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.

K Rajagopal

Department Of Civil Engineering

Sunil Ranjan Mohapatra

Geosynthetic materials

Direct shear test

Geosynthetics

GRANULAR COLUMNS

lateral loading

Soft clays

Testing

FAILURE ANALYSIS

granular medium

Loading

Shear strength

SHEAR TEST

Soft clay

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

Geotextiles and Geomembranes

In this paper, an attempt is made to analyse the dilative behaviour of dense sand at two different sizes of the direct shear box, i.e., small (60 mm × 60 mm ×30 mm) and large (305 mm × 305 mm × 140 mm). A three-dimensional numerical model is developed using the FLAC3D software to analyse the size effect on dilative behaviour of dense sand along the top and the shear plane of the box at 15 kPa normal pressure. It is observed that the vertical deformation of soil on top plane increases linearly with horizontal displacement, whereas on shear plane, the vertical deformation remains constant after yielding of sand. It is also found that there is greater movement of sand particles at the front and the back of the box for the large shear box compared with that for the small shear box. © Springer Nature Singapore Pte Ltd 2019.

Lecture Notes in Civil Engineering

Effect of box size on dilative behaviour of sand in direct shear test

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.

Geosynthetics International

Undrained stability analysis of embankments supported on geosynthetic encased granular columns

The stone columns (or granular piles) are increasingly being used as ground reinforcement elements for supporting a wide variety of structures including buildings and flexible structures. The stone columns derive their load capacity from the confinement offered by the surrounding soil. In very soft soils this lateral confinement may not be adequate and the formation of the stone column itself may be doubtful. Wrapping the individual stone columns with suitable geosynthetic is one of the ideal forms of improving the performance of stone columns. This type of encasement by geosynthetic makes the stone columns stiffer and stronger. In addition, encasement prevents the lateral squeezing of stones in to the surrounding clay soil and vice versa, preserves drainage function of the stone column and frictional properties of the aggregates. In spite of many advantages, the behavior and the mechanism of the geosynthetic encased stone columns is not thoroughly understood. This paper investigates the qualitative and quantitative improvement of individual load capacity of stone column by encasement through laboratory model tests conducted on stone columns installed in clay bed prepared in controlled condition in a large scale testing tank. The load tests were performed on single as well as group of stone columns with and without encasement. Tests were performed with different geosynthetics for the encasement of stone column. The results from the load tests indicated a clear improvement in the load capacity of the stone column due to encasement. The increase in the axial load capacity depends very much upon the modulus of the encasement and the diameter of the stone column. The increase in the stress concentration on the stone columns due to encasement was also measured in the tests. The results from the tests were used to develop the design guidelines for the design of geosynthetic encasement for the given load and settlement. © 2010 ASCE.

Journal of Geotechnical and Geoenvironmental Engineering

Studies on the behavior of single and group of geosynthetic encased stone columns

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.

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.

Journal	Data powered by TypesetGeotextiles and Geomembranes
Publisher	Data powered by TypesetElsevier Ltd
ISSN	02661144
Open Access	No