Evaluation of Stone Columns versus Liquefaction Phenomenon

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Evaluation of Stone Columns versus

Liquefaction Phenomenon

Arsalan Salahi1, Hamed Niroumand2, Khairul Anuar Kassim3

1 Master student, Department of civil Engineering, Faculty of Engineering,

Islamic A. University, Central Tehran Branch, Tehran, Iran2Post-Doctorate, Department of geotechnical engineering, Faculty of civil

engineering, Buein Zahra Technical University, Iran3 PhD, Department of geotechnical engineering, Faculty of civil engineering,

Universiti Teknologi Malaysia

ABSTRACTLiquefaction is a phenomenon which has caused various inherent defects in buildings and

structures in recent years. It is therefore imperative to become familiar with this important

phenomenon in all aspects of Civil Engineering practice and technology. Liquefaction occurs in

cohesion less soil. Liquefaction is more pronounced during earthquake in which excess pore pressure water increases considerably during cyclic loading. In other words, if effective stress

becomes nil during such increase, then Liquefaction is the outcome and in fact, liquefaction occursas sand boil, losing its load bearing capacity. There are many techniques currently available that

could prevent liquefaction. One such technique is to use stone columns which are the subject of

this article.

KEYWORDS: Liquefaction, earthquake, soil improvement and stone column

INTRODUCTION

One of the many destructive events that occur during an earthquake is liquefaction which in

recent years has resulted in enormous amount of damage to the buildings and structures.

Understanding the behavior of liquefaction and the parameters that contribute to its behavior is very

necessary in today’s engineering field. In the past three decades considerable research on this have

taken place results of which could give an insight into this important phenomenon, however there are

still some perceived gaps that need further research and studies. Stone columns are known as rammed

aggregate piers, Geo piers or granular columns which are useful technics in reducing liquefaction.

Stone columns ware first used in France in 1830 as soil reinforcement, but it was not until 1950s

when stone columns were widely used in Europe for soil strengthening as well as being utilized onseveral project is the US in 1970’s. The background use of stone columns is the use of material with

high shear strength that in turn produces lateral resistance in the soil. Stone column is a soil

improvement method that will reduce the settlement in foundations and increase load bearing capacity

of the soil. This involves replacement of 15-35% by volume the unsuitable soil by excavating some

wells with certain diameter, depth and spacing relative to each other and filling them with sand,

gravel or aggregate layers followed by compaction of each layer with vibrating equipment to form

vertical columns. In this paper all of the results gathered have been analyzed through a

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Vol. 20 [2015], Bund. 2 740

comprehensive literature review which has been presented. Where a perceived gap is identified this

has also been recommended for future research.

Kumar [1] has presented a way of liquefaction mitigation for a site placed in a floodplain area of

America which is prone of seismic and liquefaction hazards. Deep dynamic compaction has been

used to improve the mentioned site, but because of not being suitable for over than 6 to 9 meters, thesoil improvement has been achieved by installing stone columns. This new method of soil

remediation has impressively changed the soil properties. Some of the advantages of using stone

columns, especially in liquefiable saturated loose sands and sandy soils containing fine grains, can be

summarized as: 1. Soil compaction in lower depths and reducing liquefaction potential. 2. Improving

load bearing capacity of foundations. 3. Economic benefits of stone columns in comparison with

piles. 4. Ease of implementation causing time consuming benefits. 5. The complete consistency of

SPT value with the recommended values for compaction

In the following, there is shown the way of DDC implementation.

Figure 1: Deep Dynamic Compaction [1]

Tsukamoto et al. [2] conducted multiple series of experimental large-scale hollow cylindrical

torsional shear tests on clean fine sand, to study the degree of soil densification properties caused by

static sand pile driving installation which is achieved by simulating stress changes of a soil element in

the neighborhood of pile penetration. On this basis, they provided a diagram to help evaluating the

degree of soil densification effects, so that the SPT N1 value was achieved. They also took

advantages of some case studies which have recently been done at three sites in Japan. To cover the

whole of soil improvement area for an in-situ investigation, they installed several sand compaction

piles with an equal spacing. They also analyzed the stress changes in the field during the pile

penetration based on the classical elasticity theory. They applied sequential stress changes to

saturated spciments which have been prepared in a torsional hollow cylindrical shear test apparatus.

They found that a sufficiently great volume change will occur in the specimens, which can bring

about substantial densification in the sand. They reported that densification under drained conditions

was not great enough to cause volume decreases corresponding to that likely to occur in the field. In

the following picture the installation of sand compaction piles has been shown.

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Vol. 20 [2015], Bund. 2 741

Figure 2: Sand pile installation steps

Rudolph et al. [3] has presented a case study of using impact rammed aggregate piers (RAPs) for

a site in the vicinity of Colma Gulf by the aim of reducing its liquefaction potential. The project is

within a mixed residential, commercial, and light industrial area of California. The site contains

liquefiable sandy clay soil with a low plasticity index and mean compression. Their study includes the

results of a pre and post-ground improvement Cone Penetration Test (CPT) program that has been

implemented to evaluate the post-ground improvement liquefaction and seismic settlement potential.

In their investigation, they have only focused on the soil compression near the RAP without paying

attention to reducing pore water pressure built up or improving site stiffness that can be studied later.

The engineering result of this investigation is that using RAP will reduce the liquifaction potential of

seismic areas. One other engineering advantage of it, is time-dependent liquifaction reduction that is

deduced from it’s CPT penetration resistance. The following picture is related to RAPs configuration

in site.

Figure 3: Rammed Aggregate Piers improvement plan [3]




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Okamura et al. [4] described the results of in-situ tests, conducted at three sites where foundation

soil were improved by vibratory or non-vibratory sand compaction pile techniques. They also

obtained high quality undisturbed samples at each site by the in-situ freezing method and carried out

cyclic triaxial and shear tests on them.These triaxial specimens obtained from frozen samples, were

fully saturated in the triaxial cell. They also discussed about spatial distributions on SPT N-value and Nd -value which were obtained by rotary ram sounding. Besides, they compared the relationship

between liquefaction and N-value of natural soil deposits during an earthquake, which was achieved

by field evidences of earthquake. They used the test results, to verify the applicability of conventional

method in assessing liquefaction resistance of soils improved by sand compaction piles. By the

results, they concluded that penetration resistance is highly heterogeneous and randomly distributed

in a horizontal plane at any depth. Another engineering result of their study is that neither vibratory

compaction piles nor non-vibratory sand compaction pile cannot increase significantly the

liquefaction resistance of soils near the ground surface. Another conclusion of this study is that there

is good correlation between the liquefaction resistance and mean value of Nd , which have been

obtained from several locations. The results show that the liquefaction resistance of the improved

sand is considerably higher than those obtained from N-value based conventional method which is

only available for fully saturated soils.Adalier et al. [5] has prepared the results of dynamic centrifuge tests conducted by the aim of

assessing stone column performance against liquefaction phenomena in non-plastic silty soils.

The effect of stone column on stiffness improvement of considered site has been evaluated.

The tests have been conducted on four different conditions of silty specimens:

- With or without stone column

- With or without surcharge

All analyses have been done based on dynamic excitation conditions and recorded dynamic

responses. Some of the important conclusions of these experimental studies are:

- Using stone column is an effective technique to mitigate the liquefaction potential of

cohesionless silty sands.

- Stone column can partly rebate the excess pore water pressure build-up

- Stone column is an effective method in increasing the stiffness of foundation soil

- The mentioned method can significantly reduce the foundation settlement caused by effective

surcharge (up to 50%).

In the following, it has been shown the stone column configuration in the models.




Vol. 20 [2015], Bund. 2 743

Figure 4: Cross-sectional and plan view of stone colmns in /model 2 [5]

Adalier and Elgamal [6] have investigated the current state of stone column technologies as an

effective method in mitigating liquefaction phenomena. In this paper, it has been conducted a review

by four important purposes: (a) Defining key considerations for using stone columns as a liquefaction

countermeasure, (b) Providing insights for designing and construction of stone columns, (c) Preparing

the latest advancements in researches and (d) Presenting the useful information resources. They

gathered a comprehensive list of significant publications that discuss stone columns as a seismic

liquefaction countermeasure in North America, Europe, and Japan. Also different applications of

stone columns have been mentioned here. At last, it must be mentioned that the installation method of

stone columns has a direct effect on reducing liquefaction potential, also stone column should be

designed to reduce clogging and loss of drainage effectiveness. The following picture shows the wayof modelling stone column by shaking table.




Vol. 20 [2015], Bund. 2 744

Figure 5: Cross sectional view of model used in shaking table tests [6]

Shenthan et al. [7] developed an analytical methodology to evaluate the effectiveness of vibro

stone columns and dynamic compaction techniques together with pre-fabricated vertical drains by the

aim of increasing compression and mitigating liquefaction in saturated sands and cohessionless silty

soils. The improvement of designing guidelines to compact silty soil with the use of stone column and

dynamic compaction together with key parameters of soil reinforcement have been discussed in this

paper. In order to analyzing the soil compression by the use of stone column and dynamiccompaction, some numerical methods have been developed. In this study, the main soil properties and

stone column designing parameters for sands and saturated cohessionless silty soil have been

introduced. One of the important engineering advantages of this study, is preparing the design chart of

stone column and dynamic compaction in order to liquefaction potential mitigation. This method will

also reduce the consolidation time and improves the drainage rate. The computer modelling presented

here, is a proper method in analyzing stone column and dynamic compaction of different soils. In the

following, it has been shown a stone column together with wick drain.




Vol. 20 [2015], Bund. 2 745

Figure 6: Vibro stone columns and composite vibro stone columns [7]

Sadrekarimi and Ghalandarzadeh [8] discussed two famous improvement methods of mitigating

liquefaction consisting gravel drains and compacted sand piles, which also have been compared at the

end. They conducted some precisely prepared 1g vibrating table tests by considering these methods.

These tests have been done in two cases of containing improvement method and without it, in which

the accelerations, pore water pressures and settlements are evaluated during the tests. They compared

the results to each other which drives this conclusion that compacted sand piles are more efficient

than gravel drains in case of liquefaction resistance and settlement of the subsoil during the shaking

period. Nevertheless, after shaking, the efficiency of the gravel drains is getting better by the means

of dissipating excess pore water pressure. They reported that the resistance to liquefaction could be

improved considerably by compaction, compared with the use of gravel drains. They concluded that

both gravel drains and compacted sand piles can retard excess pore water pressure build-up. The

engineering benefit of their comparative study is that the compaction method can better reduce the

settlement than gravel drains.

Homoud and Degen [9] have discussed about designing stone columns in seismic areas andguidelines for Marine Stone Columns designing against liquefaction. They described the new

patented Marine Double-Lock Gravel Pump, which is an innovation in marine stone columns

technology. Some of the main engineering benefits of this technique are: high speed implementation,

cost-effective construction and liquefaction mitigation in seismic areas. By the use of guidelines

presented in the paper, the engineers are capable of deducing suitable quality indexes for stone

column designs. In the following, there is shown a schematic view of implementing marine stone

columns.




Vol. 20 [2015], Bund. 2 746

Figure 7: Marine Gravel Pump unit [9]

Rollins et al. [10] presented a case history in which pre-fabricated vertical drains were used in

connection with stone column treatment for a 4 meters thick layer of liquefiable silty and sandy silt. It

can be deduced from this study that the mentioned method can only be suitable for the soils with fines

percentage lower than 20%, otherwise the least effectiveness of this method will be achieved. Some

of the main engineering benefits concluded from this investigation are:

1- Using stone column together with wick drain will significantly improve the NSPT value.

2- If the stone columns spacing has decreased from 2m to 1.8m, the effectiveness will increase

up to 60%.

In the following, a view of stone column plan containing wick drains is shown.

Figure 8: Schematic view of stone columns and wick drains [10]

Krishna et al. [11] evaluated the liquefaction mitigation of the ground reinforced by granular piles

by considering the pore pressure build-up and dissipation accounting for both the densification and

drainage effects of granular piles. In this study, the modified Seed and Booker’s model (1977) for

computing the densification effect of granular piles and excess pore water pressure has been applied.

By the use of this new modified model, the effect of Rammed aggregate pier densification can also be

considered. Some of the engineering considerations of this investigation are listed below:




Vol. 20 [2015], Bund. 2 747

- If the vertical drainages spaces are increased, the pore pressure rate will decrease and

increases with cyclic ratio increase.

- The effect of densification by regarding the coefficients of volume change and permeability,

can be positive or negative proportion to relative compaction degree.

Madhav and Krishna [12] have evaluated different mechanisms that are effective in the operationof granular piles as a ground improvement method for liquefaction mitigation. The different effective

mechanism is Drainage, Reinforcement, Storage, Dilation and Densification which have been studied

in details. At last, it has been proved that granular pile is a very effective technique in reducing

liquefaction potential of seismic areas. In this paper, generation and dissipation of excess pore water

pressure have also been investigated. Some of the engineering applications of granular piles comprise

its effectiveness in drainage, soil compression in the neighborhood of piles and soil reinforcement.

The most important mechanism of granular pile is dissipating excess pore water pressure as fast as

generating it.

Ranjbar Malidare and Janalizadeh Choobbasti [13] have studied the areas along the Caspian Sea

which contain saturated sandy soil together with high groundwater level that led to liquefaction

potential.They revealed the high efficiency of this technique for decreasing the risk of liquefaction, byusing numerical analysis software (FLAC), field explorations and laboratory tests. One of the most

important engineering benefits of installing stone column is the reduction of excess pore water pressure. In the following table, some of the most important results of this study have been presented.

Table 1: A summary of the results of analysis [13]

Krishna and Madhav [14] evaluated the densification of reinforced soil caused by dilation as an

effect of RAP reinforcement method, and also the pore water pressure generation and dissipation of

the reinforced ground under earthquake conditions have been explored. They applied the modified

theory of pore water pressure generation and dissipation developed by Seed and Booker(1977), for

evaluating the densification and dilation effects of Rammed Aggregate Piers together, under

earthquake conditions. In this study, by considering the effects of installation and dilation of gravel

column, the liquefaction phenomenon has been analyzed. They concluded that both coefficients of

volume change and permeability, can have positive or negative effect due to compression degree.Another result is that on the basis of different studies, dilation has positive effect on liquefaction, so

we can conclude that both factors comprising densification and dilation, should be considered in

designing stone columns.

Rollins et al. [15] investigated the pre-fabricated vertical drains in conjunction with stone

columns to reinforce sandy soils containing high fines content. No comparison has been made

between the existences of drains or lack of them in their study, but generally improved performance

of stone columns with drains may be achieved. Using pre-fabricated vertical drains in conjunction




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with stone column will significantly increase the NSPT value, however by increasing the fines content,

its effectiveness will decrease, in a way that the layers containing 15% or more clay sized particles,

will have the least effectiveness. Another important result of this investigation is that significant

increases in SPT values with time will be caused in the present of wick drains. The following picture

is a view of stone columns and pre-fabricated vertical drains.

Figure 9: Layout of Stone columns and wick drains [15]

Krishna and Madhav [16] prepared an overview of granular columns toward liquefaction. In this

study, the liquefaction phenomena and its results have been briefly discussed. Also there have been

discussed about some of the different techniques of liquefaction mitigation in seismic areas. The main

approach of this paper toward liquefaction mitigation, is applying granular columns. Different

construction methods of granular columns are discussed. They reported recent developments in the

area of liquefaction by investigating granular conclusions as liquefaction countermeasures, on the

basis of physical, numerical and analytical models. One of the important engineering effects of this

study is that, granular column is a very effective technique in reducing liquefaction potential and

since they also serve as drains, we can use them to dissipate the excess pore water pressure. Different

mechanisms of granular columns such as densification, reinforcement and drainage operation of stonecolumns, can significantly reduce the liquefaction hazards.

Moayedi et al. [17] investigated the behavior of gravel drain piles under intensive earthquake

loading beneath the foundation. To achieve this goal, they selected one of the waste water septic tank

project in north of Persian Gulf in Hormoz Island as a case study to find suitability of gravel drain

pile system to reduce and control excess pore water pressure. Furthermore, they conducted different

tests of soil mechanics to achieve a better understanding of the behaviour of the soil layers during an

earthquake. They also carried out several finite elements modeling and vertical gravel drain analyzes




Vol. 20 [2015], Bund. 2 749

to make such a reduction and/or postponed the time duration of maximum achieved excess pore water

pressure during earthquake loading. They reported that using these drain piles has large effects on the

excess pore water pressure rate and creates a liquefaction zone during an earthquake. Another

engineering benefit of using drain columns beneath the foundation is that, it will reduce the

possibility of liquefaction during an earthquake. Another result is that if the excess pore water pressure rate at the first 10 seconds of earthquake is below 1, liquefaction will never happen. Also

these columns will be effective in increasing load bearing capacity. In the following, a schematic

view of drain piles modelling is shown. In the following picture excess pore pressure water in two

conditions has been shown:

Figure 10: Excess pore pressure in two different items [17]

(a) Without draining system (b) With gravel drain ple system

Singh et al. [18] carried out a number of tests on a small vibration table (shake table) applying

excitations to the ash samples. The purpose of these tests was exploring liquefaction reduction of sand

stone columns with or without fly ash. They also evaluated the excess pore pressure. Another thing to

be studied was the effect of spacing of stone-sand columns on liquefaction resistance of the fly ash.The addition of stone-sand columns increases the liquefaction resistance of the pond ash significantly.

This also decreases the time of generating pore pressure; duration for which maximum pore pressures

stays and total time for dissipation of pore water pressure. As application engineering benefits of this

study, we can say: If column spacing equals to 4d, the liquefaction resistance of pond ash will

increase up to 22%, and for the 3d spacing, the increase will arrive up to 92%. So 3d distance is the

best spacing of columns to reduce liquefaction potential. Easement of implementation, is another

engineering benefit of this method. In the following, there is shown a plan of sandstone columns. In

the following picture schematic view of tests have been shown:




Vol. 20 [2015], Bund. 2 750

Figure 11: Plan of stone columns in shake table in different conditions [18]

Yanmei [19] analyzed the liquefable soil of foundation treated by stone columns, by dynamic

analysis procedure. He also studied on the design parameters of stone column which are effective

against liquefaction. He reported that by increasing the diameter of stone columns, the settlement and

excess pore water pressure decrease, and by increasing the columns spacing, the settlement and

excess pore water will increase too. At the end it must be mentioned that different parameters of stone

columns such as diameter, length, spacing, etc. have important effects on liquefaction. In the

following, a schematic view of stone columns is shown.




Vol. 20 [2015], Bund. 2 751

Figure 12: Schematic view of stone columns [19]

Adalier and Elgamal [20] conducted some dynamic centrifuge tests, to study the liquefaction

remedial effects of stone columns in marine cohessionless silty soils. In their study, they have focused

on the strength benefits, rather than improved drainage and densification caused by columninstallation. The tests have been done in two conditions of exerting surcharge or lack of it, then thetwo conditions have been compared with each other under the same shaking conditions. Based on the

mentioned comparison, they concluded that stone column will partly dissipate the pore water pressure

build-up, increase the stiffness and load bearing capacity of foundation and significantly decrease the

settlement caused by surcharge. They suggested that, the marine stone column method may provide

environmentally friendly and cost effective solution for marine gravity structures on liquefiable soildeposits and can effectively reduce the liquefaction of these soils. The following picture is a plan of

stone columns.




Vol. 20 [2015], Bund. 2 752

Figure 13: Plan and cross-sectional view of stone columns [20]

Shao et al. [21] have studied the effects of stone column and drains in reducing liquefaction

potential of one site in an area of Washington. Also, the designing and construction procedures of

these columns are presented. They determined the soil properties by different tests such as SPT and

CPT. They also analyzed and determined the pore water pressure by using the computer program

FEQDRAIN (Pestana, et al., 1997). This computer program together with post-treatment CPTs, show

liquefaction mitigation as a result of stone column densification and using seismic drains. The

mentioned program will assess the liquefaction potential and lateral spreading. In fact, the analysis

and design of stone column along with seismic drains have been done by FEQDRAIN. The following picture, shows the application of stone column and seismic drain in a site.

Figure 14: Earthquake drain and stone column plan [21]




Vol. 20 [2015], Bund. 2 753

H.P. Singh [22] performed a number of tests on a small Vibration (Shake) Table on the pond ash

samples prepared at relative densities of 20% without and with stone-sand columns at 4d c/c spacing.

For some specimens, the pond ash has been improved by the effect of surcharge loads. He also

evaluated the liquefaction resistance of pond ash, in terms of maximum pore water pressure ratio for

all the tests. He reported that the liquefaction resistance of pond ash increases with the inclusion ofstone-sand columns, and also there is a significant increase in liquefaction resistance of pond ash due

to surcharge loads. He also concluded that by increasing the surcharge loads exerting on the pond ash,

the maximum excess pore water pressure rate will decrease, so the liquefaction potential will be

reduced too. The following picture is a schematic view of stone column.

Figure 15: Location of stone column in shake table tank [22]

Asgari et al. [23] have parametrically investigated the effects of stone columns and pile pinning

on reducing the potential of liquefaction during earthquakes, applying three-dimensional finite

element simulations using OpenSeesPL. At last the two mentioned techniques are being compared to

each other. The main aim of this paper is evaluation of different parameters in reducing liquefaction

potential. They have reported that increasing the structure mass will led to pore water pressure

decrease. Another important conclusion is that the dissipation of pore water pressure in sandy soil is

faster than silts.

Selcuk and Kayabali [24] have developed a finite element computer program which is able to

analyzing the distribution of excess pore water pressure during an earthquake. This computer program

is capable of analyzing the undrained condition before the installation of stone columns as well as thedrained conditions in the existence of stone columns. They applied the modified model of Seed and

Booker (1977). The main aim of this program is determining the appropriate construction of stone

columns in order to reducing the excess pore water pressure in liquefiable soil. The engineering

benefit of this investigation is determining the optimum diameter and spacing of stone columns for

the best protection against soil liquefaction. They reported that by increasing the radial distance

between stone columns, the pore pressure rate increases and reaches its maximum value when the

radial distance equals the radius of influence of the stone columns. Another engineering benefit of

this study, is minimizing the number of stone columns needed per unit area. They also reported that




Vol. 20 [2015], Bund. 2 754

stone columns are utilized not only in preventing the soil liquefaction but also in reducing settlement

and increasing load bearing capacity.

Forcellini and Tarantino [25] presented computational modelling, free field response, and stone

columns remediation assessment. They also conducted a parametric study to assess the effectiveness

of stone column mitigation technique by gradually increasing the extension of remediation, in order toachieve a satisfactory lower level of permanent deformation. Their study is based on the use of a

finite element computational interface that able to analyse the earthquake-induced three-dimensional

pore pressure generation adopting one of the most credited nonlinear theories in order to assess

realistically the displacements connected to lateral spreading. So the aim 2of their analyses was

numerically reproduce Italian Emilia-Romagna Earthquakes (May 2012) allowing several

considerations. They concluded that stone column remediation was so effective in reducing the sand

stratum lateral deformation taking into consideration area replacement ratio ( rr) parameter. They

imparted that mitigation effectiveness and dimensioning design depend on the required performance

to be provided in terms of safety level. As an engineering benefit outcome from this investigation, it

can say that this study can quantify soil performance to liquefaction-induced effects using metrics that

are of immediate use for both pre-earthquake and post-earthquake risk assessment analyses.

Figure 16: Deformed mesh at the end of the motion [25]

Table 2: A comparison between papers conducted on stone columns versus liquefaction

phenomenon in geotechnical engineering.

Authors Year Project goal Application and Methodology

Kumar [1] 2000Liquefaction mitigation in a

floodplain site in seismic area.Use of stone columns and deep dynamic

compaction to reinforce deeper soils.

Tsukamot

et al [2]2000

Study the degree of soil

densification properties caused

by static sand pile driving

installation of stone columns.

Do multiple series of experimental large-

scale hollow cylindrical torsional shear

tests on clean fine sand by simulating stresschanges of a soil element in the

neighborhood of pile penetration.

Rudolph

et al [3]2003

Reducing liquefaction potential

by using impact rammed

Present the results of a pre and post-ground

improvement Cone Penetration Test (CPT)




Vol. 20 [2015], Bund. 2 755

aggregate piers (RAPs) for a site

in the vicinity of Colma Gulf.

program that has been implemented to

evaluate the post-ground improvement

liquefaction and seismic settlement potential.

Okamuraet al [4]

2003

Evaluate foundation soil that

improved by vibratory or non-vibratory sand compaction pile

techniques against liquefaction.

Perform undisturbed samples at each site by the in-situ freezing method and carried

out cyclic triaxial and shear tests on them.

Adalier et al [5] 2003

Evaluate stone column

performance against

liquefaction phenomena in non-

plastic silty soils.

Perform dynamic centrifuge tests on four

different conditions ( with and withoutsurcharge and stone columns).

Korhan and

Elgamaz [6]2004

Mitigating of liquefaction

phenomenon by using stone

column technologies as aneffective method.

Gathering a comprehensive list of

significant publications that discuss stone

columns as a seismic liquefactioncountermeasure in North America.

Shenthan

et al [7]2004

Mitigating liquefaction in

saturated sands and

cohessionless silty soils byusing of vibro stone columns

and dynamic compactiontechniques together with pre-

fabricated vertical drains.

Developing analytical methodology andnumerical methods to evaluate the

effectiveness of vibro stone columns and

dynamic compaction.

Sadrekarimi

andGhalandarzade

h [8]

2005

Discussing two famousimprovement methods of

mitigating liquefaction

consisting gravel drains and

compacted sand piles.

Considering some precisely prepared 1g

vibrating table tests.

Homoud, andDegen [9]

2005

Designing stone columns in

seismic areas and guidelines forMarine Stone Columns

guideline against liquefaction.

Describing the new patented MarineDouble-Lock Gravel Pump.

Rollins

et al [10]2006

Evaluating pre-fabricatedvertical drains in connection

with stone columns for layer of

liquefiable silty and sandy silt.

Evaluating this method in different

conditions which the fine content is

variable.

Krishna

et al [11]2006

Reducing liquefaction

mitigation potential by ground

reinforcing ground by granular

piles.

Considering the pore pressure build-up and

dissipation accounting for both the

densification and drainage effects.

Madhav and

Krishna [12]2008

Considering granular piles as a

ground improvement method forliquefaction mitigation.

Evaluating different mechanisms that are

effective in the operation of granular piles.

Ranjbar

Malidareh andJanalizadeh

Choobbashi

[13]

2008Evaluating the decrease of riskof liquefaction near the Caspain

sea by stone columns.

Using numerical analysis software

(FLAC).

Krishna and

Madhav [14]2008

Evaluating the densification of

reinforced soil caused by

dilation as an effect of RammedAggregate Piers.

Rammed Aggregate Piers reinforcement

method for liquefaction mitigation.

Rollins

et al [15]2009

Reinforcing sandy soils

containing high fines content

Using pre-fabricated vertical drains in

conjunction with stone columns.




Vol. 20 [2015], Bund. 2 756

against liquefaction.

Krishna and

Madhav [16]2009

Presenting an overview of

granular columns toward

liquefaction.

Evaulating different techniques of

liquefaction mitigation in seismic areas and

discussing the results.

Moayedi

et al [17]2010

Evaluating the behavior ofgravel drain piles under

intensive earthquake loading

and also controlling excess porewater pressure.

Using selected one of the waste waterseptic tank project in north of Persian Gulf

to find suitability of gravel drain pile

system.

Singh

et al [18]2010

Exploring liquefaction reduction

of sand stone columns with or

without fly ash.

Performing a number of tests on a small

vibration table (shake table) applying

excitations to the ash samples.

Yanmei [19] 2011

Analyze and evaluate dynamicresponse of liquefy soil under

foundation that reinforced with

stone columns.

Evaluating design parameters of stone

column which are effective against

liquefaction.

Adalier and

Elgamal [20] 2011

Evaluating stone columns as

liquefaction remedial effects inmarine cohessionless silty soils.

Conducting some dynamic centrifuge testsin two conditions of exerting surcharge or

lack of it, then the two conditions have been compared with each other under.

Shao

et al [21]2013

Studying the effects of stone

column and drains in reducing

liquefaction potential.

Designing and construction procedures of

stone columns.

Singh [22] 2013Evaluating the liquefaction

resistance of pond (fly) ash.

Perform tests on small Vibration (Shake)

Table on the pond (fly) ash samples.

Asgari

et al [23]2013

Investigating the effects of stone

columns and pile pinning on

reducing the potential of

liquefaction during earthquakes.

Applying three-dimensional finite elementsimulations using OpenSeesPL.

Selc¸uk and

Kayabali [24]2014

Determining the appropriate

construction of stone columns inorder to reducing the excess

pore water pressure in

liquefiable soil.

Developing a finite element computer program which is able to analyzing the

distribution of excess pore water pressure

during an earthquake.

Forcellini and

Tarantino [25]2014

conducting a parametric study to

assess the effectiveness of stonecolumn mitigation technique

Presenting computational modelling, free

field response, and stone columnsremediation assessment.

CONCLUSIONS

Following a thorough review of the published papers to date on the subject of “stone columns and

liquefaction it can be concluded that stone columns play very important role in soil remediation inareas that are prone to earthquake hence preventing or limiting liquefaction. Stone columns can

dampen liquefaction potential by pseudo drainage effect through granular material, strengthening the

surrounding soil near stone columns and improving the soil foundation under the buildings and

structures.

One of the stone columns tasks in the event of an earthquake is to reduce the liquefaction by

dissipating the pore water pressure build up in the soil as they are occur. Stone columns are very

effective in preventing liquefaction but this would depend on area replacement ratio. Another factor




Vol. 20 [2015], Bund. 2 757

that affects this is extent of surcharge load but this is disputed in the literature review. Diameter of

columns, spacing relative to each other and columns lengths are other contributory factors too.

Negative pore pressure that is created by dilation is also important in liquefaction reduction.

Densification effect near dilation can have a positive role in reducing the liquefaction potential, since

liquefaction resistance can be enhanced by well compacted soil. It should be noted that diversity ofstone columns installations can be an important factor in liquefaction reduction and should be

considered in practice Also pond (fly) ash liquefaction resistance can be inserting by stone sand

columns. To conclude, stone columns are very effective way of reducing the liquefaction potential

and they can be more economical in their construction than other traditional and costly methods.

Based on the existing researches on the stone columns and liquefaction, it is clear that some gaps

are exists that haven’t solved yet now, and should be worked on the future by autures, researchers,

students and related engineers, as these following subjects:

a) Work on stone column behavior and its mechanism during earthquake, especially when

saturated silty and sandy soil exist.

b) For better understanding the behavior of stone columns during an earthquake, whenconstructed in silty deposits, some tests should be done like permeability, diameter or slenderness

effect of columns.

c) There is a wide limitation of stone column case histories and its response during an earthquake,

and also great need for well documented on this subject exists.

d) To delimitate the degree of improvement and the degree of densification or some operational

parameters on degree of improvement that reached by stone columns, no comprehensive analytical

trend exists.

e) Construction of stone columns in marine soils on offshore areas are slow and much expensive.

Solving this problem is necessary for future.

f) When stone columns are constructed in conjunction with wick ( pre fabricated vertical) drains,

no comparisons tests have been done to determine that how much of the improvement is by the stone

column and how much is by wick drain.

g) When stone columns are constructed in silty sand soils with high content of fine particles, its

efficiency remarkably come down. Solving this problem is necessary for the future.

h) Stone columns rigidity in horizontal loads are too small and since its deformation, it causes

large settlement under the structure, so solving this matter is a future need for civil engineering.

i) Silty or clayey soils with low plasticity are vulnerable to liquefaction. Pond(fly) ash reduce this

danger, so some research should be done on this material to reducing the liquefaction hazard.

Guideline

We conclude based on the recent surveys and articles regarding to soil improvement by using

stone column that stone column is known as an effective technique, with other techniques to prevent

Liquefaction phenomenon, to decrease Liquefaction potential in saturated cohesion less soil in areas

prone to having earthquakes. Regarding to last surveys in this case and based on the present articles

following engineering specifications can be known for mentioned technique:

• Densification of surrounding soil of stone column (especially cohesion less soil)

• Dissipation of excess pore pressure water

• Redistribution of earthquake




Vol. 20 [2015], Bund. 2 758

Some of operating & engineering benefits of this technique to decrease soil liquefaction could be

named as an economical technique, high speed in operation and easy to operate.

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Evaluation of Stone Columns versus Liquefaction Phenomenon

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