Evaluation of Stone Columns versus Liquefaction Phenomenon Arsalan Salahi 1 , Hamed Niroumand 2 , Khairul Anuar Kassim 3 1 Master student, Department of civil Engineering, Faculty of Engineering, Islamic A. University, Central Tehran Branch, Tehran, Iran 2 Post-Doctorate, Department of geotechnical engineering, Faculty of civil engineering, Buein Zahra Technical University, Iran 3 PhD, Department of geotechnical engineering, Faculty of civil engineering, Universiti Teknologi Malaysia ABSTRACT Liquefaction 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 occurs as 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 on several 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 - 739 -
Transcript
Evaluation of Stone Columns versus Liquefaction Phenomenon
1 Master student, Department of civil Engineering, Faculty of Engineering, Islamic A. University, Central Tehran Branch, Tehran, Iran
2 Post-Doctorate, Department of geotechnical engineering, Faculty of civil engineering, Buein Zahra Technical University, Iran
3 PhD, Department of geotechnical engineering, Faculty of civil engineering, Universiti Teknologi Malaysia
ABSTRACT Liquefaction 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 occurs as 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 on several 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
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, the soil 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.
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]
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.
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 way of modelling stone column by shaking table.
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 dynamic compaction, 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.
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 and guidelines 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.
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:
- 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 operation of 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, by using 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
Vol. 20 [2015], Bund. 2 748 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 stone columns, 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:
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.
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 column installation. The tests have been done in two conditions of exerting surcharge or lack of it, then the two 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 soil deposits and can effectively reduce the liquefaction of these soils. The following picture is a plan of stone columns.
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]
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 of stone-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 the drained 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 to achieve 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 (𝐴𝐴rr) 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] 2000 Liquefaction 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 stress changes 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)
Evaulating different techniques of liquefaction mitigation in seismic areas and
discussing the results.
Moayedi et al [17] 2010
Evaluating the behavior of gravel drain piles under
intensive earthquake loading and also controlling excess pore
water pressure.
Using selected one of the waste water septic 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 dynamic response 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 in marine cohessionless silty soils.
Conducting some dynamic centrifuge tests in 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] 2013 Evaluating 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 element
simulations using OpenSeesPL.
Selc¸uk and Kayabali [24] 2014
Determining the appropriate construction of stone columns in
order 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 stone
column mitigation technique
Presenting computational modelling, free field response, and stone columns
remediation 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 in areas 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 of stone 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, when constructed 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
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.
REFERENCES [1] Sanjeev Kumar, 2001: ‘Reducing liquefaction potential using dynamic compaction and
construction of stone columns’ Geotechnical and Geological Engineering, 19: 169-182.
[2] Tsukamoto Y., Ishihara K., Yamamoto M., Harada K. and Yabe H. 2000: “Soil Densification due to Static Sand Pile Installation for Liquefaction Remediation”, Soils and Foundations, Vol. 40, No. 2, pp. 9-20.
[3] R.W. Rudolph, B. Serna, and T. Farrell, 2011: ‘Mitigation of Liquefaction Potential Using Rammed Aggregate Piers’ Geo-Frontiers, pp. 557-566.
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