Numerical study of the effect of geosynthetic encasement on the behaviour of granular columns

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Abstract
In very soft soils, the use of granular columns can be restricted due to the lack of adequate lateral confining pressure. In these conditions, the columns can be encased by a suitable geosynthetic to provide the required confining pressure and to increase their bearing capacity. Using a high-strength geosynthetic for confinement not only increases the strength of a granular column, but also prevents lateral displacement of the column into the very soft surrounding soil. This paper describes three-dimensional finite element analyses carried out to simulate the behaviour of a single granular column with and without encasement in a very soft clay using the computer program ABAQUS. Comprehensive numerical analyses were performed to study the influence of the geosynthetic stiffness, the friction and dilation angle of the column material, the length of geosynthetic encasement, the diameter of the column, the length of the column and the coefficient of in situ lateral earth pressure. Model results show that the stress–settlement behaviour of granular columns can be significantly improved by encasing them. The stiffness of the encasement was found to have a major effect on the stress–settlement response of encased columns and their associated load-carrying capacity. For partially encased columns, the optimum length of encasement was found to be a function of the stress that is applied to the column.

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