Stone columns (or granular piles) have proven to be ideal ground reinforcement for supporting flexible structures such as embankments and storage tanks. Stone columns installed in very soft soils will have very low lateral confinement: hence they undergo excessive bulging, leading to undue settlement and limited load-carrying capacity. In these situations, the strength and stiffness of the stone column can be enhanced by encasing the individual stone columns with a suitable geosynthetic. The encasement improves load transfer to deeper depths of soil. This paper investigates the qualitative and quantitative improvement of load capacity of individual encased stone columns through laboratory model tests. These tests were performed in a rigid unit cell that represents the stone column and the soil within the contributary area around the stone column. The load tests indicated a clear improvement in the load capacity of the stone column due to encasement. Encasement with geosynthetics having higher modulus resulted in stiffer response. The effect of encasement was found to decrease with increase in the diameter of the stone column. The improvement in the performance of stone columns was found to be significant, even with partial encasement. © 2007 Thomas Telford Ltd.

K Rajagopal

Department Of Civil Engineering

Clay

Columns (structural)

Flexible structures

Stiffness

Structural loads

GEOSYNTHETIC ENCASEMENT

Soft clays

STONE COLUMNS

Geosynthetic materials

COLUMN

Geosynthetics

GROUND SETTLEMENT

Model test

reinforced earth

Soft clay

SOIL IMPROVEMENT

soil reinforcement

LOADING (TESTING)

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Geosynthetics International

In urban areas scarcity of land to build infrastructure has driven the geotechnical engineers to improve poor subsoil conditions through different techniques. Granular column treatment is one of the most promising ground improvement techniques widely practiced all over the world. This paper discusses briefly the status of research on this topic. Focus is on the recent advancement of encasing these columns with geosynthetic products to enhance their performance in load bearing capacity and reducing the foundation settlements. This paper is divided into analytical, experimental, numerical and field studies on the aspect of encased granular columns (EGCs) which have been published in the past three decades. The primary objective of this study is to compile the above said aspects of EGCs into one single source of information to interested researchers in this field. Lot of studies have been conducted mainly on the laboratory aspects of EGCs. Very few attempts have been made by researchers to study the mechanism of granular columns at full-scale levels through field tests. Finally a brief summary with necessary discussions is provided on the efforts made so far in studying the behavior of EGCs. © Springer Nature Singapore Pte Ltd 2019.

Lecture Notes in Civil Engineering

A short review of geosynthetic granular column treatment of soft clay soils

The introduction of geosynthetics has drastically changed the manner of geotechnical practice. The challenges posed by the uncertainty of soil properties are easily overcome by the intelligent use of geosynthetics. The geosynthetics are applied practically in all areas of geotechnical engineering including the construction of steep slopes, retaining walls, ground improvement systems, landfills, drainage and filtration control around geotechnical structures, erosion control, etc. This lecture will briefly describe the history of geosynthetics and their applications to different infrastructure construction projects. The aspects of environmental sustainability that can be achieved through the use of geosynthetics are briefly brought out towards the end of the lecture. © 2016, Indian Geotechnical Society.

Indian Geotechnical Journal

The Geosynthetics for Sustainable Construction of Infrastructure Projects

A systematic series of slope stability analyseswere performed on embankments supported on soft clay soils treated with ordinary granular columns (OGCs) and geosynthetic encased granular columns (EGCs). The effect of various parameters such as the undrained shear strength of soft clay, friction angle of fill materials and aggregate in granular columns, area replacement ratio and the secant modulus of geosynthetic encasement on the factor of safety (FS) is analysed. A higher FS value is observed for EGC-supported embankments compared to embankments supported on OGC. In addition to full three dimensional (3D) modeling, an equivalent method is also presented in order to compare the solution accuracy and the relative computational efforts. The equivalent method yields similar FS values to 3D column models in the case of OGC, with lower computational costs. In the case of EGC, both methods give different FS values when the critical slip surface passes through the foundation soil, owing to the absence of the confinement effect provided by the geosynthetic in the equivalent method. For the same FS value, a significant reduction in area replacement ratio is observed when using geosynthetic encasement, which can reduce the consumption of natural resources. © 2017 Thomas Telford Ltd.

Undrained stability analysis of embankments supported on geosynthetic encased granular columns

In this paper, series of three-dimensional (3-d) numerical modeling of geosynthetic-encased granular columns were performed both in model and prototype scale using FLAC3D software to understand the lateral load carrying capacity of ordinary and geosynthetic encased granular columns (OGC and EGC). In the first part of the study, numerical modeling of direct shear tests were carried out. The soil in the direct shear box was reinforced with two different diameters of granular columns (50 mm and 100 mm) and three different patterns of arrangement (single, triangular and square) to study the effect of group confinement. The numerical simulations were carried out at four different confining pressures namely 15, 30, 45 and 75 kPa. From the numerical simulations it was observed that higher shear stresses are mobilized inside the granular column due to geosynthetic encasement and the magnitude of shear stress increases with increase in the normal pressure. It was found that the tensile forces in the geosynthetic encasement were mobilized both in circumferential and vertical directions, which helps in mobilizing additional confinement in the granular column. In the second part, the influence of the geosynthetic encasement of granular column treated soft ground was demonstrated through 3-dimensional slope stability analyses. © 2017 Elsevier Ltd

Geotextiles and Geomembranes

3-Dimensional numerical modeling of geosynthetic-encased granular columns

The behaviour of geosynthetic-encased granular columns (EGC) under vertical loads is reasonably well understood. To date, very little research has been done to understand the behaviour of EGCs subjected to lateral loads. The main objective of this paper is to quantify the effect of encasement on the lateral load capacity of EGCs. Several direct shear tests are performed on granular columns with and without encasement in a shear box having plan dimensions of 305 × 305 mm. Tests are conducted at different normal pressures varying from 15 kPa to 75 kPa. Two different diameters of columns, three types of encasements and three different plan configurations are studied in this research work. The results from these tests are discussed in terms of the increase in the shear strength due to geosynthetic encasement and the strength envelopes for understanding the influence of the encasement. Different types of failures observed in the granular columns (with and without encasement) subjected to lateral load are also discussed. © 2016 Elsevier Ltd.

Direct shear tests on geosynthetic-encased granular columns

Model tests on geosynthetic-encased stone columns

Stone columns (or granular piles) are increasingly being used for ground improvement, particularly for flexible structures such as road embankments, oil storage tanks, etc. When the stone columns are installed in extremely soft soils, the lateral confinement offered by the surrounding soil may not be adequate to form the stone column. Consequently, the stone columns installed in such soils will not be able to develop the required load-bearing capacity. In such soils, the required lateral confinement can be induced by encasing the stone columns with a suitable geosynthetic. The encasement, besides increasing the strength and stiffness of the stone column, prevents the lateral squeezing of stones when the column is installed even in extremely soft soils, thus enabling quicker and more economical installation. This paper investigates the qualitative and quantitative improvement in load capacity of the stone column by encasement through a comprehensive parametric study using the finite element analysis. It is found from the analyses that the encased stone columns have much higher load carrying capacities and undergo lesser compressions and lesser lateral bulging as compared to conventional stone columns. The results have shown that the lateral confining stresses developed in the stone columns are higher with encasement. The encasement at the top portion of the stone column up to twice the diameter of the column is found to be adequate in improving its load carrying capacity. As the stiffness of the encasement increases, the lateral stresses transferred to the surrounding soil are found to decrease. This phenomenon makes the load capacity of encased columns less dependent on the strength of the surrounding soil as compared to the ordinary stone columns. © 2006 Elsevier Ltd. All rights reserved.

Geosynthetic-encased stone columns: Numerical evaluation

Geomechanics and Geoengineering

Mechanical behaviour of geo-encased sand columns: small scale experimental tests and numerical modelling

Proceedings of the Institution of Civil Engineers - Ground Improvement

Discussion: Design of jet-grouting cut-offs

10.1680/gein.2008.15.issue-1

Journal	Geosynthetics International
ISSN	10726349
Open Access	No