Geotextile Encasement Research Articles

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.

Filtration Capability of Geotextile Encasement to Minimize the Clogging of Stone Column During Consolidation

Filtration Capability of Geotextile Encasement to Minimize the Clogging of Stone Column During Consolidation

Utilization of bottom ash waste as a granular column to enhance the lateral load capacity of soft kaolin clay soil.

Implementation of industrial wastes such as bottom ash in ground improvement can be cost-effective and environment-friendly. Ground improvement is an effective method of mitigation to improve problematic soils including soft kaolin clay soils as the problematic soils always expose to the severe settlements, low shear strength, immoderate plasticity, greater compressibility, dispersivity, bulging, erodibility, and susceptibility to climatic variables. Several studies conducted on the granular column using the bottom ash column. However, only a few studies have reported findings coherent with the statistical analysis. In this study, the lateral load capacity of bottom ash column-kaolin clay has been conducted. Coherently, the reinforced kaolin clay samples were tested via particle size distribution, Atterberg limit test, relative density, compaction test, permeability test, unconfined compression test, and unconsolidated undrained triaxial test with the single and group of encapsulated bottom ash columns with the geotextile encasement and a prediction model was developed. The effect of a number of columns, column diameter, column height, area replacement ratio, height penetration ratio, height-diameter column ratio, volume replacement ratio, and confining pressures on the shear strength of the single and group of encapsulated bottom ash columns have been investigated. The findings showed the effectiveness of using the bottom ash columns at various number of column, column diameter, column height, area replacement ratio, height penetration ratio, height-diameter column ratio, volume replacement ratio, and confining pressures can enhance the shear strength of the soil up to 77.00% at the optimal utilization of single encapsulated bottom ash column of 10-mm diameter and 80-mm height. Therefore, the study proved that the utilization of bottom ash waste as a granular column can significantly enhance the lateral load capacity of soft kaolin clay soil.

Evaluating the Effectiveness of Nonwoven Geotextile-Encased Cinder Gravel Column in Improving Load-Bearing and Deformation Characteristics of Soft Clay

Application of vertically installed columnar materials made of natural gravels or crushed aggregate is one of the commonly implemented practices to improve the performance of soft clay grounds under footing load. Alternative materials like cinder gravel also plays a reinforcing role when blended with soft clay. However, information on the precise extent to which a vertically installed cinder gravel column is effective in improving the properties of a clay foundation and its potential response to the permanently applied footing load has not been well documented in the literature. Hence, the current study specifically aimed at evaluating the effectiveness of geotextile-encased cinder gravel column in improving deformation and bearing capacity of soft clay ground. The experimental model which considered installation of a single geotextile-encased cinder gravel column into soft clay was considered. A cylindrical steel container was used in designing the experimental test. The container was filled with clay soil and the cinder gravel column was vertically installed through a replacement method. Finding of the study revealed that ultimate load-bearing capacity of the soft clay foundation after being reinforced with conventional cinder gravel was 1.85 times that of the untreated soft clay soil. The load-carrying capacity of the clay soil decreased with increment in diameter of the column whereas it is directly related to the volume replacement ratio. With regard to directional improvement, the vertical reinforcement performs better than the horizontal geotextile strips in cinder gravel column from bearing capacity improvement view point. In lessening settlement, however, application of horizontal geotextile discs at spacing ranging between half- and full-column diameter overweighs performance of the vertical encasement. In summary, application of geotextile encasement to the top 75% of the clay thickness is sufficient to come up with optimum improvement in bearing capacity and encasing the entire thickness is not necessarily required.

Vertical stability of geotextile-encased sand columns without and with surrounding soil

Use of geotextile encasement can enhance the axial capacity of individual sand columns by providing an additional confinement, hence reducing both the radial and axial deformations. In very weak soils, geotextile-encased sand columns (GESaCs) may buckle due to the lack of confinement offered by the surrounding soil. This paper focuses on the vertical stability of individual GESaCs of various diameters and lengths tested in air to demonstrate their performance in the extreme case where the surrounding soil offers no confinement, and in weak soil, which simulates the more likely case where such columns would be considered for use. Loose sand was selected to simulate the weak surrounding soil. Loading tests were conducted on individual GESaCs prepared in air and loose sand to investigate the load capacity, radial strain, and axial strain of columns. GESaCs of smaller diameters exhibited higher axial pressure capacities compared with those of larger diameters. GESaCs prepared in either air or loose sand delivered higher axial capacities at smaller length to diameter ratios. Columns in loose sand exhibited lower radial and axial strains as compared with those in air when the same pressure was applied on the top area of the column.

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.

Filtration performance of geotextile encasement to minimize the clogging of stone column during soil liquefaction

Stone columns, which are frequently employed to stabilize the liquefiable soil, are susceptible to accumulation of soil particles. The progressive accumulation of the soil particles causes clogging of the stone column which decreases its drainage capacity. The stone column can be encased with geotextile to sustain its long term drainage function. The encasement prevents the movement of the soil particles into the stone pores. In the present paper, a mathematical model is presented to assess the filtration performance of the geotextile encasement to prevent the clogging. The filtration capacity of the geotextile is related to its maximum pore size, porosity and soil characteristics. It is observed that the encased stone column dissipates the excess pore pressure at a faster rate compared to the stone column without encasement. The peak maximum excess pore water pressure (Umax) is not significantly affected due to selection of the opening size of the geotextiles for single earthquake. However, the opening size can significantly affect the peak Umax value for multiple earthquakes. Depending on the capture coefficient of the stone column, the clogging can be fully prevented for higher hydraulic gradient if geotextile with maximum opening size in between D10 to D5 is used as encasement.

Deep-Seated Slope Stability Analysis and Development of Simplistic FOS Evaluation Models for Stone Column-Supported Embankments

Inclusion of stone columns in the underlain soft soil is one of the most prominent methods for improving the stability of embankments. The stone columns are encased with a geosynthetic material to further enhance the stability. The influence of this partial replacement of weak foundation soil with stone columns on the performance of embankments needs to be quantified. In this study, performance of ordinary stone column (OSC) and geosynthetic-encased stone column (GESC)–supported embankments is carried out using a three-dimensional finite element programme (PLAXIS3D). A parametric study was conducted to quantify the influence of various factors viz. spacing to diameter ratio (S/D), stiffness of encasement, cohesion of soil, friction angle of stone column and friction angle of embankment on the factor of safety against deep-seated failure. The results show that encasing the stone columns enhances the stability of embankments. Decreasing the column spacing (S/D) enhances the stability, reduces the excess pore pressure development and average settlement. Increase in geotextile encasement stiffness, cohesion of underlain soft soil, friction angle of stone column and friction angle of embankment improves the performance of embankments and also reduces the average settlement of the ground under embankment. Results of the parametric study were used to develop two types of data-driven models viz. multiple linear regression (MLR) and artificial neural networks (ANN) to simplify the evaluation of the factor of safety (FOS) of embankments. Among the two approaches, ANNs were able to predict the factor of safety values more accurately.

Drained triaxial response of clay reinforced with sand columns

In ground-improvement applications involving stone columns in soft clays, the columns act as drains that facilitate partial drainage during practical load applications. Partial drainage could improve the short-term strength of the clay/column composite. The objective of this work was to bracket the range of loading conditions by investigating the fully drained response of clay/column composites through consolidated drained triaxial tests. The area replacement ratio, the column penetration ratio and the presence of geotextile encasement were varied in the testing programme. A maximum improvement of 69% was observed in the deviatoric stress for area replacement ratios of 31·7%. A comparison between identical drained and undrained tests indicated that the deviatoric stresses were higher in drained tests with the drained response representing an upper bound for the strength of the reinforced clay specimens. When the improvements observed in triaxial tests were compared with improvements witnessed in full-scale footing tests, the triaxial test results seemed to over predict the per cent improvement observed in the field bearing capacity.

3D discrete element simulation of a geotextile-encased stone column under uniaxial compression testing

The geotextile encased stone column has been numerically modeled with the DEM gravel specimen wrapped by the finite-element shell structure. The irregular shape and size distribution of gravels have been simulated according to the experimental data using the rigid block module in PFC. The geotextile encasement has been modeled using the geogrid elements in FLAC3D. The complete stress–strain behaviors of the geotextile encased stone column under the uniaxial compression are successfully predicted and show good agreement with experiments. The failure of the encased stone column is controlled by the geotextile encasement, which might be raptured due to the column expansion and stabbing from irregularly shaped gravels. Without considering the stress concentration effect, the continuum-based models overestimate the bearing capacity of the geotextile encased stone column.

Performance of encased single stone column in layered soil

Stone columns were found to be effective, economical and widely-used ground improvement technique in soft grounds. It is important to understand the behavior of stone columns when they are installed in layered soils. This paper presents results from a series of small scale laboratory model tests carried out in unit cell tank to investigate the behavior of floating and end bearing stone columns in layered soils with and without encasement, consisting of loose sand overlying a soft soil. Tests were conducted with loading only the stone column area to estimate the limiting axial capacity of stone column. Laboratory tests were carried out on a column of 10 cm diameter surrounded by layered soil. Test results indicated that the bearing capacity of layered soil has been improved in all cases of stone column applications. The non- encased floating stone columns gave better results than non-encased end bearing stone column. The inclusion of geotextile encasement resulted in further improvement of layered soil and the encased floating stone column had superior bearing capacity improvement.

Behavior of Geotextile-Encased Single Stone Column in Soft Soils

Stone columns have become a widely used method of increasing bearing capacity of soft soils. This study investigates floating stone columns with and without encasement in soft soils. Although the stone columns in single-layered soil have been studied extensively, stone columns constructed in a base of varying soil layers are not fully understood. In the present study, the behavior of both single-layered soft soil and layered soil consisting of loose sand overlaying the soft soil was investigated by using small-scale laboratory pilot tests. The bearing capacity of soft soil was improved in all cases of stone column application. The contribution of stone columns on the bearing capacity of soft soil was presented by the term bearing improvement ratio (BIR). With a non-encased stone column in single-layered soft soil, the BIR was about 3.3-fold and with geotextile encasement in the same soil, the improvement ratio increased to 3.4-fold. For a non-encased stone column in layered soils, the BIR was about 2.0-fold and with geotextile enhancement in the same soil, this improvement ratio increased to 4.0-fold. The inclusion of geotextiles resulted in improved bearing capacity by distributing the induced stresses over larger areas. The maximum bulging of non-encased stone column in single-layered soft soil was observed at the depth of 1.5 times the original diameter of the stone column from the top, whereas for encased stone column in single-layered soft soil, the maximum bulging was transferred to a depth of 3.0 times the original diameter of the stone column.

Load-Settlement Response of Geotextile Encased Laterally Reinforced Granular Piles in Expansive Soil Under Compression

Expansive soils are prone to volumetric changes when interacted with water, which makes them unfavorable in civil engineers’ perspective. Granular piles are the effective and economic ground improvement techniques available under such criteria. As granular piles attain their support from surrounding soil, these generally fail by bulging under compression in soft clays. This limitation can be answered by provision of tubular geotextile encasement around the column. However, when the compressive loads are high, the bulging in granular pile makes the geotextile reach its tensile strength and does not provide any additional improvement. Further, this problem can be solved by providing lateral reinforcement in the column, as it tends to reduce the stress concentration at the top portion of the pile where bulging occurs, improving their performance. The present study deals with the response of granular piles in the presence of encasement and combination of encasement and lateral reinforcement under strain-restricted compression tests. In both floating and end-bearing granular piles, the load capacity of composite soil is substantially increased. The rate of increase in load-carrying capacity was higher when end-bearing granular pile was reinforced with geotextile encasement and minimal with additional lateral reinforcement. The results show that geotextile encased laterally reinforced granular piles of end-bearing type and floating type showed a substantial increase in load-carrying capacity relative to clay by 2.44 and 2.01 times, respectively.

Effect of granular piles with geotextile encasement on strength tests of expansive clays

This paper presents experimental data on unconfined compressive strength (UCS) and California bearing ratio (CBR) tests of expansive clay reinforced with granular piles (GPs) with and without geotextile encasement. One set of test samples were compacted at optimum moisture content and maximum dry density and were centrally reinforced with GPs of varying diameters and lengths. In another series of tests, the GP reinforcement was encased with a tensile geotextile. Both UCS and CBR test results increased with increasing length and diameter of the GPs. The test values further increased when the GPs were provided with geotextile encasement.

Behavior of sand columns reinforced by vertical geotextile encasement and horizontal geotextile layers

In this paper, the effect of a group of sand columns in the loose soil bed using triaxial tests was studied. To investigate the effect of geotextile reinforcement type on the bearing capacity of these sand columns, Vertical encased sand columns (VESCs) and horizontally reinforced sand columns (HRSCs) were used. Number of sixteen independent triaxial tests and finite element simulation were performed on specimens with a diameter of 100 mm and a height of 200 mm. Specimens were reinforced by either a single sand column or three sand columns with the same area replacement ratio (16%) to evaluate the Influence of the column arrangement. Effect the number of sand columns, the length of vertical encasement and the number of horizontal reinforcing layers were investigated, in terms of bearing capacity improvement and economy. The results indicated that the ultimate bearing capacity of the samples with three ordinary sand columns (OSCs) is eventually about 11% more than samples with an OSC. Also, comparison of the column reinforcing modes showed that four horizontal layers of geotextile achieved similar performance to a vertical encasement geotextile at the 50% of the column height, from the viewpoint of strength improvement, while from the viewpoint of economy, the geotextile needed for encasing the single column is around 2.5 times of the geotextile required for four layers.

Triaxial compressive behaviour of geotextile encased stone columns

A series of large-scale triaxial tests were performed on stone columns with and without geotextile encasement. Sixteen stone columns encased in four types of geotextiles and four ordinary stone columns with the size of 300 mm in diameter and 600 mm in height were tested under the confining pressures of 50, 100, 150 and 200 kPa. The results showed that the inclusion of geotextile encasement can be considered as a contribution to apparent cohesion or confining pressure of ordinary stone columns. The stress-strain relationship of encased stone columns was described as the superposition of a hyperbolic and a linear model, which were used to model the behaviour of triaxially loaded ordinary stone column and uniaxially loaded encased stone columns respectively. The model well captured the pre-failure behaviour of the encased stone columns.

Effect of Geotextile Encasement on the Shear Strength Behavior of Stone Column-Treated Wet Clays

The behavior of clay beds treated with ordinary and geosynthetic-encased stone columns under vertical loads is wisely well known. Since soil movements occurring in the field conditions may cause shear deformations in the stone columns, investigating the shear behavior of clay beds treated with stone columns is necessary. Also, a wide range of clays on the ground are wet (unsaturated) or dry in place, so this paper aims to experimentally investigate the shear strength parameters of untreated and treated wet clays by ordinary and encased stone columns by performing a series of large direct shear tests. For this purpose, the effect of some variables such as tensile stiffness and length of the encasement, frictional angle and size of column’s aggregates, diameter, number and arrangement of stone columns on shear strength parameters of such soils under various normal pressures are evaluated. The obtained results show a significant improvement in the shear strength behavior of the wet clay treated by stone columns due to geotextile encasement, but the rate of this improvement depends on physical and strength properties of stone columns and encasement.

Three-dimensional numerical analysis of individual geotextile-encased sand columns with surrounding loose sand

Use of geotextile-encased sand columns (GESC) to improve weak soils is an emerging technology that has great promise for field applications. This paper contains the results of a numerical study with the goal of quantifying the benefits of geotextile encasement under different conditions. A three-dimensional finite difference method implemented in FLAC3D 5.01 was used to evaluate the performance of a vertically loaded individual GESC installed in loose sand. The numerical model was first verified using the results of experimental tests performed on 150-mm diameter GESC installed in loose sand. The influence of various parameters was investigated in this study, including GESC diameter and length, soil thickness, geotextile encasement length, geotextile stiffness, and friction angle and dilation angle of the infill material. The results of the numerical model showed that vertically loaded GESC of smaller diameter experienced less settlement and lateral expansion than those of larger diameter. The geotextile material with higher stiffness had a substantial influence on the performance of GESC. The maximum effective geotextile encasement length depended on the load on the column head or the compressibility of the column.

Bearing capacity of soft soil model treated with end-bearing bottom ash columns

Granular column technique is a soil improvement method used to increase the bearing capacity of a soft soil area by replacing the soil with a group of granular column materials. The by-product utilisation is a worldwide interest for sustainable infrastructure development. Bottom ash, which is a combustion deposit derived from coal burning, is a potential by-product that could be used alternatively to sand or aggregate as a green granular column material. This research is to study the potential use of the bottom ash column-improved soft clay by conducting a series of small-scale physical modelling test. The bearing capacity behaviour and failure mode of soft clay improved with end-bearing group of bottom ash columns with and without geotextile encasement are investigated. The bearing capacity of soft clay is significantly enhanced by the inclusion of bottom ash columns; that is, 239% of bearing capacity improvement is observed with only 13% of improvement area. The bulging of the bottom ash column is transferred to buckling failure with higher bearing capacity when the bottom ash column is encased by geotextile. The outcome of this research leads to the usage of bottom ash by-product as a granular column material in sustainable soil improvement technique.