchinsky B Ling H 2013 Effects of geocell con1047297nement on strength anddeformation behaviour of gravel J Geotech Geoenviron Eng ASCE 139 (2)340e352

Madhavi GL Vidya SM 2007 Effects of reinforcement form on the behaviour of geosynthetic reinforced sand Geotext Geomembr 25 (1) 23e32

Malarvizhi Ilamparuthi 2007 Comparative study on the behaviour of encasedstone column and conventional stone column Soils Found 47 (5) 873e885

McKelvey D Sivakumar V Bell A Graham J 2004 Modeling vibrated Stonecolumns on soft clay Geotech Eng Proc Inst Civil Eng 157 (3) 137e149

Mayerhof GG Sastry VVRN 1978 Bearing capacity of piles in layered soils part2 Can Geotech J 15 (2) 183e189

Pinto MIM Cousens TW1999 Modelling a geotextile-reinforced brick-faced soilretaining wall Geosynth Int 6 (5) 417e447

Selig ET McKee KE 1961 Static and dynamic behaviour of small footings J Soil

Mech Found Div ASCE 87 (6) 29e

47Sireesh S Sitharam TG Dash SK 2009 Bearing capacity of circular footing ongeocell-sand mattress overlying clay bed with void Geotext Geomembr 27 (2)89e98

Tanyu BF Aydilek AH Lau AW Edil TB Benson CH 2013 Laboratory eval-uation of geocell-reinforced gravel subbase over poor subgrades Geosynth Int20 (2) 47e61

Webster SL Watkins JE 1977 Investigation of Construction Techniques forTactical Bridge Approach Roads across Soft Ground Technical Report S-77e1United States Army Corps of Engineers Waterways Experiment Station Mis-sissippi USA

Wood DM Hu W Nash DFT 2000 Group effects in stone column foundationsmodel tests Geotechnique 50 (6) 689e698

Zhou H Wen X 2008 Model studies on geogrid or geocell-reinforced sandcushion on soft soil Geotext Geomembr 26 (3) 231e238




piled raft system leading to improved load capacity However geo-

cell is a superior form of reinforcement over the planar one ( Dash

et al 2004 Madhavi and Vidya 2007 Latha and Somwanshi

2009) This is mostly due to its three dimensional con1047297ning struc-

ture that prevents lateral spreading of soil Therefore the sand

cushion over the stone columns if reinforced with geocells is ex-

pected to produce enhanced performance improvement These as-

pects are studied herein through a series of laboratory-scale model

tests The results have been analysed in developing an under-

standing of the behaviour of clay foundations reinforced with the

stone column-geocell mattress composite system

2 Details of model tests

21 Planning of experiments

Schematic sketch of a typical test con1047297guration is shown in

Fig 1 The stone columns were left 1047298oating in the clay bed This was

to simulate the situation commonly encountered in coastal areas

wherein soft clay deposits extend over very large depths that the

stone columns are generally terminated in the clay itself The col-

umns were placed in triangular pattern at a regular spacing S

(Fig 2) In all the tests diameter of stone columns (dsc) was kept

constant as 100 mm

Geocells were formed in chevron pattern (Fig 3) as it gives

better performance improvement over the diamond pattern (Dash

et al 2001) Diameter of geocells (dgc) taken as equivalent diam-

eter of geocell pocket opening was kept constant as 08D

throughout (D diameter of footing) The geocell mattresses were

placed at a constant depth (u) of 01D from the base of the footing

which was found to be the optimum location giving maximum

performance improvement (Dash et al 2008)

In total twelve series of model load tests were conducted the

details of which are presented in Table 1 Within each series onlyone parameter was varied This was to understand the in1047298uence of

this particular parameter on the overall behaviour of the founda-

tion system while the others were kept constant Tests in series 1

were performed on unreinforced clay beds Series 2 and 3 consisted

of testing the stone column reinforced clay beds wherein the in-

1047298uence of length (L) and spacing (S ) of the columns werestudied In

all these tests there was no sand cushion over the clay beds The

effect of height of geocell-sand mattress (h) was studied under

series 4 Subsequently tests in series 5e12 were designed to

LStone

column

Clay

Sand h

u

Geocell layer

DT DTDT DTDT DTDTDT

Footing

D D D

(00) xDxD

Fig 1 Schematic diagram of test con1047297guration

S

dsc

S

Stone column

Fig 2 Layout of stone columns

transverse member diagonal member

bodkin joint

b

b

Fig 3 Geocell system in chevron pattern plan view

Table 1

Details of model tests

Testseries

Typeof reinforcement

Details of parameters investigated

1 Un rei nforc ed cl ay bed wi th c u of 5 kPa

2 SC Variable parameter Ldsc frac14 1 3 5 7

Constant parameter S dsc frac14 25

3 SC Variable parameter S dsc frac14 15 25 35

Constant parameter Ldsc frac14 5

4 GC Variable parameter hD frac14 053 09 11 16

Constant parameter dgcD frac14 08 bD frac14 6


Constant parameter



Constant parameter



Constant parameter



Constant parameter



Constant parameter



Constant parameter



Constant parameter



Constant parameter


Note SC Stone columns GC Geocell-sand mattress






22 Materials used



























200 kPa was 44

23 Test setup































the tank walls
























0001 0010 0100 1000 10000 100000

Particle size (mm)

0

20

40

60

80

100

P e r c e n


stone aggregate

sand

clay


Fig 5 Test set-up



































2007)
















less than 15

25 Test procedure


















radius
















0

4

8

12

16

20

24

28


t s D

( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC








































sections
















Table 2




2 SC Ldsc frac14 1 169 125 114 119 123 126 128 130

SC Ldsc frac14 3 181 154 153 160 162 166 173 173

SC Ldsc frac14 5 359 287 293 312 319 331 340 344

SC Ldsc frac14 7 369 320 317 337 340 348 356 360

3 SC S dsc frac14 15 366 290 320 345 349 361 367 370

SC S dsc frac14 25 359 287 293 312 319 331 340 344

SC S dsc frac14 35 197 147 167 184 181 186 190 193

4 GC hD frac14 053 134 150 164 186 195 211 226 232

GC hD frac14 09 210 218 283 303 335 359 411 433

GC hD frac14 11 290 410 477 557 600 660 712 739

GC hD frac14 16 420 481 543 614 654 708 764 787

































IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)





































0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7



0 4 8 12 16 20 24 28


0

1

2

3

4

5


δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



1 hD frac14

053 S dsc frac14

25) e

Test series 5




















bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942




















22 Materials used



























200 kPa was 44

23 Test setup































the tank walls
























0001 0010 0100 1000 10000 100000

Particle size (mm)

0

20

40

60

80

100

P e r c e n


stone aggregate

sand

clay


Fig 5 Test set-up



































2007)
















less than 15

25 Test procedure


















radius
















0

4

8

12

16

20

24

28


t s D

( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC








































sections
















Table 2




2 SC Ldsc frac14 1 169 125 114 119 123 126 128 130

SC Ldsc frac14 3 181 154 153 160 162 166 173 173

SC Ldsc frac14 5 359 287 293 312 319 331 340 344

SC Ldsc frac14 7 369 320 317 337 340 348 356 360

3 SC S dsc frac14 15 366 290 320 345 349 361 367 370

SC S dsc frac14 25 359 287 293 312 319 331 340 344

SC S dsc frac14 35 197 147 167 184 181 186 190 193

4 GC hD frac14 053 134 150 164 186 195 211 226 232

GC hD frac14 09 210 218 283 303 335 359 411 433

GC hD frac14 11 290 410 477 557 600 660 712 739

GC hD frac14 16 420 481 543 614 654 708 764 787

































IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)





































0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7



0 4 8 12 16 20 24 28


0

1

2

3

4

5


δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



1 hD frac14

053 S dsc frac14

25) e

Test series 5




















bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942

















































2007)
















less than 15

25 Test procedure


















radius
















0

4

8

12

16

20

24

28


t s D

( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC








































sections
















Table 2




2 SC Ldsc frac14 1 169 125 114 119 123 126 128 130

SC Ldsc frac14 3 181 154 153 160 162 166 173 173

SC Ldsc frac14 5 359 287 293 312 319 331 340 344

SC Ldsc frac14 7 369 320 317 337 340 348 356 360

3 SC S dsc frac14 15 366 290 320 345 349 361 367 370

SC S dsc frac14 25 359 287 293 312 319 331 340 344

SC S dsc frac14 35 197 147 167 184 181 186 190 193

4 GC hD frac14 053 134 150 164 186 195 211 226 232

GC hD frac14 09 210 218 283 303 335 359 411 433

GC hD frac14 11 290 410 477 557 600 660 712 739

GC hD frac14 16 420 481 543 614 654 708 764 787

































IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)





































0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7



0 4 8 12 16 20 24 28


0

1

2

3

4

5


δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



1 hD frac14

053 S dsc frac14

25) e

Test series 5




















bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942
















































sections
















Table 2




2 SC Ldsc frac14 1 169 125 114 119 123 126 128 130

SC Ldsc frac14 3 181 154 153 160 162 166 173 173

SC Ldsc frac14 5 359 287 293 312 319 331 340 344

SC Ldsc frac14 7 369 320 317 337 340 348 356 360

3 SC S dsc frac14 15 366 290 320 345 349 361 367 370

SC S dsc frac14 25 359 287 293 312 319 331 340 344

SC S dsc frac14 35 197 147 167 184 181 186 190 193

4 GC hD frac14 053 134 150 164 186 195 211 226 232

GC hD frac14 09 210 218 283 303 335 359 411 433

GC hD frac14 11 290 410 477 557 600 660 712 739

GC hD frac14 16 420 481 543 614 654 708 764 787

































IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)





































0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7



0 4 8 12 16 20 24 28


0

1

2

3

4

5


δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



1 hD frac14

053 S dsc frac14

25) e

Test series 5




















bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942




















IFgcsc

IFscfrac14

qgcsc

qu

qsc

qu

frac14 qgcsc

qsc(1)





































0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

1

2

3

4

5


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



053 S dsc frac14

25) e

Test series 5

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7



0 4 8 12 16 20 24 28


0

1

2

3

4

5


δ D ( )

Clay

Clay+GC

Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



1 hD frac14

053 S dsc frac14

25) e

Test series 5




















bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942


































bulged


















































0

4

8

12

16

20

24

28


n t s D ( )

0 20 40 60 80 100 120 140 160


Clay

Clay+GC






0 4 8 12 16 20 24 28


0

1

2

3

4








0 4 8 12 16 20 24 28


0

1

2

3

4







09 Ldsc frac14

5) e

Test series 10











































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942

























































observation










4 Scale effect








0 4 8 12 16 20 24 28


00

05

10

15

20

25

30



Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



0 4 8 12 16 20 24 28


0

2

4

6

8

10


Clay+GC+SC(Ldsc= 1)

Clay+GC+SC(Ldsc= 3)

Clay+GC+SC(Ldsc= 5)

Clay+GC+SC(Ldsc= 7)



16 S dsc frac14

25) e

Test series 8

0

1

2

3

4

5

6

7


0 5 10 15 20 25 30


Ldsc= 1

Ldsc= 3

Ldsc= 5

Ldsc= 7












f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942
























f


frac14 0 (2)






model (m)

Dp

Dmfrac14 n (4)



Gp

Dpgpfrac14

Gm

Dmgm(5)



reduces to

Gp

Gmfrac14 Dp

Dmfrac14 n (6)


K pgp

G2p

frac14 K mgm

G2m

K p

G2p

frac14 K mG2

m

K pK m

frac14G2

p

G2m

frac14 n2 (7)









5 Conclusions








































these observations







paper

Acknowledgement




Notation










s

D

h

D

dgc

D

h

dgc

dsc

D

L

D

S

D

d50

dsc

G

Dg

K g

G2

c uDg

qgcsc

qu

f

frac14 0 (3)





reinforcement


reinforcement







reinforcement






References
































e942



















reinforcement


reinforcement







reinforcement






References
































e942
















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