Geogrid Encased Stone Column Research Articles

Comparative Study on the Reinforced Sand-Bed and the Stone Column in Improving the Clay Deposit Supporting Isolated Footing

The working mechanism of a geotechnical structure can be understood from the deformations and the vertical stresses in the soil media. This article attempts to study the deformation, vertical stress development, and distribution of improved clay deposits carrying a single isolated footing. Through PLAXIS 3D software, numerical analyses were conducted for the ground improvement methods, such as the geogrid reinforced sand-bed (GRSB) and ordinary and geogrid encased stone column installation (OSC and GESC). In GRSB, the results show that the stresses were maximum at the sand–clay interface at a depth of 0.67 B (B—footing width). It is proposed to place an additional layer of geogrid at the interface, and it must be within the critical depth, i.e., the width of the footing. Furthermore, for the current study, the stiffness of the geogrid in the sand layer greater than 500 kN/m was insignificant in soil improvement, whereas the optimum axial stiffness of the stone column encasement was 1,000 kN/m based on the stress concentration factor. The stone column installation improved the clay layer even below the depth of 0.67 B, improving the capacity of clay to carry higher vertical stresses on par with the stone columns. The GRSB carried higher vertical stresses than the unimproved ground. However, the OSC and GESC could carry vertical stresses higher than the GRSB. This knowledge can allow the practitioners to decide the depth of placement of the reinforcement and also to choose an alternate if one method is not feasible for the site.

Numerical Analysis on the Behavior of Floating Geogrid-Encased Stone Column Improved Foundation

The ordinary (OSC) and geosynthetic-encased stone column (ESC) with different bearing strata significantly influenced its behavior. The paper established seven models for studying the behavior of floating stone columns using the finite difference method (FDM). The effect of geogrid and column length on the load-settlement behavior, bulging deformation, failure mode, and load transfer coefficient were also analyzed based on proposal models. The results showed that the bearing capacity of F-OSCs and F-ESCs increased with the increase in column and encasement length, respectively, and a critical length (i.e., 4D, where D was the column diameter) was found in settlement improvement. The bulging deformation was significant in F-OSCs and was observed at the top of a long column and the full length of a short column. The geogrid encasement could constrain the OSC to decrease the bulging deformation. The failure mode in F-OSCs was mainly a punching failure with bulging deformation for a short column (e.g., less than 4D), and was relative to the vertical pressure for a long column. The failure mode in F-ESCs was a punching failure, and the punching degree increased with an increase in encasement length. The load transfer coefficient of F-OSCs or F-ESCs was relatively stable as the column length increased to a critical value (e.g., 4D) or the encasement length increased to a critical value (e.g., 4D).

Prediction of the Bearing Capacity of Composite Grounds Made of Geogrid-Reinforced Sand over Encased Stone Columns Floating in Soft Soil Using a White-Box Machine Learning Model

Stone columns have been extensively advocated as a traditional approach to increase the undrained bearing capacity and reduce the settlement of footings sitting on cohesive ground. However, due to the complex interaction between the soil and the stone columns, there currently needs to be a commonly acknowledged approach that can be used to precisely predict the undrained bearing capacity of the system. For this reason, the bearing capacity of a sandy bed reinforced with geogrid and sitting above a collection of geogrid-encased stone columns floating in soft clay was studied in this research. Using a white-box machine learning (ML) technique called Multivariate Polynomial Regression (MPR), this work aims to develop a model for predicting the bearing capacity of the referred foundation system. For this purpose, two hundred and forty-five experimental results were collected from the literature. In addition, the model was compared to two other ML models, namely, a black-box model known as Random Forest (RF) and a white-box ML model called Linear Regression (LR). In terms of R2 (coefficient of determination) and RMSE (Root Mean Absolute Error) values, the newly proposed model outperforms the two other referred models and demonstrates robust estimation capabilities. In addition, a parametric analysis was carried out to determine the contribution of each input variable and its relative significance on the output.

Study on Bearing Capacity and Failure Mode of Multi-Layer-Encased Geosynthetic-Encased Stone Column under Dynamic and Static Loading

The “method of overlap” replaces traditional welding to solve the problem of how the geosynthetic-encased stone column is limited by the welding frame during site construction, making the site construction simplified and economical, but its bearing mechanism is not clear. Therefore, the bearing mechanism and failure mode of the stone column was studied through the compression test of the multi-layer geosynthetic-encased stone column under dynamic and static loading. The research shows that the multi-layer encasement improves the modulus and lateral restraint of the stone column, which increases the stress transfer rate and reduces the damage degree of the stone column. The vertical ultimate bearing capacity increase in multi-layer geosynthetic-encased stone columns under dynamic and static loading is significantly different, and the difference can be up to 47.1%; the corresponding number of encasement layers should be selected according to the actual situation. The influence of the difference between dynamic and static loading on the location of the main radial strain of the stone column can be ignored, but the lateral restraint of the stone column under dynamic loading is weakened, the stress transfer rate is reduced, and the radial strain is reduced and more uniform along the stone column height. The vertical ultimate bearing capacity of the one- and two-layer geogrid-encased stone column under dynamic loading is lower than that of static loading. When treating soft foundations, the influence of traffic loads should be considered, and the bearing capacity of the geosynthetic-encased stone column should be appropriately increased in design value.

Model Testing of Encased Stone Column Composite Foundations under Traffic Loads

In soft soil foundations, geogrid encased stone column composite foundation technology has been widely applied and developed in recent years due to its efficient treatment. In this study, eight groups of laboratory model tests were performed in a large-scale testing tank to investigate the bearing mechanism and stress characteristics of the composite foundation of geogrid encased stone columns under traffic loads with different cyclic load ratios. The stress at the bottom of the stone column and settlement of the composite foundation were measured and analysed. The test results show that cyclic shearing will cause the rearrangement of the soil particles at the column-soil interface, which will cause changes in the face pressure and effective stress state of the column-soil boundary. The cyclic load has a substantial influence on the accumulation settlement of the composite foundation and the development of the lateral stress state of the column. Based on the test results, the development law of the cumulative settlement is summarized, and the change mechanism of the column stress state is analysed and discussed.

A Three-Section-Settlement Calculation Method for Composite Foundation Reinforced by Geogrid-Encased Stone Columns

The analysis of the bearing characteristics and deformation mechanism of composite foundation reinforced with geogrid-encased stone columns is presented in order to obtain its settlement calculation method. The settlement of composite foundation is divided into three sections which are the reinforced section, unreinforced section, and underlying stratum. Based on Hooke’s law of space problem and the thoughts of the layer-wise summation method, the relative slip displacement between pile and soil of reinforced section without plastic zone is analyzed. The settlement of reinforced section is calculated by the layered iteration method based on the pile element model. The compatibility of vertical and radial deformations of unreinforced section is analyzed based on the pile-soil element model. The settlement of underlying stratum is still calculated by the layer-wise summation method. Finally, two engineering examples are analyzed and the results show that the settlement calculated by the presented method is close to the measured one. The method overcomes the defect that the calculated results by the other existing methods are more dangerous and it is more feasible and can be applied in engineering practice.

3D DEM-FDM Coupled Analysis of the Behavior of an Isolated Geogrid-Encased Stone Column under Axial Loading

AbstractThe axial loading test on a geogrid-encased stone column has been simulated using 3D numerical model in the proposed study. The stone column was modeled using the discrete element method (D...

Large-Scale Experimental Study on Collapsible Soil Improvement Using Encased Stone Columns

The aim of this study was to improve the characteristics of natural collapsible soils using the geogrid-encased stone column technique. For this purpose, 20 large-scale specimens of stone columns were prepared using rigid metal cylinders with a diameter of 308 mm and a height of 97 to 154 mm according to the unit cell theory. The aspect ratio was 10% to 25%. For the occurrence of bulging failure, the height of the stone columns was considered six times the diameter. The stone columns were encased with geogrids of varying stiffness from 80 to 200 kN/m. The soil around the stone column inside the unit cell was compacted to similar site conditions. Loading was applied similar to the test, which determines the soil collapsibility potential while the specimens were being inundated from the bottom of the metal cylinder by a water feeding system. During loading, the vertical displacements of the stone columns were measured at two locations on the loading plate. The results showed that the columns settlement due to inundation diminished by increasing the stiffness of the encased stone columns and aspect ratio. The optimum aspect ratio was approximately 15%. Encasement of the stone columns increased the lateral pressure in the collapsible soil and prevented the collapse of the stone column. The settlement values of stone columns were compared with a settlement prediction model and showed a good agreement. The data obtained in this study can be used as a practical method to improve natural collapsible soils during inundation.

Settlement Behaviour of Soft Soil Reinforced with Geogrid Encased Stone Column under Sustained Loading

The use of stone columns in improving the bearing capacity of soft soil is well researched, but the understanding of settlement requires further studies. This paper presents the results of a series of laboratory tests carried out to study the settlement behavior of soft soil bed reinforced with ordinary stone column (OSC) and Geogrid encased stone columns (GESC). Kaolin was used as the soft soil and stones of size from 2.5 to 10 mm were used as column material. The stone columns of four different diameters were installed, by the method of replacement, into the soil having undrained shear strength of 22.5 kPa. The OSC and GESC test beds were subjected to pressure of 250 and 300 kPa. Each pressure was sustained for 24 hours and the settlement of the composite soil with time was noted. It is found that Geogrid encased stone columns have small settlement than the corresponding ordinary stone columns. The SRR (settlement reduction ratio) being a measure of ground improvement, is found increasing with the area replacement ratio. Further, at a particular sustained pressure SRR is found more for GESC than the corresponding value for OSC.

Three-Dimensional DEM Analysis of Axially Loaded Geogrid-Encased Stone Column in Clay Bed

AbstractThe discrete-element method (DEM) was employed in this study to analyze the micromechanical behavior of an axially loaded geogrid-encased stone column (GESC) installed in a clay bed. A thre...

Effect of Column Configuration on the Performance of Encased Stone Columns with Basal Geogrid Installed in Lithomargic Clay

Lithomargic clay is extensively found along the Konkan belt in peninsular India and serves as a foundation for most of the structures. The reduction in strength under saturated conditions makes this soil problematic causing a lot of engineering problems such as uneven settlements, erosion, slope failures, and foundation problems. This paper presents the effect of column configuration (i.e. equivalent number of columns with reduced diameter for the same surface area) on the performance of lithomargic clay reinforced with geogrid encased stone columns and basal geogrid layer. The investigations were performed both experimentally through small-scale models and through finite element analyses. The results were compared with the performance of lithomargic clay reinforced with ordinary and encased stone columns. A single geogrid encased stone column with a basal geogrid layer improved the load-carrying capacity of lithomargic clay by 180% while the percentage of increment in the case of a group of three geogrid encased stone column with basal geogrid layer having the same surface area was 210%. It was also observed that the geogrid encasement of stone columns reduced the maximum column bulging by 38%, whereas geogrid encased stone columns along with basal geogrid layer reduced the bulging by 82% compared to ordinary stone columns.

A Study on the Behaviour of Stone Columns in a Layered Soil System

Stone columns are one of the cost-effective and efficient methods for improving the ground which strengthen the soil and reduce the settlements. The study of the behaviour of stone columns in layered soils is of great importance. In this paper, results obtained from the experiments done on the stone columns with varying thickness of clayey silt soil (lithomargic clay) at bottom and the lateritic soil at the top are discussed. The lateritic layers are varied from top for a depth of 1D to 5D where D is the stone column diameter. Experiments were performed on untreated soils alone, soil with the ordinary stone column, geogrid encased stone column with and without additional horizontal reinforcement called basal layer to geogrid encased stone column in lithomargic clay. Similar experiments were conducted using lateritic soil. By considering layered combination of these two soils, experiments were also performed on ordinary stone column, geogrid encased stone column and geogrid encased stone column with basal layer. Laboratory tests were conducted in a unit cell on the floating stone column of diameter 60 mm. The load capacity of the stone column and bulging characteristics are significantly affected with the increase in the layers of lateritic soil. The encasement of stone column enhances the stone column’s capacity and reduces the bulging. The additional horizontal reinforcement layer also showed a significant impact on the load capacity of the stone column. Experiments conducted were modelled and analysed using PLAXIS 2D software package.

Experimental and Numerical Investigation of Reinforced Sand Slope Using Geogird Encased Stone Column

Among all of the slope stability methods, use of stone columns and geosynthetic elements can be a good way for stabilizing. One of the efficient ways in order to reinforce earth slopes is Geogrid Encased Stone Column (GESC). This technique can dramatically increase bearing capacity and decrease settlement rate. The aim of this paper is experimentally to investigate a comparison between the behavior of Ordinary Stone Column (OSC) and GESC for reinforcing of sand slopes. The slope was constructed using raining technique and reinforced using GESC. The slope saturated through precipitation and loading procedure applied. The obtained results compared and verified with 3D Finite Difference Method (3DFDM). Both experimental and numerical analyses indicated that location of GESC in middle of the slope increases the bearing capacity of slope crown 2.17 times than OSC.

Behaviour of Geogrid Encased Stone Column in Pond Ash Fills

Behaviour of Geogrid Encased Stone Column in Pond Ash Fills

Behavior of foundation soil improved by stone column under cyclic load

This paper deals with using the stone column as a technique for the enhancement of the soft ground. The key goal of utilizing stone column is to decrease settlement and to increment the soil bearing ability, as well as decreasing the consolidation period. Nowadays, the current method concerns with various kinds of soil granular and cohesive. It is clear that the delicate soils (cohesive) possess a good settlement because of the disability of the ground to control the sidelong development and protruding of the stone sections. Moreover, the ways of utilization of the geosynthetic materials for encasement of the stone sections are other perfect ways to enhance the implementation, the quality, and firmness of stone segments. The present work investigates the behavior of the soft soil reinforced with ordinary and encased stone columns with geogrid under cyclic load. Six model tests were carried out on a soil with shear strength of about 15 kPa for both ordinary stone columns (OSC) and geogrid encased stone columns (ESC). For validating the enhanced method of utilizing stone columns, finite element model using the software PLAXIS 3D and field load exams had been applied. It was concluded that the models subjected to cyclic loading under the rate of loading 10 mm/sec reached the failure level faster than models tested under the rate of loading 5 mm/sec. The results of the finite element analyses of settlement compared with the records of settlement after the laboratory load tests seem to yield reasonably comparable values up to 50% of the design load. Afterwards, the recorded settlements show up to 60% higher values in compare with the results of the finite element analyses. This observation can be attributed to the occurrence of plastic failures under increasing load after an initial elastic response.

Three-Dimensional Discrete-Element Method Analysis of Stresses and Deformations of a Single Geogrid-Encased Stone Column

Three-Dimensional Discrete-Element Method Analysis of Stresses and Deformations of a Single Geogrid-Encased Stone Column

Three-dimensional DEM analysis of single geogrid-encased stone columns under unconfined compression: a parametric study

Three-dimensional discrete element method (DEM) was employed in this study to analyze the behavior of single geogrid-encased stone columns under unconfined compression. Four important parameters were investigated to understand and evaluate their effects on the behavior of the encased columns by seven DEM models. The biaxial geogrid used as an encasement material for stone columns was simulated using parallel-bonded particles, and the aggregate in the stone column was simulated using graded particles. Both the macroscopic responses (e.g., vertical pressure–strain curves) and the microscopic interactions (e.g., contact force, coordination number, and sliding fraction) of the columns under unconfined compression were analyzed and are presented in this paper. The numerical results show that the geogrid encasement with high tensile stiffness could provide high confining stresses and then effectively increased the bearing capacity of the column. The short column yielded quickly even though its column modulus at a small deformation was relatively high. The modulus of the column slightly decreased with an increase in the column diameter due to high circumferential strains mobilized in the geogrid encasement. The column with large aggregate was stiffer and deformed less than the column with small aggregate. Selecting aggregate with a size larger than the geogrid aperture size was an effective way to achieve better interlocking between the aggregate and the geogrid and to minimize mass loss for the geogrid-encased stone column under loading. Due to limited deformation allowed by the geogrid encasement, a coefficient of radial stress equal to half of the coefficient of passive earth pressure was suggested to estimate the ultimate bearing capacity of the geosynthetic-encased stone column.

Bearing capacity of footing supported by geogrid encased stone columns on soft soil

The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

BEARING CAPACITY and BULGING BEHAVIOR of GEOGRID ENCASED STONE COLUMNS

In recent years, geogrid encasement has been used to extend the utilization of stone columns to improve soft soil’s properties. This paper investigates the influence of geogrid encasement on the performance of stone columns in soft clay deposits. Experimental and numerical studies were conducted to figure out behavior of stone columns with and without geogrid reinforcement. The small scale laboratory tests were carried out. In addition, PLAXIS which is a finite element package intended for the two dimensional analysis of deformation and stability in geotechnical engineering was used to numerical studies. Before conducting the numerical studies, the validation between results of the experimental studies and numerical analysis was performed. After validation, the numerical studies were performed with different parameters such as the rigidity effect of geogrid, depth of geogrid reinforcement and lateral bulging of the stone columns. In addition, group of stone column was investigated. As a result of this studies, load carrying capacity and bulging behavior of the geogrid encased stone column was significantly influenced from the depth and the stiffness of the geogrid.

Effects of geogrid encasement on lateral and vertical deformations of stone columns in model tests

Geosynthetic encasement of individual stone columns can provide additional confinement to the columns thus increasing their load capacities and reducing lateral and vertical deformations. Most of past studies have been focused on the load capacities and settlements (i.e. vertical deformations) of the encased stone columns. However, the load transfer mechanism and the lateral bulging deformation pattern of the encased stone columns are not thoroughly understood. In the present study, four series of laboratory model tests in a large-scale testing tank were performed to investigate the effect of geogrid encasement on the lateral and vertical deformations of stone columns installed in a clay bed. For comparison purposes, ordinary stone columns were also tested and evaluated. The main objective of this research is to investigate the lateral and vertical deformation patterns of the encased stone columns and the reinforcement mechanisms of the geogrid encasement with different encasement lengths. In addition, the stress–strain characteristics of the encasement were measured and analysed. The test results show that the ultimate load capacity of the soft soil was greatly increased by the geogrid-encased stone columns. The effective length of the encasement was three to four times of the diameter of stone columns based on the consideration of performance and economy. In comparison with the analytical solution based on the unit cell concept with full encasement of columns, the experimental tests on composite foundations with partially encased columns, which allowed lateral deformations of columns and soils and slippage along the column-soil interfaces (geogrid–soil, stone column–geogrid, and stone column–soil if the column is not encased), resulted in larger settlements, especially at higher vertical pressures.