effect of different modulus elasticity of geotextile encasing the stone column to the strength of...

8/9/2019 Effect of different modulus elasticity of geotextile encasing the stone column to the strength of improved soil

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CHAPTER 1

INTRODUCTION

1.1 Introduction

Many failures of buildings are causes by instability of the soil. Usually engineers focused on the

quality of material and less focused on the condition of soil. There are three types of soil, soft

soil, medium soil and hard soil. Soft soil is the most dangerous in term of safety compared with

the other type of soil as it has low bearing capacity and tends to settle frequently. Soft soil can be

found near a river, ocean, soil above the underground water and many more. There are many

techniques which can strengthen and reduce the settlement of the soil; one of it is stone column

technique.

Commonly many construction companies choose stone column as soil improvement

method which can increase the geotechnical properties of soil stabilie road emban!ment or

structures on soft soil "#saac and $irish, %&&'(. The diameter of stone column usually is between

&.) to *.% m and their intervals between *.+ to ) m. The stone column can reduce the settlement

of the surrounding soil as it absorb the load from the soil so that the bearing capacity of soil is

increase which in turn reduce deformation of soil. The interaction between the soil and stone

column can be investigated by predicting the soil settlement that will occurred in a specified

time. Usually prediction of soil settlement is done by using %d finite element analysis. y using

this method the behavior of deformed stone column can be fully investigated and understand.

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-aresh and Sandip"%&*%(stated that some of the advantages of incorporating stone column

into the soil that is improve slope stability, increase bearing capacity of shallow foundation,

reduce settlement of soil, and decreasing the potential of sandy soils to liquefaction. -aresh and

Sandip"%&*%( also added that the performance of stone columns for reinforced and improved soil is

easier and cheaper than other methods such as geotetile, grouting, and compaction. Many

construction companies choose stone column as improvement method as it is cheaper and easy to

install as today cost of construction is one of ma/or factor in construction industry. Many

contractors want to reduce cost as low as possible in order to gain profit but at the same time

ensure that the end product is safe for people to live and use. Stone column can be installed

without casing or with casing. Column that is encasing by geoteile can improve the

performance of stone column in improving the soil. Tandel 0. 1. et al. "%&*%( founded that when

the column is encapsulated; it can prevent stone at the column from clattering into surrounding

soil and can stiffen the stone column. Material uses for encasing the stone column are

polypropylene, polyester, etc.

#n order to simulate the behavior of soil without doing and eperiment, we can choose to

use engineering based software. There are lots of geotechnical software created by the software

engineer to help engineers smoothen their wor!s and speed up the design process of buildings

and foundation. 2ne of the geotechnical software that are commonly use worldwide is -345#S.

-345#S is a simulation software use in geotechnical department that simulate the behavior of

clay using finite element method. There are two type of -345#S software, one was -345#S %d

and another one is -345#S )d, with each type of -345#S had its own advantages and different

offers to the end users. -345#S are frequently updated and latest version are the most up to

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dated and bug free to ensure that there are no errors to the result produce by the software and to

ma!e the result as accurate as possible.

-345#S 6 or -345#S %d is widely use by most geotechnical engineer due to its ability to

simulate the behavior of soil accurately. -345#S had being use in determining slope of soil,

analyse pile settlement in soil, simulate structural layer of soil for earthqua!e analysis and its

impact to the building structure, and many more. -345#S can be used for the analysis of

deformation and stability in geotechnical engineering. The improved Soil is modeled with *+

nodes triangular finite elements "4minaton et al., %&*)(.

Most of the stone column reinforced foundation analyses were carried out either in

aisymmetric unit cell or two7dimensional full7scale emban!ment system. -345#S can be used

to determine behavior of stone column in soft clay for eample the settlement of the soil

improved by the stone column. Usually analysis using -345#S is use to verified or compare the

result obtained from the software and result obtain from the eperiment conducted in lab.

1.2 Problem Statement

The focus of this study is to investigate performance of stone column encapsulated by geotetile

in improving the soil. Studies of the performance of encapsulated stone clone involve with

eamining the various behavior of geoteile that encapsulated the stone column under different

set of modulus. 8ifference in modulus of the geoteile is said to have impact at the performance

of stone column in improving the soil properties such as bearing capacity and soil settlement.

Malarvihi and #lamparuthi "%&*&( stated that casing the stone column with geotetile can give

positive impact to stone column such as for eample increase the stiffness of the stone column,

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improve strength of the stone column and prohibited the horiontal movement of the stone

column which in return reduce time allocated to install the stone column while maintaining the

quality of stone column such as drainage and frictional properties.

9inding the suitable engineering software related to geotechnical engineering is a very

hard tas!. 4lthough up until today there are about : to + software being offer out there. The most

outstanding among those of the software is S4$ Chile laboratory or in situ eperiment has no limitation issue, software on the other

hand had limitation over certain etent 2ng et al. "%&&?( found that regarding to the depth or

scale of the model, in order to prevent or avoid interfering of lower boundaries of the mesh with

the solution of area of interest. Thus although software offer abundance of advantage such as

speed up the analysis of the soil, free of human error or paralla error eperiment and analysis,

can simulate soil interaction without having a real model, etc. is still has a limitation to what it

can perform so overusing the software outside its capacity can lead to dead end.

#n order to observe the settlement behavior of the soft soil with stone column as a ground

improvement method encased with geotetile, we use %78 finite element to analyses the

aisymmetric unit model cell. )78 model finite element analysis is very time consuming so in

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order to save time %78 method were preferred. Scale of the model represented the actual soil

scale. The diameter of the column and model are !ept in constant throughout the analysis with

specific properties of the model are specified. To ensure there will be no horiontal movement of

the soil, each horiontal side of the %78 finite element model is restricted. ach of these models

such as soil, plate is set to with specified parameters that are !ept constant. 2nly geotetile

properties are being change for at least : times with different value of modulus. Changing the

modulus of the geotetile is done in purpose of producing a graph showing relation of different

parameters such as settlement versus time, cess pore pressure versus time, effective stress

versus time, and effective stress versus settlement.

1.3 Obecti!e o" #tud$

Stone column are the most efficient ground improvement method among the other methods

available. Many ma/or geotechnical engineering local and international practice the uses of stone

column to improve the soft soil on the construction site. 9rom years to years the popularity of

stone column is rising. 8ue to innovative idea of the engineer, new type of stone column !nown

as encased stone column which is a stone column encased by the geotetile. ncased stone

column are still not widely use and un!nown by most engineering company.

So the ob/ective of the study is to analye the effect of geotetile column to the soil as the

new type of stone column. The aim of the study is to eplore more deeply about this new type of

stone column and analye the behavior of it with the soil. Settlement, pore pressure, etc. are the

criteria which are the essential factors of determining efficiency of the encased stone column.

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Second ob/ective is that this studies aim to build the relationship between the parameters of soil

so that when the relationship are produce, we can observe what degree of impact can encased

stone column can offer. The ob/ectives of this research are specifically stated below@

#. To determine effective vertical stress of composite encased stone column with various

modulus of geotetile along primary consolidation using -345#S.##. To determine the settlement of composite encased stone column along primary

consolidation using -345#S.###. To determine ecess pore pressure of surrounding soil along primary consolidation

using -345#S.#A. To relate effective vertical stress with vertical displacement along primary

consolidation using -345#S.A. To determine hoop force surrounding stone column along primary consolidation using

-345#S.

1.% Sco&e o" #tud$

The study is performed by analying the behavior of encased stone column using -345#S. The

study is focused only for encased stone column that is use as ground improvement method.

Stone column are made from only one material that is aggregates, but other material such as

quarry sand, gravel, etc. can be used as alternative to aggregates. Stone column has a cylindrical

shaped with certain diameter and depth. #n this research mohr7coulomb model had being used.

The sie of the model is &.&)+ meter in depth and &.*+ meter in diameter. 4 uniform load are

applied throughout the whole diameter of the model and evenly distributed with no difference in

intensity of loading. 4 rigid plate is applied at the top of the model. The soil material used in this

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research is considered to have an undrained condition while stone column material is consider

drained condition.

ehavior of various modulus of geotetile of encased stone column is simulated by using

a finite element software call -345#S %d. -345#S version 6.% is used and this version can only

do analying in %78 finite element only, so )78 finite element is not involved at all. 4s %78 9M

are more time saving and friendly user than )78 9M, is give more advantage using %78 than )7

8. The model that will be analye by -345#S will consist of one encased tone column with

geotetile layer having various stiffness value, one type of soil, one plate and uniform load

displacement on the top of the soil and plate. -late is applied to the whole diameter of the model.

To ma!e this studies more specified, the studies is focused on analysis of stone column

with different modulus of geoteile. So geoteile is be included in the %78 finite element model.

-345#S had an option to include geoteile to the model which ma!e the tas! to analye the

9M model easier and user friendly. 4s to analye the geoteile of different modulus, different

values of modulus is be used starting from the lower value and increment in a fied value until +

results with different modulus of geoteile is achieved.

1.' (imitation o" #tud$

B


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This study focused on the effectiveness of the encased stone column as a method of soil

improvement based on factors such as settlement, pore pressure, etc. This studies only limited to

an aisymmetry finite element model of *+ triangular node element of encased stone column

and one type of soil as the primary target for this studies is to measure the impact of geoteile

encasing the stone column so only geotetile properties will be varied throughout the simulation.

The only property of geotetile which is being change is the modulus of geotetile. The modulus

value of geotetile that is used in this research is %&&, :&&, ?&&, 6&& and *&&& !Dm.

Throughout the studies, only -345#S had being used as simulation software to simulate

the interaction of soil using finite element method. 4lthough there are many geotechnical

engineering based software around the world for eample S4$7C


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1.) Si*ni"icant o" #tud$

This study is significant to the geotechnical engineering department and contractor. This

studies can verified the impact that geotetile can have to the stone column. The impact can be

good or can be bad. #f the impact is good and positive, geotechnical engineers will more li!ely to

incorporate the encased stone column rather than the ordinary stone column into the soil. #f the

impact is not very good or bad or doesn=t have an effect at all, then the used encased stone

column can be neglected and use the ordinary stone column. The capability of stone column to

improve the soil surrounding it can be observed more deeply as there is still lac! of studies about

it. >ith this research, geotechnical engineers can predict how big the settlement can be reduced

when incorporating the stone column into the soil. 9urthermore contractor can be ensure that

stone column are the cost cut method of improving the soil compare to other possible method

available. The capability of -345#S to simulate the soil and column can be test and eplore

more deeply as the use of -345#S are still new and not widely epose to many engineering

department especially in Malaysia.

CHAPTER 2

(ITERATURE RE+IE,

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2.1 -eneral conce&t o" #tone column

The term EStone ColumnF clearly defined the material and shape of the stone column. The only

material need to form a stone column is aggregates. The aggregates are being compacted into a

collective group of stone in a shape of cylinder. Most of us commonly mista!en by assuming that

stone column is same as concrete column. 4lthough they share similarities for eample their

shape and material, there are a difference which ma!es them distinctive from each other. The

difference between stone column and concrete column is that stone column does not mi with

cement as binding agent, but using compaction to reduce gaps between the individual aggregates

while the surrounding soil !ept the aggregates in shape. 9or concrete column the aggregates had

to being mi with cement and water to bind the aggregates together and had to be dried for the

column to achieve the optimum strength and ready to be use on site. 8ifference between stone

column and concrete column are shown in Table %.*

Table 2.1 8ifference between stone column and concrete column.

Stone Column Concrete Column

*. The only material use to form the

column is aggregates.

*. Use aggregates, cement and water mi

in a certain ratio.

%. Cast in7situDon7site %. Can be cast on7site or precast before

transfer on site for use.

). 8oes not need to wait %B days to

achieve optimum strength, can be used

straight away.

). eed to wait for %B days for the

concrete mi to achieve optimum

concrete strength.

2.1.1 Stone column a# *round im&ro!ement met/od.

*&


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Stone column is one of the method that can is used widely to improve the soil condition

around the site. ample of ground improvement methods that can be used other than stone

column is dynamic compaction, /et grouting, soil miing, cement stabiliation, etc. These lists of

ground improvement provide the geotechnical engineer many options to choose depending on

the type of soil and needs. Criteria for selection of ground improvement based on factors for

eample cost, time, difficulty, facilities, labors, !nowledge and many more.

Usually time and cost are the primary factors that decide which method is used as this

two criteria effect the cost of construction and time of completion of the construction. Commonly

geotechnical engineer choose stone column as ground improvement methods. The advantage of

stone column compare to all the other methods is that it is easy to install, cheaper cost as it use

cheap material such as aggregates, shorter time to install and prepare for use on site, not comple

installation compare to other methods, etc.4ll the ground improvement method are used to wor! with eisting ground ecept for

rigid inclusion li!e piles which are intend to bypass the ground to a certain degree. Stone column

load transfer mechanism is shown at 9igure %.*. McCabe et al. "%&&B( in his research eplained

that the load is transmitted by interaction of column7soil interface or in other name shear stress

and end bearing.

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0i*ure 2.1 (oad tran#"er reaction o" a &ile and b #tone column cCabe et al.4

2556.

Soil has many properties which define its behavior and the way it react when load is applied to it.

The most common properties that are used to determined the quality and type of soil is

settlement and bearing capacity. The stone column is functioning by improving ground

characteristics such as reduce settlement and increasing bearing capacity of surrounded soil, and

ease the drainage system by transferring the drainage path from vertical to horiontal. The soil

displacement is occurring laterally or horiontally while the installation process occurred@

7 $eneration of ecess water pressure is occurred and is assumed to scatter around the permeable

columns;

7 #ncreased in horiontal stresses, which in result caused the coefficient of earth pressure 1 to

eceed the original rest coefficient, 1o.

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2.1.1.1 7earin* Ca&acit$

earing capacity is an ability of the soil itself to withstand applied load on it. The load can be in

form of line load, point load, circular load, continuous load, rectangular load, etc. Ultimate

vertical stress "q( in a stone column could be predicted by using the equation below;

qG1+sin

1sin " r o

'+4c

where H= is the stone friction angle , IJro is the free7field lateral effective stress and c is the

undrained strength. This equation had being used around the world and is widely practiced by

professional engineer, students, lecturers, etc.


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the stone column diameter can have great impact to the bearing capacity value of the soil, so

deeper research still needed to validate it.

2.1.1.2 Settlement

8efinition settlement of soil is reduce of soil volume by applied eternal load which

result in reducing water content of the soil without substitution by air. #saac and $irish "%&&'(

had conducted and eperiment about the effect of number of column installed in the soil to the

settlement of the soil. #t is found using group of three columns can improve the load deformation

parameter and if using group of seven columns it will improve better than ) columns.

9urthermore #saac and $irish "%&&'( also found that spacing between stone columns can also

have an impact. 3oad capacity, can be improved by reducing the spacing between the stone

column and if the spacing is increased, the load capacity is decreased. 9igure %.%, 9igure %.),

9igure %.:, 9igure %.+, 9igure %.? shows the result of the eperiment conducted by #saac and

$irish "%&&'(. The number of column and spacing between columns is varied to get different

result and compared the different of the result.

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0i*ure 2.2 (oad !# #ettlement *ra&/ "or #in*le #tone column I#aac and -iri#/ .S.4 2558.

0i*ure 2.3 (oad !# #ettlement *ra&/ "or 6 column S&acin*93d I#aac and -iri#/ .S.4

2558.

*+


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0i*ure 2.% (oad !# #ettlement *ra&/ "or 6 column S&acin*92.'d I#aac and -iri#/ .S.4

2558.

0i*ure 2.' (oad !# #ettlement *ra&/ "or 3 column S&acin*93d I#aac and -iri#/ .S.4

2558.

*?


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0i*ure 2.) (oad !# #ettlement *ra&/ "or 3 column S&acin*92.'d I#aac and -iri#/ .S.4

2558.

2.1.2+ibro 0loatation a# a met/od o" ordinar$ #tone column in#tallation.

McCabe et al. "%&&B( stated that vibro floatation method is a general definition of method for

installing ordinary stone column into the ground as the mean of improving soil condition by

penetrating the ground using vibrating po!er and the process involve vibro7replacement and

vibro7compaction. 9urthermore McCabe et al. "%&&B( also added that there are two common

ways which the stone can be inserted into the ground which is top feed and bottom feed. The

vibrating po!er is inserted into the ground by the mean of penetration and vibration to create the

hole inside the soil which will be the place where the stone will be filled in to form a stone

column. Then after the hole is created, the po!er is pulled out from the ground completely so

that stone can be put into the ground filling the hole created completely by using control volume.

*B


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That is for top feed system, but for bottom feed system there is a different approach in the ways

the stone is inserted. 9or bottom feed, it use rigged mounted hopper to insert the stone column

into the ground by using a tube. The inserting process of stone is done without pulling the po!er

out unli!e the stone system feed. 9igure %.B and 9igure %.6 will show the process of installing

stone column using top system feed and bottom system feed.

0i*ure 2.6 Proce## o" !ibro "lotation u#in* to& "eed #$#tem

*6

The hole is prepared by

penetrating the soil using

vibrofot. The hole is wash while

enetration o soil occurred.

When the insertation process o

stone occurred, water and air will

be push out o the hole.

During insertation o stone, vibrofot

will compact the stone by moving up

and down so that lateral compressionoccurred at the nearby soil. Stone

column is able withstand higher axial

load.


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0i*ure 2.: Proce## o" !ibro "lotation u#in* bottom "eed #$#tem.

Top feed system is suitable for the ground which when the hole is created, the hole will not

disclosed by the soil itself, means that silt and gravel soil is not suitable. 9or bottom feed system

it is more suitable to sandy and silt clay or soil with high ground water table.

2.1.3 Pa#t re#earc/ about ordinar$ #tone column.

There are numbers of etensive research conducts by many researchers in investigating

the effect of ordinary stone column in improving the ground condition.


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0i*ure 2.8 T;o di""erent condition# "or t/e e


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0i*ure 2.15 (oad !# #ettlement *ra&/ "or column area loaded Ambil$ and -and/i4 255%.

0i*ure 2.11 (oad !# #ettlement *ra&/ "or ;/ole area loaded Ambil$ and -and/i4 255%.

%*


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8ue to bulging of the stone column, failure can be seeing at 9igure %.**. 9rom the eperiment, it

can be conclude that higher shear strength can carry higher load and resulting lower vertical

displacement of soil.

8as and -al "%&*)( recently were investigating the impact of ordinary stone column to the soft

clay. Ke use two type of soil for this eperiment, one is sandy silt clay and the other one is silt

clay. The properties of the material use by 8as and -al "%&*)( the eperiment is shown in Table

%.) and Table %.:.

Table 2.3-roperties of aggregate "8as and -al, %&*)(.

-roperties of 4ggregate

Specific gravity %.?*)

>ater absorption %.:*B

4ngularity number :.%)

Shear strength C G '.6? !DmL

G :?.':

%%


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Table 2.%-roperties of soils "8as and -al, %&*)(.

Soil properties Sandy silt with clay Silty clay soil

P/$#ical &ro&ertie#

Sand "( )B.%' *B.%*

Silt content "( )).& +&.%+Clay content "( %'.B* )%.+:

Specific gravity %.?& %.+?

3iquid limit "( )&.*& )'.+&

-lastic limit "( *?.:? %&.+B

-lasticity inde "( *).?: *6.')

En*ineerin* &ro&ertie#

2ptimum moisture content

"(

*B.*& *6.+&

Maimum dry density

"!DmN(

*B.%? *?.BB

4ngle of friction, "in

degree(

%:.&& *'.)B

Cohesion, c "!DmL( *).B' *+.&:

The result of the eperiment is produce in load versus settlement graph. 8as and -al "%&*)( from

his research found that by increasing diameter of ordinary stone column, the soil bearing

capacity for the sandy silt with clay increase and thus improve the soil performance. 9igure %.*%

shown the load settlement behavior for sandy silt with clay soil.

%)


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0i*ure 2.12 (oad #ettlement *ra&/ "or ordinar$ #tone column rein"orced #and$ #ilt cla$ #oil

Da# and Pal4 2513.

8as and -al "%&*)( in his research had also investigated the effect of ordinary stone column to

layer soil which consists of silt clay at the top layer and sandy silt clay at the bottom layer. Ke

had found that increased in diameter of stone column cause decreasing of performance of the soil

in term of bearing capacity. The cause for this undesired impact is due to bulging of stone

column resulting from poor confines pressure offered by top layer of soil which is silt clay.

2.1.3.1 Stone u#ed a# material# "or #tone column com&ared ;it/ ot/er material#.

Stones had being used as a main material for stone column by many geotechnical engineering

worldwide due to its performance when compared with other materials. 3ist of materials that can

be used for stone column besides stone is quarry dust, sea sand, river sand, gravel, etc. #saac and

$irish "%&&'( had conducted an eperiment to find which material is the best among the best.

%:


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9ive material, quarry dust, sea sand, river sand, gravel, and stone had being label m*, m%, m),

m:, and m+ respectively with each of them being use as material for stone column. 9igure %.*)

shows the result of the eperiment.

0i*ure 2.13 (oad de"ormation *ra&/ "or di""erent material o" #tone column"I#aac and

-iri#/4 2558.

The load deformation curve for stone is higher than the rest of material which shows that stone is

the best material for stone column. >hen using stone as stone column material, it will needs high

loading applied to it for the soil to settle and deform. Ouarry dust are the lowest quality of

material compare to the rest as the curve of the graph for it is lower which means that with small

applied load the soil will settle and deform easily.

2.2 Enca#ed Stone Column.

%+


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ncased stone column is same with ordinary stone column ecept with one different, encased

stone column are coat or being enclosed by a casing. The casing that are commonly use in today

practice is geotetile.


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column will be located. 4fter drilling, casing will be put into the soil. cess soil inside the

casing is removed before the introduction of stone. 4fter removing the remaining soil, the casing

is filled with stone and compacted layer by layer by using a rammer. Then the net step is to

introduce geotetile encasement into the casing and introduce stone column into the encasement

by using a hopper so that the stone is evenly filled and compacted until the column height reach

the surface of the ground

2.2.2 Re#earc/ about enca#ed #tone column.

4minaton et al. "%&*)( had conducted an eperiment to observe the impact reinforced

geotetile to the stone column. #n the eperiment, diameter of the column is varied and both

stone columns without geotetile and with geotetile are tested. 9igure %.*+ and figure %.*?

show the result of the eperiment.

%B


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0i*ure 2.1' -ra&/ o" #ettlement !er#u# load "or non rein"orced #tone column "Aminaton etal.4 2513.

0i*ure 2.1) -ra&/ o" #ettlement !# load "or rein"orced #tone column Aminaton et al.4

2513.

9rom the result we can see that encased stone column improve its strength by three times margin

better than non encased stone column. The clear result is tabulated in the Table %.+ below which

shows the clear difference of bearing capacity achieve by encased and non7encased stone

column.

Table 2.' earing capacity of stone column "4minaton et al., %&*)(.

Stone Column D935 D9%5 D9)5

7earin* Ca&acit$ in 25 mm #ettlement 'B.): *??.:B )+).66

Rein"orced Stone Column D935 D9%5 D9)5

7earin* Ca&acit$ in 25 mm #ettlement B).%: :B6.*+ B?%.B6

This show that encased stone column can be a better choice than ordinary stone column but a

better research is needed in order to eplore more deeply about the impact of geotetile

reinforcement for stone column. So that is why this paper is intent to produce more graph which

%6


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shows various relationship between different parameters such as ecess pore pressure, stress7

settlement, etc.

Malarvihi and #lamparuthi "%&*&( had conducted an eperiment which the ob/ective is to

find the factor that caused improvement to the behavior of the stone column when encase it with

geotetile casing so it means that the eperiment will show the interaction between stone

column, geoteile casing and the soil itself. The finite element model used by Malarvihi and

#lamparuthi "%&*&( is aisymmetry model of *+ node triangular element. The model consists of

clay, stone column and geotetile casing. 3oad is applied at the column area and etending to

certain area of clay. The analysis is carried by varying the diameter of the model and settlement

and determines the effect of variety of those two parameters to the bulging of the stone column.

The analysis is carried with one stone column without geotetile reinforcement and another one

with geotetile reinforcement.


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0i*ure 2.1: Radial #ettlement "or *eote


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stone column is due to the stiffness of the geotetile casing, the higher the value of stiffness, the

lower the strain produce which in turn lower the possibility to bulge.

4minaton et al. "%&*)( had also investigated the effect of various stiffness of geotetile to

compare the settlement of soil between reinforced stone columns with different value of

modulus. The diameter of the stone column is !ept constant which the value is ?&mm while the

value of stiffness of the geotetile encasing the stone column is varied starting from +& !Dm,

%+& !Dm, +&& !Dm, and *&&& !Dm. The result of the eperiment is shown below by Table %.?

and 9igure %.%&.

Table 2.)earing capacity of SC for various geogrid stiffness "4minaton et al., %&*)(.

Stone Column 2SC PG+& PG%+& PG+&& PG*&&&

earing

capacity

)+).' B?%.B6 6++.:B 6':.B* '%).B:

0i*ure 2.25 -ra&/ o" load de"ormation o" enca#ed #tone column ;it/ !ariou# !alue o"

#ti""ne## Aminaton et al.4 2513.

)*


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2nly load deformation graph are produced for 4minaton et al. "%&*)( eperiment, so

geogrid encased stone column needs more research and this shows the significant of this research

paper as it will unloc! !ey to understand mechanism of geogrid encased stone column. 2ther

than research by 4minaton et al. "%&*)(, Malarvihi and #lamparuthi "%&&6( in his research paper

had conducted an eperiment which use triaial test on encapsulated stone column to understand

the behavior of encapsulated stone column. The eperiment is analyed by using finite element

software called -345#S and also at the same time the eperiment is conducted in laboratory.

The result is plot in the graph and can be seen in the 9igure %.%* below. #t shows both result

from the eperiment and from software are compile in the same graph. The mesh model of

geogrid encased stone column can be seen at the 9igure %.%%. The model is an aisymmetric

model with the model generate with *+ node triangular elements. The model also is set to not

having horiontal movement from the left.

0i*ure 2.21 S/ear #tre## !er#u# #train relation#/i& &roduced b$ bot/ eIS alar!i=/i and Ilam&arut/i4 255:.

)%


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0i*ure 2.22 Simulation model to be anal$#e u#in* P(A>IS alar!i=/i and Ilam&arut/i4

255:.

The result from the eperiment conduct by Malarvihi and #lamparuthi "%&&6( found that

value of cohesion is increased as diameter of geogrid stone column is decrease and vice versa

and this means that the smaller column is much stiffer and produce more strength than higher

diameter of column.

Castro et al. "%&*)( recently were conducting a research for encasement stone column to

investigate effect of different stiffness of geotetile to the performance of settlement reduction to

the soil. The research is done by using -345#S as an analytical approach to investigate the

behavior of geotetile encasement and the model he is is shown in the 9igure %.%) below. 9rom

his research he found that increase in stiffness of geotetile can reduce the settlement of soil

around the encased stone column. Castro et al. state higher stiffness of geotetile can provide

more confinement to stone column thus increase the load capacity of the stone column. The

settlement7time graph from the research by Castro et al. is shown in 9igure %.%:.

))


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0i*ure 2.23 T/e te#t model. Ca#tro et al.4 2513.

0i*ure 2.2% Settlement?time *ra&/ Ca#tro et al.4 2513.

Castro et al. also found that by applying the geotetile as an encasement for stone column at the

top part of the column, it will reduce the strain of the stone column greatly as strain occurred

more greatly at the upper part of the column. This is shown at 9igure %.%+ as the deeper the depth

):


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of the column, the lower the strain of the stone column. The lower the strain at the stone column

the lower the tendency for the column to bulge so that the performance of the stone column in

improving the soil can be maintains.

0i*ure 2.2' De&t/?#train cur!e. Ca#tro et. al.4 2513.

0i*ure 2.2) Settlement?load cur!e. Ca#tro et al.4 2513.

)+


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9igure %.%? show the load bearing capacity relationship which Castro et al. "%&*)( conclude that

bearing capacity of the encased stone column increase with higher stiffness modulus of

geotetile.

Tandel et al. "%&*%( has recently conducted a numerical study of encased stone column.

Ke used -345#S to study the behavior of encased stone column in soil emban!ment. The %d

model of his research is shown in 9igure %.%B. 9rom his research, he found that by increasing the

stiffness of geotetile the load carrying capacity of reinforced stone column increase thus result

in lower settlement of the soil which can be seen at 9igure %.%6 below. Tandel et al. "%&*%( also

varying the modulus of soil which he conclude that increase in modulus of soil also resulting in

reducing of soil settlement.

0i*ure 2.26 T/e 2d model u#e b$ Tandel et. al 2512.

)?


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0i*ure 2.2: Settlement?time *ra&/ Tandel et al.4 2512.

Kataf and abipour "%&*)( recently had conducted a research to investigate effect of geotetile

reinforced stone column to the bearing capacity of the improved soil. #n his research, he used

different length of reinforcement to see whether it will improve the performance of encased stone

column. #n his research the cylinder sie for the test model is about *m in height and *m in

diameter. The cylinder is filled with soil with encased stone column at the centre of the cylinder.

The test model for the eperiment and material properties are shown in 9igure %.%' and Table %.B

below.

0i*ure 2.28 Te#t model "rom e


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Table 2.6-roperties of material use by Kataf and abipour "%&*)(.

-arameter Clay Sand

9riction 4ngle %? )+

Cohesion "!DmL( +.& &.&

Unit weight "!DmN( *+.& *?.&3iquid 3imit "( ::.+ 7

-lasticity #nde "( %&.& 7

9rom this eperiment, bearing capacity graph for all different length of encasement casing the

stone column are produced and analyed. Kataf and abipour "%&*)( found that by encasing the

stone column by half of the column length, it gives a similar performance with full length

encased stone column especially at clay type of soil thus give more benefits such as cost

reduction and material saving. lloue and ouassidan "%&&'( conducted a research which is to

investigate behaviour of soft soil by installing a group of stone column rather than single stone

column. lloue and ouassidan "%&&'( conducted a research which is more macroscopic and

covered the interaction between the stone columns in a formed of group. This research is more

microscopic and investigates deeply the interaction of single stone column which had being

encased by geotetile.

2.2.3 Ot/er re#earc/ about -eote


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$eotetile, other than use as an encasement or reinforcement for the stone column with

the means to improve strength and properties of stone column, it also can be used without stone

column to improve the properties of the soil layer and use as a reinforcement. Sivaoshnia et al.

"%&*&( had conduct and eperiment to investigate the effect of geotetile reinforced emban!ment

on the soil which the type of soil is soft clay. Ke stated that geotetetile or geosynthetics can be

use in wide range of engineering application such as separation, filtration, sealing, drainage and

reinforcement. Ke uses -345#S to assess the impact of having geotetile reinforced in the soil

and compare if the soil with no reinforced geotetile performed worst or better than reinforced

soil. The eperiment simulate ) emban!ment model, one of the model contain no geotetile

reinforcement, another one contain geotetile reinforcement at the lower layer of emban!ment

and the last one contain ) geotetile layer at each layer having one geotetile reinforcement.

9igure %.)&, 9igure %.)* and 9igure %.)% show the model emban!ment use by Sivaoshnia et al.

"%&*&(.

0i*ure 2.35 Emban@ment ;it/out *eote


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0i*ure 2.31 Emban@ment ;it/ one *eote


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Table 2.:Koriontal and vertical displacement with different number of geotetile "Sivaoshnia

et al., %&*&(.

o. of geotetile layer Koriontal displacement"cm( Aertical displacement"cm(

o geotetile layer )B 6+.+B2ne layer of geotetile layer %+.+' BB.6*

Three layer of geotetile layer %:.** B?.:+

9rom the result of the eperiment Sivaoshnia et al. "%&*&( conclude three things, first geotetile

layer can reduce about )& percent amount of horiontal settlement occurred near emban!ment

toe, secondly the higher the stiffness value of geotetile, the lower the displacement, and thirdly

by increasing number of geotetile layer, it will cause *.: percent of reduction for vertical

displacement and : percent for horiontal displacement.

2.2.% E


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#n geotechnical engineering there is about many software available which the

geotechnical engineer can do to simplified tas! or remove burden of wor! from them. 3ist of

standout software are $eo 9M, -345#S, Q7Soil, and S4$7C


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ntire area Column alone

% %+ )& 0es 0es

% )& *% 0es 0es

% )+ ?.+ 0es 0es

) )& *% 0es 0es

: )& *% 0es 0es

0i*ure 2.33 Te#t model u#e in t/e laborator$ e


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0i*ure 2.3% A


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both result from -345#S and eperiment are produced in the same graph to show clearly the

difference between both results.

0i*ure 2.3) (oad !# #ettlement *ra&/ ;it/ di""erent #d ratio# Ambil$ and -and/i4 255%.

>e can clearly seeing that the result produced by both eperiment and -345#S are about similar

to each other although it seems to have a gap of difference between them but the gap can be

ignored and still at an acceptable level. 4mbily and $andhi "%&&:( had conclude from his

eperiment the result produce by both eperiment and -345#S are very well compared and

analysed and from this result it can be a guide stone to decide whether it is safe to use -345#S

to simulate the behaviour of stone column without verify the result obtain by laboratory

eperiment.

Malarvihi and #lamparuthi "%&&6( had also conducted an eperiment which consist both

result from laboratory eperiment and -345#S. The laboratory eperiment is conducted at

similar manner with laboratory test conducted by 4mbily and $andhi "%&&:(. The test model use

:+


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steel mould and cylindrical tube glue with geogrid encasing the tube are place inside it. Stone

material is pour inside it and being compacted for a diameter of +& mm and B+ mm with its

height is twice of its diameter. The test model is place at the triaial apparatus and result from the

triaial test are collected and analysed by -345#S. The graph for both laboratory eperiment

and -345#S are plot together and compared with each other. 9igure %.)B shows the result of

triaial test conducted by Malarvihi and #lamparuthi "%&&6(. The dotted line is the result from

-345#S analysis while the straight line is the result for laboratory eperiment.

0i*ure 2.36 Tria


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"%&&6( and 4mbily and $andhi "%&&:( had being succeed in proving the accuracy and reliability

of the software itself. Ta!e note that both of them use finite element program called -345#S

which we can conclude that -345#S software are most reliable software for simulation of the

soil interaction with stone column. That is why for this research paper we used -345#S mainly

for assessment of our research without the need of doing actual eperiment as the -345#S itself

can simulate the eperiment very well and accurate.

2.3 Ot/er re#earc/ ;/ic/ u#ed P(A>IS a# t/eir main #o"t;are.

Many researches had used -345#S to verify their result. Some research even use

-345#S mainly without doing and actual eperiment as it cut the cost needed for an eperiment

and save time as -345#S can give result within a minute and even within seconds.


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the bulging of column, stress distribution at the stone column and soil, settlement of the soil, and

the stability of the reinforced soil wall. 4ll the parameters are evaluating using -345#S.

Cortlever and $utter "%&&%( recently were doing a research which use -345#S software

to verified the design calculation which use ritish standard as their code of design. 9rom the

research it is found that accurate determination of tensile strength can be obtain through

numerical approach due to consideration of -345#S to ta!e the effect of boundary condition into

account. abu and Singh "%&&'( used -345#S %d version to simulate the nail structure in the

soil and evaluate its behaviour and performance. 9igure %.)6 shows the finite element model for

the nail structure.

0i*ure 2.3: 0inite element model o" nail #tructure 7abu and Sin*/4 2558.

2.% -a& o" Re#earc/

Table 2.15$ap of research.

o


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* Malarvihi and

#lamparuthi

To evaluate

mechanism of

encased stone column

%&*& 3oad is applied at both soil and

encased stone column.

Malarvihi and #lamparuthi only

applied load at column area.

% lloue and

ouassida

To predict the

settlement by a group

of stone column

%&&' This research studies only on

single encased stone column but

lloue and ouassida studies

about group of stone column.

) Malarvihi and

#lamparuthi

4nalysis of

encapsulated stone

column using

numerically analysis.

%&&6 3oad is applied at both soil and


Malarvihi and #lamparuthi only

applied load at column area.

: 4minaton Marto

et al.

To analyse the

performance of

reinforced stone

column using finite

element method.

%&*) 4minaton Marto et al. only

focused on bearing capacity of

the encased stone column. This

research widen the studies about

encased stone column by

studying impact of settlement

with time, ecess pore pressure

with time, and effective stress

with time.

+ 3ee et al. 9ield 3oad Tests of

ncased Stone

Columns in Soft

$round

%&&6 3ee et al. only s tudy on load

settlement behaviour and lateral

displacement of the encased

stone column. This study covers

:'


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lot more such as ecess pore

pressure, effective stress, and

hoop force.

? Kataf and

abipour

perimental

investigation on

bearing capacity of

geosynthetic

encapsulated stone

columns

%&*) Kataf and abipour only study

on bearing capacity of the

encased stone column. This

study covers lot more such as

ecess pore pressure, effective

stress, hoop force, lateral

displacement.

B 1hairul 4syraf

in

1hairuddin

To analyse various

modulus value of

geotetile encasing the

stone column by using

-lais.

%&*)

2.' T/eoretical 7ac@*round

Table 2.11Theoretical bac!ground

o TheoryDConcept KypothesisDquation referenc

es

* The modulus value of geotetile

will affect the hoop force acting at

the geotetile.

The higher the modulus values of

geotetile, the more increase the

hoop force.

7

% Settlement of soil effect by the

stress distribution of soil.

The higher the stress absorb by the

soil, the settlement occurred at the 7

+&


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soil increased.

) Settlement is effected by time. Settlement increased rapidly and

then decrease gradually as time

passed.

7

: ffective stress is affected by

period of time.

ffective stress will increase as

time passed but the increment will

be more linear at latter stage.

+ cess pore pressure is affected by

time.

cess pore pressure will increase

rapidly during plastic stage and will

gradually decrease at consolidation

stage until it reaches the value near

ero.

CHAPTER 3

ETHODO(O-B

3.1 Introduction

Methodology is among the most important step in the research. Commonly many new

researchers don=t give attention to the detail of methodology. #mproper planning of method for a

research always leads the research to disrupted end. 4s many greatest people in the world always

quote Ebetter planning for failure than failure to planning. -lanning is essential as it can prevent

time wasting as every step of research are well prepared and not decide spontaneous, can reduce

cost of research as it remove unnecessary step and simplify method of research, obstacles can be

+*


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detect early and pre7 elimination step to counter it can be plan early through proper planning and

act.

The common step of research always starts from literature review. 3iterature review is

part of research step where all the information gathered, past research from many authors,

/ournals, articles, are collected, analye and summarie into a form of literature and every

contribution of the research are cited with the name of the author. et method is always

sub/ective and not fied as it depends on the type of research, suitability and time constraint.

Sometimes it can be a survey, laboratory eperiment, software analysis or all of it, usually

depends on the result we want to obtain. #n this research paper the method use after literature

review is software analysis only. 4fter gathering all information and data for literature review,

software analysis is carried out to process the whole data and produce the result which is needed

to produce outcome for this research paper.

The ob/ective of this research can be achieved through literature review and software

analysis using -345#S. Software analysis is done by using geotechnical based software which

used finite element as their cored calculation that is -345#S. -345#S can produce all essential

data needed to etract the outcome of the research and ma!e conclusion based on the outcome.

IS

-345#S is a finite element based program which is used by many geotechnical engineering

department to analye and simulate many soil based problem. Unli!e many software, -345#S

does not confine itself to evaluation of soil, but also /ump itself to simulate and analye nail

+%


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structure, tunnel, reinforced wall installed at soil, etc. -345#S is a common choice due to its

simplicity and user7friendly feature. ew user can learned to used it within a day and aGeven

after an hour=s playing through the software feature. -345#S provide many features which is

useful and essential for many applications. 9igure ).* shows feature contain in -345#S. #t can

be seen that some of the features -345#S provide is line drawing tools, plate tools, hinge and

rotation tool, geogrid, anchor, tunnel, standard fiities, many types of load for eample point

load and distributed load, drain, well, material set tool, mesh generation tool, initial condition

tool, and many more. More than ten tools are provided which are more than enough to simulate

many geotechnical engineering based problem encountered.

0i*ure 3.1 Set o" tool# &ro!ide in P(A>IS.

9or this research, -345#S %d version 6.% will be used as main software for analysis of stone

column encased with stone column with various value of modulus of geotetile. -345#S comes

with many version as it is !ept updated every year with every latest version comes with new

features and less bug. The latest version of -345#S is come with )d features which give etra

dimension and advantages compare to older %d version of it. ut although the )d version of

-345#S provides many set of tools, it also is a disadvantage to it as many features means that it

will li!ely to be more comple for first time user and not very user friendly compared to %d

version. -345#S version %d interface is shown as in 9igure ).%.

+)


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0i*ure 3.2 P(A>IS 2d inter"ace.

There is a big difference of interface between those versions of -345#S. See that -345#S %d

version 6.% are more simpler and clear and clean interface compared to the -345#S )d version

which the model needs to be built in )d and consume lots of time with many additional step. 9or

this research -345#S version %d is suitable as stone column interaction with the soil can be

simulating very well by this version of -345#S. -345#S %d also provide geogrid tools which is

essential for this research as stone column which need to by analyed are encased by the geogrid

encasement, so geogrid tools can simulate the geotetile very well and various modulus for the

geotetile can be set and change many times.

+:


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3.2 0lo; C/art o" et/odolo*$

9low charts of this research are shown in 9igure ).) which demonstrates the methodology of this

research which is the guideline for every step ta!en in this research.

++

#roblem Statement

$iterature %eview

To determine effective

vertical stress and settlement

of composite encased stone

column with various modulus

of geotetile.

To simulate the interaction

between encased stone

column and soil layer by

using -345#S finite element

software pac!age.

To produce graph based on soil

and stone column data such as

settlement versus time, cess

pore pressure versus time,

effective stress versus time, and

stress versus settlement.

-lais input


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0i*ure 3.3 0lo; c/art o" met/odolo*$.

3.3 P(A>IS INPUT

#nitial step needed for input using -345#S to set up the parameters need to simulate the stone

column, geotetile casing, and soil layer. ut first we needed to set up the model in *+7triangular

node element and the model is set up to aisymmetry model and gives the name of the pro/ect.

The process of this setting is shown in 9igure ).: below.

+?

-lais calculation

-lais ouput

-lais curve

-lais analysis

Conclusion


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0i*ure 3.% Setu& &roce## o" &roect in P(A>IS.

4fter everything is set, the net process is to draw the layout of the model. The model is draw by

half of its diameter and horiontal length as it is an aisymmetry model not a plain strain model.

The model properties are set based on these parameters@

Model properties@

*.diameter column @ &.&*& m

%.diameter model @ &.*+ m).Column and Soft Soil material

:.Use rigid plate on top of the model and cover the whole model.

The process of drawing the layout for the stone column and soil are shown in 9igure ).+ by using

geometry line tools in -345#S.

+B


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0i*ure 3.' Dra;in* &roce## u#in* *eometr$ line tool#.

4fter finished drawing the shape of stone column and the soil based on its diameter, length and

height set on the model properties, the net step is to apply plate at from the top corner of the

stone column across the soil until it reach the top corner of the soil. The plate is draw by using

plate tool. 9rom 9igure ).? we can see the process of drawing plate across the model and ta!e

note that the plate line is the line with blue color. The plate then is set based on parameter

mention before.

+6


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0i*ure 3.) Proce## o" a&&l$in* &late at to& o" model.

4fter drawing the top plate line, the geotetile is applied at the right side of stone column from

top to bottom of stone column. The geotetile are draw by using geotetile tools provide in

-345#S. The geotetile line is in yellow color and can be seen in 9igure ).B. The geotetile

properties such as its stiffness value will be set up later.

+'


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0i*ure 3.6 Dra;in* &roce## o" *eote


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0i*ure 3.: Standard "i


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0i*ure 3.8 A&&l$ &roce## o" material.

4fter process of applying material are done and both the plate material and geotetile material

are set, distributed load are applied on the top of the plate across the length of the model li!e at

9igure ).*&. 4fter that the mesh are produced by applying the generate mesh button on -345#S.

The generated mesh can be seen at 9igure ).**. The net process is setting up initial condition

for the model. The closed flow boundaries are applied at all side surfaces ecept at the top

surface of the column to allow movement of water up to the stone column. $round water table

are set at the top of the soil. 9igure ).*% shows the detail figure of initial condition setting. 4fter

setting up initial condition, we set up the setting for calculation process which is the last step for

input process. The set up of calculation are shown in 9igure ).*). oted that plate and geogrid

both need to be activated by define button in the parameter section. The geotetile materials are

set its stiffness values at the lowest test value for the first calculation and increase its value for

the net and net calculation. The stiffness value is varied to achieve the ob/ective of this

research which is to assess the impact of various modulus of geotetile to the parameters of the

soil.

?%


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0i*ure 3.15 Di#tribute load a&&lied at to& o" model.

0i*ure 3.11 -enerated me#/ model.

?)


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0i*ure 3.12 Initial condition "or t/e model.

0i*ure 3.13 Calculation &roce## o" P(A>IS.

?:


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3.% P(A>IS OUTPUT

The net process after calculation is the output process. 2utput process produced the deformed

mesh due to stress and applied load. The magnitude of deformation or settlement is based on the

various parameters such as value of distributed load, parameters of soil, stone column and

stiffness value of geotetile. 9igure ).*: below show the deformed mesh of the whole model.

The total displacement of the soil is stated at the output. 9rom the 9igure ).*: it can be clearly

seen that the node element of the model are move from their original place due to deformation of

the model. The output also can show many types of figure such as ecess pore pressure behavior

of the soil shown at 9igure ).*+.

0i*ure 3.1% De"ormed me#/ o" "inite element model.

?+


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0i*ure 3.1' E


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0i*ure 3.1) P(A>IS Cur!e in&ut inter"ace.

4fter input the parameter for the graph, -345#S will produce the graph based on data obtain

through the initial process of input, calculation and output. The whole process is repeated starting

bac! from the calculation part where the stiffness values of geotetile are increased and new

graph will be produced. The new graph will be different from the old graph in term of graph

gradient as result for both are difference due to both having different stiffness value of geotetile

layer. The process is repeated for about + times and each time the process is repeated, the value

of geotetile will be increase so that from the result we can assess the impact of various modulus

of geotetile encasing the stone column to improving the condition of the soil.

?B


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3.) CONC(USION

4fter the graph had being plot by -345#S software curve program, the conclusion could be

produce whether the ob/ective of this research would be achieved or not. 4t this part, the

conclusion for evaluation of stone column with various modulus of geotetile encasing the stone

column could be determine. 9rom the conclusion, the recommendation can be made as whether

to give encouragement for engineers to used higher stiffness value of encased stone column

compared to the lower stiffness one or discourage them if the result stated that increase in

stiffness give adverse impact to performance of stone column.

CHAPTER %

?6


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RESU(T AND ANA(BSIS

%.1 Introduction

4nalysis of various modulus of geotetile is performing in this chapter.


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improve the soil greatly in term of settlement. #ncreasing the stiffness value of geotetile to ?&&,

6&& and *&&& will still improve the soil settlement behavior but the increment is not significant

between those stiffness values in term of improving the soil settlement. y increasing stiffness

value from %&& to :&& the increment is 6), from :&& to ?&& the increment is much lower that is

+.?, from ?&& to 6&& is ).% and from 6&& to *&&& is B.). y loo!ing at the percentage,

increasing the geotetile stiffness value by larger margin for eample from 6&& to *?&& will be

more beneficial in term of performance wise and financial wise. The trend of this graph also had

similar trend with settlement time graph by Castro et al. "%&*)( at 9igure :.%.

0i*ure %.2 Settlement time *ra&/ b$ Ca#tro et al. 2513.

%.3 E


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9igure :.) show the ecess pore pressure versus time graph. 9rom the graph, we can see that

ecess pore pressure build up at the soil decreasing as the stiffness of the geotetile encasement

of the stone column increase. This is due to ability of stone column to absorb the applied stress

which the rate of absorption is greatly improve when encased by higher stiffness value of

geotetile. The ecess pore pressure build up at the soil increase during the plastic stage which

the ecess pore pressure built up is directly effect by the intensity of applied load. 8uring

consolidation stage the ecess pore pressure then showing gradual decreasing until ecess pore

pressure achieve a value near to ero which shown that the soil had achieved a completed

consolidation.

0i*ure %.3 E


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9igure :.: show the effective stress versus time graph at the soil. 9rom the graph, we can see that

increasing the stiffness of geotetile encasing the stone column reduce the effective stress on the

soil. y increasing stiffness value from %&& to :&& the increment in reduction of effective stress

at the soil is )6.B, from :&& to ?&& the increment is %+.6, from ?&& to 6&& is *'.)+ and

from 6&& to *&&& is *?. #ncreasing the stiffness from %&& to :&& can cause great reduction of

effective stress on the soil but increasing the stiffness from :&& to ?&& does not give significant

change of effective stress on the soil. This shows that using higher increment for eample

increasing the geotetile stiffness from :&& to %&&& will give more significant improvement.

9igure :.+ show the effective stress acting on the column, as the effective stress increase the

stiffness of geotetile increase. This shown that increase in stiffness of geotetile can improve

the ability of the stone column to absorb the load applies at nearby soil thus reducing the

settlement of the soil.

B%


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0i*ure %.% E""ecti!e #tre##?time *ra&/ at t/e #oil.

0i*ure %.' E""ecti!e #tre##?time *ra&/ at t/e enca#ed #tone column.

%.' E""ecti!e #tre## di#&lacement relation#/i&

ffective Stress7displacement graph for the encased stone column is shown at figure :.?. This

graph illustrates the performance of the reinforced stone column in term of load carrying

capacity. #ncreasing the stiffness of geotetile improve the load carrying capacity of the stone

column. This is due to ability of higher stiffness of geotetile to provide better confinement

pressure and thus reduce the tendency of the stone column to bulge which can improve the

ability of the stone column to transfer vertical stress to the lower part of the soil. #ncreasing the

stiffness of geotetile to from %&& to :&& improve the load carrying capacity greatly compare to

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:&& to ?&&, ?&& to 6&& and 6&& to *&&&. The trend of the graph also confirmed by 4minaton et

al. "%&*)( at 9igure :.B.

0i*ure %.) E""ecti!e #tre##?di#&lacement *ra&/ at t/e enca#ed #tone column.

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0i*ure %.6 Stre##?di#&lacement *ra&/ at t/e enca#ed #tone column

Aminaton et al.4 2513.

%.) Hoo& "orce anal$#i#

Koop force for various stiffness of geotetile also being analyed in this research. The hoop

forces for all geotetile with different stiffness are tabulated in Table :.* below. 4s we can see

from the table that hoop force acting on geotetile increase as the geotetile stiffness increase.

This had also being confirmed by Malarvihi and #lamparuthi "%&*&( through his founding at

9igure :.6.

0i*ure %.: Hoo& "orce "or di""erent #ti""ne## *eote


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lateral confinement to prevent the stone column to bulge. Koop force produced on the geotetile

layer when stone column deform in horiontal direction which produced horiontal strain. Table

:.% below show that increase the stiffness of geotetile encasing the stone column reduces the

lateral deformation of the encased stone column. This prove that increasing stiffness of geotetile

can reduce the tendency of the encased stone column from bulging, which result from increasing

hoop force induced by the geoteile.

Table %.1Koop force for geotetile with different modulus.

$eotetile Stiffness

"!Dm%(

Koop 9orce

"!Dm(

%&& %.&6

:&& %.:%

?&& %.'6

6&& ).:&

*&&& ).?6

Table %.23ateral deformation for encased stone column.

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$eotetile Stiffness

"!Dm%(

8eformation"U(

"mm(

%&& &.&:*%

:&& &.&*:%

?&& &.&*%B

6&& &.&**%

*&&& &.&*&&

CHAPTER '

CONC(USION AND RECOENDATION

'.1 Conclu#ion

This research aim is to analye the relationship between displacement and time, ecess pore

pressure versus time, effective stress versus time, and effective stress versus displacement. Koop

force and lateral displacement also had being analyed in this research. The following conclusion

are made based on the result obtained.

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*. Stiffness of stone column geogrid encasement effect the displacement of the soil. #ncrease the

stiffness of geotetile encasing the stone column will decrease the settlement of soil around

the stone column.

%. cess pore pressure for soil around the encased stone column will increase rapidly during

the plastic stage and will start to decrease gradually during the consolidation stage until it

achieve value near to ero which means that the soil had achieved complete consolidation

and all water had being squeeed out from the soil.

). ffective stress at the soil around the encased stone column will decrease if the stiffness of

the geotetile encasing the stone column increased. This is due to large proportion of load

carried by the encased stone column. 9or effective stress at the encased stone column,

increase in stiffness of the geotetile encasing the stone column will increase the effective

stress at the stone column.

:. #ncrease in stiffness of geotetile encasing the stone column will improve the bearing

capacity of the soil. ffective stress versus displacement graph showing the sign of

improvement as the geotetile of the stone column encasement increase. This means that the

encased stone column can carried higher load without failing or bulging when it=s bearing

capacity increase.

+. Koop force induces by geotetile increase as the stiffness of geotetile increase. This in turn

provide more confinement pressure to the stone column resulting the stone column to

increase in bearing capacity and reduce the susceptibility of the stone column to bulge.

?. Koriontal displacement of the soil decrease as stiffness of geotetile increase. #ncrease in

stiffness of geotetile encasement will increase the hoop force produce by the geotetile

which provide more confinement pressure and thus reduce the lateral displacement occurred

at the encased stone column. 8ecrease in lateral displacement of the encased stone column

reduces the load transfer from the stone column to the soil which results in settlement

reduction of the soil.

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B. #mprovement of stiffness encasement for the eisting encasement of stone column should be

in increment more than *&&& to give more significant improvement than the eisting

encasement. #ncrement below than *&&& will give little impact to the improvement of soil.

'.2 Recommendation

9or future study on various modulus of geotetile encasing stone column, it is recommended to

do the following things order to etent the scope of this study@

*. Use different type of stone material for the encased stone column to see the interaction

between stone column material geotetile reinforcement.

%. Studies on impact of encased stone column in improving double layer or triple layer of

soil. ach layer consists of different type of soil.

). -roduce stress versus strain graph and do analysis based on the graph obtained and

compared the result with other or similar research.

:. #nstead of focusing on interaction of single encased stone column, future studies can

eplore the interaction of encased stone column in a group which consists of % or more


+. 4pplied different type of loads at the model. 9or eample applying point load at different

point of the soil.

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effect of different modulus elasticity of geotextile encasing the stone column to the strength of...

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