Encased Stone Columns Research Articles

Behavior of floating stone columns reinforced with geogrid encasement in model tests

The bearing capacity and deformation characteristics of floating stone columns were complicated and are not thoroughly understood. In the present study, a series of experimental model tests of floating stone columns under vertical plate loading was performed. This study investigated the influence of geogrid encasement on the behavior of floating stone columns and provided valuable insight into the load-displacement behavior, bulging deformation, load transfer mechanism, and the radial stress of the geogrid encasement. The test results show that the bearing capacity of the floating stone column was significantly improved due to the geogrid encasement. The column with longer encasement showed higher stiffness at large settlements. The bulging deformation pattern of the column changed with different encasement lengths. More vertical pressure transferred from the top of the column to the bottom of the column due to the existence of the geogrid encasement. The fully encased stone columns developed high radial stress and achieved effective confinement of the column. The bearing capacities of the floating-encased stone columns with different encasement lengths were controlled by bulging deformation instead of penetration failure, which gave confidence that the floating-encased stone columns were an effective method for field construction in extensive soft 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.

Time-Dependent Behavior of Embankment Resting on Soft clay Reinforced with Encased Stone Columns

In this study, the time-dependent behavior of embankment resting on soft clay reinforced with encased stone column (ESC) is examined numerically. A three-dimensional slice model of an embankment resting on reinforced soft clay was developed to examine the influence of the stiffness of encasement material, length of encasement, and floating ESC on the time-dependent response considering various design parameters like generation and dissipation of excess pore pressure, settlement of composite ground, column deformation, and effective stress experienced by columns and surrounding soils. This investigation reveals that the performance of embankment resting on soft clay reinforced with ESC is better than resting on unreinforced soft clay and soft clay reinforced with granular columns without encasement. Apart from strength enhancement, consolidation characteristics of composite ground were also significantly improved by encasing granular columns with geosynthetic material. Moreover, with the increase in the stiffness of encasement, length of ESC, and length of encasement a significant reduction in the generation of excess pore pressure and lateral deformation were noticed. Further, load transfer mechanism, failure pattern, and temporal variation of stress concentration ratio depend on the encasement stiffness, column length, and encasement length.

Performance of Soft Clay Reinforced with Encased Stone Column: A Systematic Review

Performance of Soft Clay Reinforced with Encased Stone Column: A Systematic Review

Three dimensional analyses of geocell reinforced encased stone column supported embankments on lithomargic clay

ABSTRACT Geocells are a superior form of reinforcement due to their cost-effectiveness and three-dimensional confining properties. However, numerical modeling of geocell is always challenging due to its three-dimensional honeycomb structure. The limitations of the equivalent composite approach (ECA) led to the recent development of full 3D numerical models, which consider geocell-infill material interaction. This paper discusses the time-dependent performance of geocell-reinforced encased stone column-supported embankment considering the actual 3D nature of geocells using the finite element program ABAQUS. Parametric studies were carried out to study the stress transfer mechanism, vertical deformation of the foundation soil, and stress-strain variation inside the geocell pockets. It is found from the analyses that with the provision of a geocell layer on top of Geosynthetic Encased Stone Columns (GESC), the stress concentration ratio improved by 47% at the end of consolidation compared to GESC alone. Also, an 80% reduction in foundation surface settlement is observed with geocell-sand mattresses. The geocell-sand mattress decreased the bulging of the stone columns, and almost 80% of the stone column bulging occurred by the end of the embankment construction. The proposed model’s numerical results show that the equivalent composite approach overestimated the stress concentration ratio and bearing capacity. The tensile stresses are non-uniformly distributed in the geocell pockets, and the maximum tensile force was mobilised at the geocell mid-height. Among the various geocell infill materials analysed, the aggregates were best suited considering the stress concentration ratio and vertical settlement. The numerical results supported the idea that encased stone columns with geocells at the embankment base can perform similarly to a geosynthetic reinforced piled embankment system, which is costlier but very efficient. When the modular ratio is more than 40, geocell-reinforced encased stone column-supported embankment is similar to GRPES.

Geosynthetic Encased Concrete Debris Stone Columns

Rapid urbanization has compelled the building industry to improve the soft soil grounds which otherwise are unsuitable for construction activities. Ground improvement helps achieve better performance by avoiding several problems like excessive settlements, large lateral flow of soft soil beneath the structures, and loss of global or local stability under operational loading conditions by modification of foundation soils. The growing quantities and types of waste materials, shortage of landfill spaces, and lack of natural earth materials highlight the urgency of finding innovative ways of recycling and reusing waste material additionally can reduce the demand for natural resources creating sustainable ecosystem. The aim of this experiment is to use crushed concrete debris (CCD) in soil stabilization. A series of experiments are to be carried out to develop an understanding on the performance of soft clay foundation beds reinforced using geosynthetic encased stone-concrete debris column. Model tests was conducted on clay reinforced with encased vertical columns filled with both CCD and aggregates. A comparative study is to be done and an assessment of ultimate bearing capacity of the composite ground is to be done. The column failure mechanism in the both the cases are to be carefully studied. Modal tests and later numerical analysis is done in PLAXIS 2D for analyzing the behavior of geosynthetic encased stone column stabilized clay bed numerically. Analyses were carried out using Mohr-Coulomb’s criterion. Lab conditions were simulated in PLAXIS for accurate comparison for same model tests.

Bearing behaviour of floating and end bearing encased stone columns with different encasement materials

Bearing behaviour of floating and end bearing encased stone columns with different encasement materials

Effect of basal reinforcement on performance of floating geosynthetic encased stone column-supported embankment

In this paper, two centrifuge modeling tests were performed to investigate the influence of basal reinforcement on the global performance of floating geosynthetic encased stone column (GESC)-supported embankments. Based on the centrifuge tests, a 3-dimensional (3D) numerical modeling was carried out to investigate the influence of basal reinforcement on the deformation behavior of the floating GESC-supported embankment. The centrifuge and numerical modeling results showed that the basal reinforcement reduced total and uneven settlement at the embankment crest and base significantly. Moreover, the inclusion of the basal reinforcement significantly reduced the lateral displacement on top of the column, preventing outward bending of the floating GESCs below the embankment toe. However, the basal reinforcement increased the lateral displacement at the bottom of columns.

Numerical and theoretical analysis of geosynthetic encased stone column composite foundation under cyclic loading

In this paper, a model of the composite foundation reinforced with geosynthetic encased stone columns was established using the discrete element method, and the characteristics of its action under cyclic loading were studied. The influence of the length and radius of the pile on the settlement of the composite foundation is analyzed. The deformation characteristics of the pile and the stress ratio of pile-soil are studied under different pile lengths and radius. Then, based on this, the analysis of the lateral deformation characteristics of the piles under cyclic loading, the calculation model of the geosynthetic encased pile composite foundation is established. The settlement calculation formula of the composite foundation is solved according to the deformation coordination relationship between the pile and soil, the equilibrium condition, and the boundary condition. The results show that the theoretical value is in good agreement with the simulation value, which verifies the rationality of the theoretical calculation formula.

Comparative Study of Existing Cement Fly Ash Gravel pile and Encased Stone Column Composite Foundation

The Cement Fly Ash and Gravel (CFG) Pile and Encased Stone Column (ESC) are the ground improvement techniques. The main object of the study is to the numerical analysis of the Both techniques pile group were used to support the Embankment with and without the geotextile both techniques composite foundation by the Finite Element method under static and dynamic load analysis. Numerical simulation has been carried out in Plaxis 3D. A case study from china’s highspeed embankment supported by CFG and ESC have investigated the load caring capacity by soil and pile. While the failure behaviors, settlement, excess pore pressure, and lateral behavior with variable embankment loading and number of geosynthetic effect moreover, the diameter of CFG piles and ESC at various locations in an embankment has been varied to study its influence on the load distribution among the CFG piles/ESC and lateral load displacement of the pile group. The results show that increasing the diameter of both techniques reduced the total settlement and differential settlement of embankment. It observed that the seismic load has a significant effect on the vertical and lateral displacement.

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.

Influence of positions of the geotextile on the load-settlement behaviour of circular footing resting on single stone column by 2D Plaxis software

Purpose: This study aims to study the load – settlement behaviour of circular footing rested on encased single stone column. Design/methodology/approach: The effect of vertical, horizontal and combined verticalhorizontal encasement of stone column on the load carrying capacity were examined numerically. The effect of stone column dimension (80 mm and 100 mm), length (400 mm and 500 mm), and spacing of reinforcement on the load carrying capacity and reinforcement ratio were assessed. Findings: The obtained results revealed that the load carrying capacity of geotextile encased stone columns are more than ordinary stone columns. For vertically encased stone columns as the diameter increases, the advantage of encasement decreases. Whereas, for horizontally encased stone column and combined vertical- horizontal encased stone column, the performance of encasement intensifies as the diameter of stone column increases. The improvement in the load carrying capacity of clay bed reinforced with combined verticalhorizontal encased stone columns are higher than vertical encased stone columns or horizontal encased stone column. The maximum performance of encasement was observed for VHESC1 of D = 80 mm. Research limitations/implications: For this study, the diameter of footing and stone column was kept same. The interface strength factor between stone column and clay bed was not considered. Practical implications: The encased stone column could be use improve the laod bearing capacity of weak soils. Originality/value: Many studies are available in literature regarding use of geosynthetic as vertical encasement and horizontal encasement of stone column. The study on combined effect of vertical and horizontal encasement of stone column on load carrying capacity of weak soil is very minimal. Keeping this in view, the present work was carried out.

Earthquake Response of Model Footings on Soft Clays Strengthened by Stone Columns

The objective of the present study is to understand the behavior of soft soil strengthened by stone columns under dynamic seismic load. Ordinary and encased stone columns were used under different conditions. The present study converges around the dynamic response of stone columns of lateral shaking, the interaction of soil frame for understanding settlement mechanisms and the prediction of dynamic load limitations of foundations in soft soils subjected to seismic load (during vibrations). The results of this research will provide the basis for assessing measures to reduce the severity of seismic hazards and the seismic design of foundation structures in soft soils. As a result, soil models will be tested on the shaking table to make seismic ground vibration under several conditions (frequencies, undrained shear strength of soft soil, for stone columns type both ordinary and encased stone columns). It was concluded that the values of horizontal displacement increase by increasing the loading frequency, as well as the horizontal displacement is faster and greater at 2 Hz than 0.5 and 1 Hz in all cases. The rate of horizontal displacement increases in models on the soil of undrained shear strength cu= 15 kPa is greater than that in undrained shear strength cu= 25 kPa because increasing the strength of the soft soil leads to greater resistance to deformation and a decrease in the level of horizontal displacement.

EXPERIMENTAL STUDY ON GROUND IMPROVEMENT WITH STONE COLUMNS

Ground improvement is an important requirement in today’s construction industry as land reclamation is becoming increasingly popular. Stone column method is one of the efficient and economical method and it is one of the soil stabilizing method that is used to increase the bearing capacity and decrease the settlement of soft soils. In this research paper the bearing capacity, settlement of stone columns and encased stone columns were analysed using a scaled model. Gunny bags are used as geo textile for stone column encasement. The results shown significant improvement in bearing capacity of soil using stone column, the efficiency of stone column is increased when encased with geotextile.

A large-scale shaking table model test for acceleration and deformation response of geosynthetic encased stone column composite ground

Effective mitigation of seismic-induced ground hazards requires an improved understanding of ground response in terms of earthquake wave propagation and ground deformation. Here, this paper examines the effects of geosynthetic-encased stone columns (ESCs) and ordinary stone columns (SCs) on the acceleration amplitude and frequency content responses of sand profiles, and the deformation of the ground using a large-scale shaking table model test. The model was excited by 15 shaking events including El Centro motion, Wenchuan Qingping motion and Kobe motion with peaks ranging from 0.1 to 0.9 g. The results indicate that the ESCs more significantly amplify surface accelerations compared to the SCs in the frequencies ranging from 10 to 17 Hz and from 2.5 to 9 Hz. The horizontal peak acceleration values in the ESCs composite ground are approximately twice those of the SCs composite ground. The acceleration response of the ground is influenced by the applied acceleration peak and frequency content, reinforced type, and structure. After the seismic excitation, the ESCs composite ground develops much narrower surface cracks distributed in a larger area compared to the SCs.

Critical length of encased stone columns

Encased stone columns are vertical inclusions in soft soils formed by gravel wrapped usually with a geotextile. Their critical length is the one where further lengthening of the column provides a negligible improvement and it is therefore not effective to build columns longer than it. This paper aims to obtain common values of the critical length using simplified two-dimensional axisymmetric and full three-dimensional finite element analyses. A uniform soft soil layer with a linear elastic perfectly plastic behaviour is considered for the sake of simplicity. For the studied cases, the critical column length is around 1.3–2.5 times the footing diameter for encased stone columns, and slightly lower for ordinary stone columns, namely around 1.1–1.9. The critical length of the encasement is found to be slightly lower than the critical column length. The value of the critical column length is related to the extent of plastic deformation and that may be used to decide the column length in the design phase without the need of parametric analyses. As a first approximation, a general value of the critical column length of 2 and 2.5 times the footing diameter may be considered for ordinary and encased stone columns, respectively.

Numerical Study on Behaviour of Encased Stone Columns with Partial Content of Shredded Tyre Chips in Soft Clay Bed

The utility of construction of stone columns in soft soil like clay, marine soil in coastal regions as a ground improvement technique is widely acknowledged. This study presents a numerical analysis of behaviour of ordinary and encased columns, made of various mix proportions of shredded tyre chips and stone aggregates, through Finite Element modelling (with Plaxis 3D software). It is observed that encased columns exhibited remarkable decrease in bulging with respect to ordinary columns. This was true even for columns composed of high proportion of tyre chips (50–100% by volume) owing to generation of higher hoop strain in such columns. The development of hoop strain increased the tensile strength of encasement and hence the column stiffness. The study illustrates the variation of maximum lateral deformation and the corresponding depth with the amount of tyre chips in the mix proportion forming the column. A decrease in bulging along with bulging at greater depths was observed in encased columns, the bulging was negligible for columns wherein the tyre content varied between 0 and 30% by volume. The settlement reduced remarkably with the construction of encased columns irrespective of the mix proportions composing the columns. The study concludes that partial replacement (30–70% by volume) of stone aggregates with shredded tyre chips in encased columns in soft soil is feasible with encasement of significant stiffness.

Maxwell model geotextile encased stone column in soft soil improvement

In the field of geotechnical – soft soil improvement, the mathematical model or mechanical model is one of the important input parameters for the design calculations or studies. The determination of the appropriateness of the models has a great influence on the accuracy results of design and calculation as well as the sustainable stability of soft ground after improvement. On the contrary, the selection of inadequate calculation models will lead to increased costs of soft soil improvement, possibly even leading to the destabilization of the work and causing immense loss of people and property. Recently, many projects major highway after construction design in use has not meet the requirements of the standard, leading to wasted money and time of individuals, organizations, and the state of post-treatment. Therefore, the research and application of using mathematical or mechanical models in accordance with the new soft soil improvement method will greatly help as well as add additional options for soft soil improvement in Vietnam. The soft soil deformation is not only related to load but also to load time. The change in stress and deformation of weak soil over time is called rheology, and in this study is the viscoelastic behavior. From the above reasons, we try to apply a generalized Maxwell model to explain the viscoelastic behavior of a soft soil. In particular, the time-dependent behavior of a viscoelastic soft soil was represented by using the Maxwell rheological model. The Matlab programming code helps to solve numerically all the equation of the mathematical exhibition of the generalized Maxwell model results. We acknowledge that the generalized Maxwell model is superior in demonstrating the time-dependent behavior of soft soil. The results probably show that this is one of the effective models to predict the behavior of soft soils in ground improvement with GEC.

Settlement of Geosynthetic Encased Stone Columns Liquefaction Condition in Box Culvert

When the box culvert system is placed on a sandy soil layer with a relatively low bearing capacity and is disposed to potential liquefaction, the soil layer must be repaired to avoid damages to the box culvert structure. The proposed method is Geosynthetic Encased Stone Columns (GESC) to increase the bearing capacity and anticipated the liquefaction potential. however, to meet the criteria for a stable and safe GESC soil improvement in liquefaction conditions, the value of the settlement must meet the requirements for the settlement permit limit. This research was conducted to determine the potential for liquefaction at the study location, to calculate the value of single and group settlements in liquefaction conditions and to analyze the stability of single and group settlements including safe or unsafe in liquefaction conditions. Analysis of liquefaction potential was analyzed based on SPT data using the Valera and Donovan method, and settlement analysis applied the Almeida and Alexiew method. The analysis shows that potential liquefaction due to an earthquake with a magnitude of 9.0 SR will be at a depth of 4 to 8 m. Single and group settlements (144 sets) with an installation distance of 1.2 m with a diameter of 0.4 m and at a depth of 10 m are 246.23 and 214.92 mm, respectively. The entire GESC system is considered to be in an unstable and unsafe condition against potential liquefaction and box culvert loading.

Performance enhancement of encased stone column with conductive natural geotextile under k0 stress condition

In this study, the performance of the stone column encased with conductive jute geotextile in improving the characteristics of soft clay under k0 stress condition was evaluated using a custom-designed large-scale consolidation test setup. The electrokinetic-encased stone column (e-ESC) was designed as a cathode, while mild steel rods were chosen as anodes, and by applying a voltage gradient of 0.1 V/mm between the electrodes, electrokinetic processes were initiated. The efficacy of using the e-ESC in improving the performance of soft clay was assessed by comparing the results with an ordinary stone column (OSC) and encased stone column (ESC) reinforced soft clay. The results from the study reveal that the inclusion of stiffer material like OSC and ESC in soft clay has significantly increased undrained shear strength and modulus of subgrade reaction of the composite ground with a reduction in settlement and compression index. Due to the application of the voltage gradient between the electrodes, the rate of consolidation settlement of composite ground has significantly increased when compared to the OSC/ESC case. Further, it was confirmed from the chemical and mineralogical analysis that the pH, chemical composition, mineral phases, and microfabric of soft clay were altered with the voltage gradient.