Encased Stone Columns Research Articles

Numerical Stability Analysis of Sloped Geosynthetic Encased Stone Column Composite Foundation under Embankment Based on Equivalent Method

As an effective technology for the rapid treatment of soft-soil foundations, geosynthetic encased stone column (GESC) composite foundations are commonly used in various embankment engineerings, including those situated on sloped soft foundations. Nevertheless, there is still a scarcity of stability studies for sloped GESC composite foundations. Several 3D numerical models for sloped GESC composite foundations were established using an equivalent method. The influences of the area replacement ratio and the tensile strength of geosynthetic encasement on the stability were investigated. The results showed that the stability increased nonlinearly with the area replacement ratio, and there existed an optimal area replacement ratio (e.g., 24.56% in this study) to balance the safety and economic requirements. The stability increased linearly with the tensile strength of geosynthetic encasement at low tensile strength levels (lower than 105 kN/m in this study), and the impact was relatively limited compared with that of the area replacement ratio. In addition, the stability generally decreased nonlinearly as the foundation slope decreased, and high-angle (foundation slope close to 30°) sloped GESC composite foundations are recommended to be treated with multiple reinforcement techniques. The relationship between the minimum area replacement ratio and the foundation slope was further quantified by an exponential function, allowing for the determination of the area replacement ratio of various sloped GESC composite foundations and providing theoretical guidance for engineering practice.

Numerical Simulation of the Load Transfer Mechanism of a Geosynthetic Encased Stone Column Unit Cell under Embankment Loading

Numerical Simulation of the Load Transfer Mechanism of a Geosynthetic Encased Stone Column Unit Cell under Embankment Loading

Numerical simulation of bending characteristics of geosynthetic encased stone column

A numerical model of the cantilever bending structure of a geosynthetic encased stone column (GESC) of length 3 m and diameter 0.3 m was established using Z-Soil. The aim was to analyze the stress distribution and bending characteristics of the GESC under a bending load and to investigate the impact of encasement strength, encasement stiffness, gravel friction angle, and diameter on the bending characteristics of the GESC. The maximum bending moment of the GESC under bending conditions occurs at the anchored end. The dividing line of tensile and compressive stresses on the gravel in the anchored end section after bending failure appears at a radius of 0.5 of the column above the section centerline. The geosynthetic sleeve exhibits good resistance to tensile stress. The dividing line between the tensile and compressive stresses is located at the centerline of the section. The mechanical properties of the encasements and gravel has a significant impact on bending characteristics of the GESC. Increasing the strength of the encasement and friction angle of the gravel may significantly improve the bending capacity of the GESC, whereas an increase in the stiffness of encasement and diameter of the column decreases the bending deformation of the GESC.

Optimizing ground improvement with encased stone columns: a 3D numerical analysis in very soft clay

Purpose This study aims to investigate the behavior of different types of stone columns, including the short and floating columns, as well as the ordinary and the geosynthetic encased stone columns (OSC and GESC). The effectiveness of the geosynthetic encasement and the impact of the installation using the lateral expansion method on the column performance is evaluated through a three-dimensional (3D) unit cell numerical analysis. Design/methodology/approach A full 3D numerical analysis is carried out using the explicit finite element code PLAXIS 3D to examine the installation influence on settlement reduction (ß), lateral displacement (Ux) and vertical displacement (Uz) relative to different values of lateral expansion of the column (0% to 15%). Findings The findings demonstrate the superior performance of GESC, particularly short columns outperforming floating counterparts. This enhanced performance is attributed to the combined effects of geosynthetic encasement and increased lateral expansion. Notably, these strategies contribute significantly to decreasing lateral displacement (Ux) at the column’s edge and reducing vertical displacement (Uz) under the rigid footing. Originality/value In contrast to previous studies that examined the installation effect of OSC contexts, this paper presents a comprehensive investigation into the effect of geosynthetic encasement and the installation effects using the lateral expansion method in very soft soil, using 3D numerical simulation. The study emphasizes the significance of the consideration of geosynthetic encasement and lateral expansion of the column during the design process to enhance column performance.

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.

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.

Experimental investigations on reliquefication resistance of saturated ground reinforced with ordinary and encased stone columns

Experimental investigations on reliquefication resistance of saturated ground reinforced with ordinary and encased stone columns

Improvement of consolidation settlement beneath square footings using uncased and encased stone columns

Stone columns are considered a sustainable stabilization technique that has environmental compatibility and economic aspects to enhance the properties of soft soils below the overlying structures. This paper explores the effects of main related parameters on the consolidation settlement of square footing that rests over soft clay soil that treated using encased and unreinforced (uncased) stone columns. A Finite element modeling is established using PLAXIS 3D Software and was verified by previous experimental data. An extensive parametric study is performed numerically using various stone column parameters such as different replacement area ratios (Ar), numbers, lengths, properties, and geotextile lengths to determine the strain–stress behavior of stone columns. The developed finite element models found that the stone column area ratio (Ar) reduces both the settlements beneath the foundation and excess pore water pressure by 43% and 41%, respectively at Ar = 20%. Also, by increasing the penetrated depth and elastic modulus of stone columns, the settlement decreases significantly under footing. Conversely, there are slight effects of the stone columns number that have a constant area ratio on the foundation settlement. Furthermore, the optimal geotextile encasement length that reduces the settlement effectively was achieved when the encasement height ratio was half of the stone column height. Utilizing half-height encasement leads to cost savings, as it yields a 34% reduction in settlement from the uncased case while the settlement reduction achieved with full-height encasement was 44%.

Shaking table tests on the influence of geosynthetic encasement stiffness on the shear reinforcement effect of GESC composite foundation

This paper presents an experimental study of shaking table tests on two geosynthetic encased stone columns (GESC) composite foundation models with different geosynthetic encasement stiffness to investigate the influence of geosynthetic encasement stiffness on the shear reinforcement effect. The reduced-scale GESC composite foundation models were designed according to the similitude relationships by scaling the model geometry, geosynthetic encasement stiffness, and input motions for shaking table tests in a 1 g gravitational field. The GESC composite foundation models were constructed using poorly graded sand, gravel, and geotextile encasement, and then were excited using a series of sinusoidal input motions with increasing peak acceleration. The acceleration amplification factors for the GESC composite foundation model with higher geosynthetic encasement stiffness are larger than those of the lower geosynthetic encasement stiffness model due to the increased stiffness of the composite foundation. The higher geosynthetic encasement stiffness composite foundation has smaller settlements and lateral displacements under the same input motions compared to the lower geosynthetic encasement stiffness composite foundation. The incremental geosynthetic encasement tensile strains increase with increasing input acceleration for both models. The longitudinal tensile effect of geosynthetic encasement plays an important role on the shear reinforcement mechanism of GESC.

Comparison of Encased Stone Column with Conventional Column for Varied Parameters through Experimental and Numerical Investigations

Installation of stone columns is a widely used stabilization method in improving the characteristics of soft clays. In this study, laboratory tests were conducted to understand the influence of column number, spacing and encasement on the load-carrying capacity of the modified soil. Unit cell concept is adopted for column diameters of 25.4 and 31.75 mm, one and two numbers of columns and spacings of 50, 70, and 90 mm under the conditions of with and without encasement. In addition to the laboratory study, finite element analysis was also done for similar parameters to understand the modified soil’s settlement characteristics and stress concentration ratio. Based on the analysis, it is understood that the load-carrying capacity increases with number of columns and spacing. Considering the influence of encasement, larger diameter columns showed a more significant increase in the load-carrying capacity when compared to the smaller diameter columns.

Ground Improvement by Stone Columns: A Review

Abstract: Stone columns serve to improve the load-bearing capacity of loose soils in an environmentally sustainable as well as cost- effective manner. The review investigates the mechanical performance of encased stone columns compared to traditional ones and highlights the role of geosynthetics in enhancing their ability to bear loads and increase their stiffness. It is also explored the obstacles related to the installation of stone columns, encompassing possible construction complexities, compatibility with the prevailing site conditions, and the impact of groundwater on their effectiveness. Consideration of the stone column in terms of the deformation modulus for settlement analysis might reflect its behavior more accurately and realistically. This review provides a comprehensive assessment of stone column advancements, including current analytical, experimental, and numerical, and a study is carried out of their compressive, uplift, and seismic responses. Based on prior study findings, mathematical analysis, physical simulation, and comprehensive investigation, many aspects that impact the overall effectiveness of this approach have been identified

Horizontally Layered and Vertically Encased Geosynthetic Reinforced Stone Column: An Experimental Analysis

Because of the smaller confinement of the neighbouring soil in very weak soils, the carrying capacity of stone columns may not substantially increase. Geosynthetics can be used to reinforce columns by employing vertical encasement or horizontal layers. In the present study, large-scale laboratory investigations were carried out to evaluate the efficacy of vertical encasement and horizontal layering geosynthetics on the performance behaviour of soft clay. A series of tests were carried out for a horizontal layering of a geotextile with an equal distance throughout the height of the column (the total height of the column is ‘L’); horizontal layering over only the top half (i.e., 0.5 L from the head of the considered column); and horizontal layering over only the bottom half of the column (0.5 L from the centre to the foot of the column). Tests were also carried out for vertical encasement in the form of vertically encased stone columns (VESCs) that were employed for various lengths of encasement (i.e., L, 0.75 L, 0.5 L, 0.25 L). The tests were conducted for three different diameters of stone columns, i.e., 50 mm, 75 mm, and 100 mm. As per the findings, the utilisation of horizontal and vertical reinforcing layers enhances the carrying capability of stone columns. Moreover, because of their interlocking and frictional actions with the aggregates of stone columns, the layering decreases the lateral bulging of the considered stone columns. A comparison was performed to find the effectiveness of the horizontal and vertical types of reinforcement, and it was observed that VESCs with full-length encasement and a geotextile with a higher tensile strength for a 100 mm diameter of the stone column were the most desirable arrangements among all.

A Literature Review of Factors Affecting the Behavior of Encased Stone Columns

A Literature Review of Factors Affecting the Behavior of Encased Stone Columns

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.

Contribution of geosynthetic to the shear strength of geosynthetic encased stone columns

This paper presents a numerical study to evaluate the contribution of geosynthetic to the shear strength of geosynthetic encased stone column (GESC) under direct shear loading conditions. The backfill soil was characterised using the linearly elastic–plastic Mohr–Coulomb model. The geosynthetic encasement was simulated using linearly elastic liner elements. The interaction between the geosynthetic encasement and soils on both sides was modelled through two interfaces. The three-dimensional numerical model was validated using experimental data from direct shear tests of GESC models. The shear stress–strain response and the development of longitudinal and circumferential strains of GESC during the shear process were first discussed, and then a parametric study was conducted to investigate the effects of various design parameters on the shear strength of GESC and the contribution of geosynthetic. Results indicate that the shear resistance provided by the geosynthetic encasement develops slowly, which depends on the mobilisation of tensile strains. At the failure condition, the longitudinal strains are larger than the circumferential strains, which indicates that the longitudinal tensile rupture is more critical for GESC under shear loading. The vertical stress, geosynthetic encasement stiffness and stone column diameter and spacing have the most important influences on the shear strength contribution of geosynthetic encasement.

Geotechnical behavior of encased stone columns in soft clay soil

Geotechnical behavior of encased stone columns in soft clay soil

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.

Effect of micro-pile, stone column, and encased stone column mitigation on seismic performance of liquefiable ground in the coal-fired power station in Central Java

Liquefaction is a disaster that can damage building infrastructure. This disaster is all too common in granular sandy soils. This is due to the subsidence and instability of the soil when subjected to shocks such as earthquakes. For this reason, mitigation efforts are needed to reduce the risk of liquefaction. This study will compare the effectiveness and influence of micro-pile, stone column, and densification mitigation methods on granular soils at the Central Java PLTU site in reducing the impact of liquefaction risk on land, which is dominated by silty sand soil types. Each type of method has its own advantages in each type of supporting soil layer and has some differences in results due to differences in the material used even in the same dimensions. The purpose of this study was to assess the most suitable use for soil types in the area of the Coal-Fired Power Station in Central Java. This model was analyzed using OpenSees PL software, considering the shocks obtained from the 2007 Niigata earthquake at PEER NGA-WEST2 by analyzing factors such as displacement and reduction in excess pore pressure.

Behaviour of Encased Stone Columns in Soft Clay

Behaviour of Encased Stone Columns in Soft Clay

Numerical Study on the Deformation Behavior of Geosynthetic-Encased Stone Columns Supporting Embankments

The method of encasing the stone column with a proper type of geosynthetic material is a widely used technique to provide the required lateral confinement and to avoid the dispersion of granular column material into soft clay. Along with the improved ultimate load capacity and the reduced settlement and bulging, the geosynthetic encasement preserves the easy drainage ability of stone columns. This paper presents the finite element analysis results of a hypothetical embankment on a soft soil deposit which is improved by geotextile encased stone columns and geogrid reinforced sand mat on top. At first, numerical results of three dimensional (3D) finite element model (FEM) were validated via the experimental data of previous field studies. Afterward, parametric studies were carried out on the FEM considering the effect of the sand mat thickness, the stiffness of the geosynthetic reinforcement, and the geosynthetic encasing length and encasement stiffness on both the horizontal and vertical deformation of stone columns. Settlement differences between columns and soft soil in both the short term and long term were also determined. The optimum values of sand mat layer thickness, vertical encasement length, and geosynthetic stiffness are recommended to be used for preliminary designs.