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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 $eneration of ecess water pressure is occurred and is assumed to scatter around the permeable
columns;
7 #ncreased in horiontal stresses, which in result caused the coefficient of earth pressure 1 to
eceed the original rest coefficient, 1o.
7
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2.1.1.1 7earin* Ca&acit$
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
encased stone column.
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.
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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 %
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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.
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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.
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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.
B:
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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
encased stone column.
+. 4pplied different type of loads at the model. 9or eample applying point load at different
point of the soil.
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