Performance Of Stone Columns Research Articles

Liquefaction potential of reinforced soil by stone columns

ABSTRACT Stone column installation is commonly employed to prevent liquefaction. Stone columns mitigate liquefaction by means of mainly three mechanisms which are drainage, stiffening and densification. A factor of safety against liquefaction FS is used to quantify liquefaction potential. The aim of this study was to assess the efficiency of stone columns as a liquefaction remediation based on twenty four case studies. In these cases, SPT and CPT tests were recorded before and after stone columns installation. It was found that the installation of stone columns considerably increased soil density mainly in clean to slightly silty sand. The average rate of increase in the penetration resistance N 1 , 60 , cs and q c 1 Ncs were about 31.13% to 69.29% and 57.10% to 318.28%, respectively. Furthermore, the cyclic shear stress ratio of reinforced soil can be reduced by 13.5% to 77.5% due to the stiffening improvement of stone columns. Densification and stiffening mechanisms have been investigated through several approaches. Their individual and combined effects have been analysed. Comparative results indicate that considering the densification and stiffening effects in liquefaction analyses improved considerably the performance of stone columns.

Model tests on ordinary and geosynthetic encased stone columns with recycled aggregates as filler material

PurposeSincethe availability of natural aggregates is very sparse, recycled industrial and construction waste provides a sustainable alternative to ground improvement using vibro replacement method. Utilizing recycled building waste caters the requirement for its disposal and offers an effective remedy for the scarcity of natural resources. The aim of this study was to give a sustainable alternative for the natural aggregates as the material for stone column.Materials and methodsA good stone column material should be hard, dense, chemically inert and must comply with the size requirement. The utilization of construction debris and spent railway ballast as column material has been the subject of numerous researches. This work focuses on finding the suitability of railway ballast and concrete debris as alternatives for stone column material. A detailed laboratory testing of these materials has been carried to judge their strength requirements as the material for both Ordinary Stone Columns (OSCs) and Geosynthetic Encased Stone Columns (GESCs). The improvement in capacity of both OSCs and GESCs is evaluated by performing California Bearing Ratio (CBR) test in laboratory by creating unit cell stone column models of different recycled aggregates and comparing their load settlement behavior with natural aggregates.Results and discussionRailway ballast, natural aggregates, concrete debris and virgin soil were found to show decreasing order in CBR test results. Loading required for causing settlement in both OSCs and GESCsshowed remarkable increase as compared to that of virgin clay and the maximum load settlement improvement was observed for railway ballast in both the types of stone columns. The CBR values for GESC made from railway ballast, natural aggregates and concrete debris were 54, 49 and 38% respectively. On the other hand, CBR for OSC made from railway ballast, concrete debris and natural aggregates were found to be 25.5, 20.4 and 24% respectively and CBR of virgin clay was found to be just 11%.ConclusionThe demonstrated application of sustainable sources in place of natural aggregates provides a crucial pathway for utilizing the recycled aggregates as stone column filler material. Up on encasing the OSC with geotextile the performance of stone columns has improved appreciably in terms of load capacity. Railway ballast and concrete debris can be adopted as an alternate for the natural stone column materials to improve the bearing capacity of site consisting mainly of soft clays.

Performance of stone columns in unsaturated soils: Numerical evaluation

Stone columns are often designed using the conventional framework of saturated soils, ignoring the influence of in-situ unsaturated soil conditions. Such an approach contributes to unrealistic and, in certain scenarios, over-conservative designs. The key objective of this paper is to quantify the influence of matric suction on the confining support offered by the surrounding soil towards stone columns. In addition, how this approach can be implemented through a numerical technique is also presented and discussed. The numerical analysis suggests that the load-carrying capacity of stone columns increased with an increase in the matric suction in the boundary effect, and the transition zone. However, the contribution of matric suction towards load-carrying capacity starts reducing from the residual zone of saturation. Furthermore, the performance of stone columns in unsaturated soils is strongly associated with the area replacement ratio. The results of the study are promising towards developing procedures that can be used in the rational design of stone columns in unsaturated soils.

Sensitivity of granular pile dimension parameters to deformation response of soft ground under building load

Granular pile is one of the proven soil improvement mechanisms applied especially for reinforcement of compressible soils supporting light structures. The improvement performance of granular piles is influenced by various factors including the dimension parameters (length, spacing and diameter of the piles). The influence of these three dimension parameters on deformation response of reinforced weak soil has widely been reported. However, the most influential parameter affecting deformation of the weak soil has not been clearly identified. Apparently, these dimension parameters do not equally influence the performance of stone columns in lessening soil deformation. Hence, comparative analysis was carried out in the current study to find out the dimension parameter to which deformation of stone column reinforced weak ground is most sensitive. Finite element based parametric numerical analysis was conducted to simulate the weak ground reinforced with a group of granular piles supporting light weight building. For the parametric study, five dimensions for each parameter (diameter, spacing and length) were considered. The dimensions were purposely varied by uniform percentage increase. Field settlement monitoring data was used to track deformation response of the site and validate the finite element results. The numerical analysis reveals that the simulation results have good agreement with the field settlement monitoring data. From sensitivity view point, column spacing was found to be the most controlling and influential parameter affecting deformation of the reinforced weak soil. Similarly, column length is the dimension parameter to which ground deformation is least sensitive.

Finite-difference solution for dissipation of excess pore water pressure within liquefied soil stabilized by stone columns with consideration of coupled radial-vertical seepage

The implementation of stone columns is a widely accepted method for improving the stability of liquefiable soil. A comprehensive understanding of the behavior of the composite ground is crucial for accurate design and calculation in practical applications. Several existing mathematical models were established to assess characteristics of the stone column-improved ground by typically ignoring the vertical seepage within liquefiable soil. This negligence will inevitably lead to significant calculation errors, particularly when the vertical permeability of liquefiable sites is high or the installation spacing of stone columns is large. In this context, a new mathematical model which accounts for coupled radial-vertical seepage within liquefiable soil is proposed to determine the reinforcement performance of stone columns. The equal strain assumption and new boundary conditions are incorporated to obtain numerical solutions with the finite difference method. Then the present solution is degenerated to the conventional calculation model to verify the reasonability of the proposed model. Finally, a parametric analysis is conducted to investigate the impacts of crucial parameters on the performance of stone columns for excess pore water pressure variation during soil liquefaction. The results reveal that the peak value of the maximum excess pore water pressure ratio increases with the increment of both the column spacing and cyclic stress ratio. Moreover, the increasing radial and vertical consolidation parameters Tb and Th will accelerate the dissipation rate of the excess pore water pressure of liquefiable sites. Furthermore, the conventional model neglecting the vertical seepage will underestimate the variation rate of the excess pore water pressure, and the calculation error will become larger with the increase of Th.

3-Dimensional Numerical Evaluation of Geosynthetic Encased Stone Columns in Unsaturated Soils

Geosynthetic encased stone columns are often designed using the conventional framework of saturated soils ignoring the influence of in-situ unsaturated soil conditions. This article evaluates the performance of stone columns with and without geosynthetic encasement extending the mechanics ofunsaturated soils. The focus of numerical simulations was directed towards understanding the influence of matric suction on the confining support offered by the surrounding soil to stone columns with and without geosynthetic encasement. Investigations were extended considering the stiffness and the length of the geosynthetic encasement. The numerical studies suggest the load-carrying capacity of stone columnincreased with an increase in the matric suction in the boundary effect and the primary transition zone. However, the contribution of matric suction towards load-carrying capacity starts reducing from the secondary transition zone. The information on boundary effect and transition zones can be derived fromthe soil-water characteristic curve, which is a relationship between the water content and soil suction. In addition, the effect of stiffness and length of encasing material in unsaturated soils was found to be in contrast with saturated soils. The results of the study are promising towards developing procedures thatcan be used in the rational design of stone columns in unsaturated soils.

Investigating the performance of stone columns in an extremely soft clay—A case study

SummaryStone columns are used to improve soft soils; however, they fail through bulging, punching, and lateral expansion when the soil is extremely soft. The present study investigated the performance of stone columns in an extremely soft clay (ESC) through the addition of the appropriate geosynthetic materials. Field test was conducted for the foremost purpose of obtaining the optimal spacing between the consecutive stone columns and therefore prevents the failures of stone columns in ESC soils. The study further examined the failure modes of stone columns for the case of ESC soils. The computer programming software FLAC 3D was used for modeling and simulation, while Auto CAD was used to draw needed geometries of the case study. The results revealed that the full encasement of the stone column with suitable geogrids, optimal spacing, and proper design of cushion will enable the efficient use of stone columns as a composite foundation in ESC. The considered appropriate thickness of the cushion was found to be 30 cm, and this cushion helps the embedded soft clay soils to work together with the installed encased stone columns in ESC soils. The center‐to‐center (optimal) spacing between two consecutive stone columns showed optimal performance at distance S ≤ 5d of the diameter of the stone column. These findings show that stone column encased with suitable geogrids and optimal spacing will improve the bearing capacity, reduce settlement, and decrease the lateral deflection as well as hoop strain of the foundation.

Performance of Stone Column in Soft Clay- Numerical Evaluation

Stone columns are an efficient ground improvement technique for treating problematic soils. The confidence in the prediction accuracy of bearing capacity remains unsatisfactory. Soil samples were collected from vellayani paddy field and basic laboratory experiments were done. This paper aims to investigate the bearing capacity of single stone column using three-dimensional numerical analysis. Failure modes were observed and the effect of key parameters such as column’s friction angle, undrained shear strength of surrounding soil and modular ratio were investigated. Numerical results showed bulging and a combination of bulging and punching are two dominant failure modes for the single stone column. Ultimate bearing capacity is mainly influenced by the column’s friction angle and the undrained shear strength of the surrounding soil. Based on the results, a new prediction method is developed and compared reasonably well with the existing analytical solution and the field measurements.

Evaluation Of Use of Stone Column in Unengineered Closed Landfill Soil

In the building industry, ground improvement techniques based on stone column are widely employed. It is a very successful approach for enhancing the engineering characteristics of soil in all aspects, as well as reducing the settling issue in poor-grounded soils including silt, clay, silty sand, and organic soil. The performance of stone columns, is determined by the confining pressure provided by the surrounding soils. Engineering constructions built on thick layers of soft soil strata face issues such as limited bearing capacity, excessive total and differential settlement, lateral spreading, and so on. To address such issues, many ground improvement techniques are available. In exceptionally soft soils, the lateral confining pressure may be inadequate, resulting in column bulging failure. Individual stone column encasement improves lateral resistance to bulging by adding restricting pressure. This research focuses on the geotechnical aspects of building on closed landfill sites. A total of 33 models were tested in a geotechnical engineering laboratory on virgin former landfill soil and stone column with and without encasement in this current study. The increased diameter, length and L/D ratio of the column has demonstrated that the load capacity has increased and soil settling has decreased. When an unreinforced stone column has been installed, the ultimate bearing capacity of landfill soil is increased by 75-112.50 per cent and 87.50-176 per cent respectively, for 10mm and 20mm diameter stone column. Furthermore, when a fully reinforced stone column has been installed, it had increased by 156.25-212.50 per cent and 200-298 per cent for 10mm and 20mm diameters respectively. The stiffness of soil is increased by the stone column, which contributes to increase in the load capacity. The geogrid layer confines an aggregate, which contribute to enhance shear stiffness and bearing capacity.

Utilization of stone column for improving seismic response of foundation on soft clay- Numerical study

Nowadays, some projects have to be constructed in areas having thick layers of soft clay. These soft soils with low shear strength and high voids ratio, lead to excessive settlements even if subjected to low vertical or lateral loads. For this reason, soft clays are considered problematic soils for foundation purposes. Several improvement techniques have been done to enhance such clay. Stone columns have been used to improve soft soils by increasing it carrying capacity and reducing the settlement. In this paper, a numerical study on seismic behavior of stone column in soft clay subjected to earthquake loading has been performed. A two-dimensional plane strain program PLAXIS (dynamic version) is used for the present numerical modeling. A series of modeled stone columns were simulated with different diameters and spacing between columns. Also, the influence of geotextile encasement on the performance of stone columns, foundation systems in soft clay is investigated and compared with the behavior of ordinary stone columns without casing. The results showed that the ordinary stone column with small spacing and larger diameter has a greater bearing capacity and give a smaller settlement, compared to the column with large spacing. In addition, the geotextile encasement for stone column can be provided a significant increase in stone column capacity as well as a huge reduction in settlement is considered with increasing the encasement strength.

Numerical investigation on the performance of stone columns under raft foundation in soft clayey soils

Stone columns are the most common and effective technique used for enhancing the overall strength and performance of soft soils. They are more effective for moderately lightweight structures. This investigation presents a parametric study of stone columns embedded in ground to strengthen the soft clayey soil under stiff raft foundation. This research is based on a computational analysis by creating a foundation finite element model consisting of a group of stone columns that are mounted under rafting using PLAXIS 3D. A certain range of parameters (for example spacing, diameter and angle of friction of stone columns) is considered and it is concluded that the increase in diameter and angle of friction of stone columns can improve the ultimate load bearing capacity of the foundation system. Furthermore, the failure mechanism of this foundation scheme is analysed and a semi-empirical model for the determination of the bearing capacity ratio (BCR) is developed from the results of the parametric analysis.

Influence of encasement length and geosynthetic stiffness on the performance of stone column: 3D DEM-FDM coupled numerical investigation

The design of geosynthetic encasement is the most important factor that controls the performance of the geosynthetic-encased stone column (GESC) improved ground, and encasement length (Lenc) and geosynthetic stiffness (J) are two basic design items. Numerous continuum-based numerical models have been proposed to investigate the influence of geosynthetic encasement on the behavior of GESC improved ground, however, the micro-mechanics of stone aggregates cannot be properly simulated due to its discrete nature. In this paper, a three-dimensional discrete element method (DEM) and the finite difference method (FDM) coupled numerical modeling scheme was proposed. Surrounding clay is modeled by the continuum method using FLAC3D and the stone column and geosynthetics are modeled by the discrete element method using PFC3D. The proposed numerical models are validated using laboratory observations. The influence of geosynthetic encasement is analyzed by predicting pressure-settlement behavior, lateral deformation of surrounding clay, stress distribution within the column, and microscopic characteristics of granular materials (i.e., porosity, coordination number and contact force distribution). Numerical results demonstrate that full length and high stiffness encasement will significantly improve the load-bearing capacity of GESCs. In practice, fully-encased stone columns are recommended for reducing the settlement.

Centrifuge modeling of geosynthetic-encased stone column-supported embankment over soft clay

Geosynthetic-encased stone column (GESC) has been proven as an effective alternative to reinforcing soft soils. In this paper, a series of centrifuge model tests were conducted to investigate the performance of GESC-supported embankment over soft clay by varying the stiffness of encasement material. The enhancement in the performance of stone columns encased with geosynthetic materials was quantified by comparing the test with ordinary stone columns (OSCs) under identical test conditions. The test results reveal that by encasing stone columns with geosynthetic material, a significant reduction in the ground settlement, relatively faster dissipation of excess pore pressure and enhanced stress concentration ratio was noticed. Moreover, with the increase in the encasement stiffness from 450 kN/m to 3300 kN/m, the stress concentration ratio increased from 4 to 6.5, which signifies the importance of encasement stiffness. In addition, a relatively lower value of soil arching ratio observed for GESCs compared to OSCs indicate the formation of a relatively strong soil arch in the GESC-supported embankment. Interestingly, under embankment loading, GESCs fail by bending while OSCs fail by bulging. The stress reduction method can be used to calculate the settlement of GESC-supported embankment with larger stress reduction factor than that in the OSC-supported embankment. Finally, the limitation of the construction of the embankment at 1 g was addressed.

LIGHTWEIGHT SLAG, PFA COLUMN A NEW SOFT GROUND IMPROVEMENT METHOD

This study investigates how to reduce the demand on in non-renewable granite source, by replacing granite aggregate with boiler slag in the stone column. It is a fact that boiler slag is a power station waste material which causes too many environmental problems. By introducing it as a ground improvement technique, we can reduce the bulging and shear failure problems encountered on stone columns application by adding more improvement to the stone column mixture. For more enhancements to the mixture, pulverized fly ash (PFA) of Class F is added. By increasing the amount of PFA, the resistance of the stone column in term of shear and bearing capacity are increased as the PFA pozzolanic reaction begins to produce more strength during the increasing time of the curing period. Both samples of the boiler slag and PFA are taken from Sultan Salahuddin Abdul Aziz Power Station, Klang, Selangor. The materials mixed are sand, cement and water to make boiler slag aggregates -PFA (slag) mixture. This study aims to define the slag concrete performance according to the optimum configuration of the materials used in the mixture. Unconfined Compression Test (UCT) is applied to define the ideal ratio of boiler slag between 60% to 30% ratios from the total weight which applied with 2% ratio of cement from the total weight. The results of the study show that the number of boiler slags, the period of curing, and the method of curing are the most important factors in defining the slag stone column performance. Testing the samples in ordinary circumstances to entire areas can be accomplished by determining the soil properties and meeting them. The best result gained was the 40% ratio of boiler slag in a curing method that preserved the mixture moisture and temperature, which led to the optimum strength of the slag stone column.

Assessment of Group of Stone Column Under Sesmic Condition

The study of group of stone column is concerned with evaluation and comparison of the behaviour of group of encased stone column and ordinary stone column for static and seismic load condition. Stone column system with specified geometry is modelled and analysed in FEM software program MIDAS GTS 3D. Analysis is categorised into four cases. Pseudostatic method is used for seismic load calculation. The objective of research is to analyse the performance of stone column by considering the effect of various parameters such as diameter of stone column, static and seismic load condition in cohesive clay and silty clay. Effect of encasement is also observed for static loading condition and seismic loading condition. Result shows that encased stone column reduces the settlement and length of stone column.

Experimental and numerical study on the bearing capacity of encased stone columns

Stone columns have attracted considerable attention as a ground improvement techniques recently. Performance of stone columns, however, depends on confining pressure offered by the surrounding soils. In the case of very soft soils, the lateral confining pressure may be insufficient and this may lead to column bulging failure. Encapsulating the individual stone column enhances the lateral resistance against bulging by additional confining pressure. In this study, the influences of the length of encasement and type of aggregate materials on the bearing capacity of a single stone column in both dry sand and clay bed were investigated. The results indicated a clear improvement by encasing the half-length of the column. The numerical study also showed the effect of reinforcement stiffness reduces with increase in the cohesion of the clay. Parametric study showed that the effect of encasement stiffness is insignificant for clay bed with high values of cohesion.

Laboratory investigation of the behavior of a geosynthetic encased stone column in sand under cyclic loading

This paper presents the results of a laboratory investigation into the behavior of a geosynthetic encased stone column (GESC) installed in sand under cyclic loading using a reduced-scale model. A number of test variables were considered, such as the geosynthetic encasement stiffness and the cyclic loading characteristics, including loading frequency and amplitude. The results indicate among other things that the overall benefit of the encasement to the performance of the stone column is greater under cyclic loading than under static loading. It is shown that the degree of load transfer to the column becomes smaller when subjected to cyclic loading than under static loading, leading to a 25% decreased stress concentration ratio. The encasement is found to be more effective in improving the stone column performance when subjected to lower frequency and/or smaller amplitude loading. The lateral bulging zone of the GESC under cyclic loading tends to extend beyond the reported critical encasement length for an isolated static loading case, and therefore full encasement is recommended. Practical implications of the findings are discussed in detail.

Assessment of the Performance of Stone Columns through the Seismic Wave Test: A Review

The geophysical testing is increasingly being employed in many geotechnical applications. It is preferred in monitoring the mechanical characteristics of the ground because of its economy, not time consuming and non-destructive nature. Seismic wave test is one of the geophysical methods which showed a potential in observing the general behaviour of the reinforced soil with stone columns. Findings in most cases showed that the seismic wave measurements was integrated with or compared to the conventional tests such as standard penetration test or cone penetration test. There was a noticeable success in identifying the enhancement achieved to the ground upon the strengthening with the column, specifically when the associated surveys can produce a clear image of the underground which interprets the variation in the soil properties not prior to the soil treatment only, but even after the treatment occurring. However, from practical point of view, there were still some restrictions with applying such a method, specifically relating to the extent of data gathered, technical concerns and the difficulty of measuring the waves or interpreting results with the presence of ground water. This paper summarizes the recent publication work concerning this technique with a key focus on advantages and limitations within this type of ground improvement.

Influence of Particle Gradation and Shape on the Performance of Stone Columns in Soft Clay

Abstract A stone column typically consists of particles whose influence has largely been overlooked in design practice in terms of stress transfer, pattern of deformation, and intrusion of fines (clogging). This article presents an experimental study on the load-deformation behavior of a model stone column installed in soft clay with a particular emphasis on the influence of particle gradation and shape under undrained loading. The results show that particle gradation and shape have a significant influence on the load-deformation behavior and the extent of fines intrusion into the stone columns. Relatively well-graded particle sizes favor the development of higher peak shear stresses accompanied by lateral bulging, whereas more uniform grading results in the development of distinct shear planes and smaller peak shear stresses. Deformed columns were also examined using computed tomography, and the porosity profiles at the end of the test were determined using micrographs. Maximum porosity typically occurred in the zone of extreme lateral deformation, with the results suggesting that the extent of fines intrusion was influenced by particle morphology.

Bearing Capacity of Strip Footing on Clay Slope Reinforced with Stone Columns

Bearing capacity is very important in geotechnical engineering, which depends on factors such as footing shape, stress distribution under footing and failure mechanism of soil. One of the methods for improving the bearing capacity and reducing settlement in soft and fine soils is adding column like elements to soil which called stone column. In this research using model tests and numerical modeling, the effect of existence and location of stone column on bearing capacity of strip footing near soft clay slope is studied. In fact, reinforced and unreinforced stone columns in different locations are added to slope and the effect of them on load-settlement behavior of strip footing rested on top of the slope was investigated. Group stone columns are also studied, and efficiency of them is investigated. Also numerical modeling is carried out with Plaxis 3D Foundation program, and finally the results of experimental and numerical modeling were compared. Results show that reinforcing clay slope with stone column in all situations leads to increase in bearing capacity of strip footing. Moreover, reinforcing stone columns with encasing cause better performance of stone columns and increase in bearing capacity of footing compared with the same unreinforced stone columns. The maximum effect of stone column on bearing capacity of strip footing occurs when the stone column is located beneath the footing, and with increase in distance between the column and footing, the bearing capacity of footing is decreased.