Influence of Configuration of Stone Columns on Combined Footings Resting on Reinforced Earth Beds

Abstract

This work deals with the deformation analysis of combined footings resting on geosynthetic and stone column improved ground and subjected to symmetrically placed column loads. Simple mathematical model has been proposed which idealizes a combined footing as a beam. Just below the footing, there is the presence of a granular fill layer which has been modeled as a Pasternak shear layer. Geosynthetic layer, idealized as an elastic extensible membrane, has been placed in between this granular soil layer. There is an existence of a soft soil layer below geosynthetic-reinforced granular fill layer improved by stone columns. Stone columns and the soft soil layer have been represented by Winkler springs and Kelvin-Voigt body respectively. Nonlinear behavior of granular fill, stone columns and the soft soil has been considered in the analysis employing hyperbolic constitutive relationships. Governing differential equations have been derived and solution of these has been obtained with the help of appropriate boundary and continuity conditions. Finite difference method has been adopted for solving the model of footing-geosynthetic-reinforced granular fill-stone column reinforced soft soil system. Parametric study has been conducted to study the influence of configuration of stone columns. Five column loads have been considered. These results have been presented in the form of non-dimensional charts which can be used for deciding the optimum configuration of the stone columns in such soil-footing system. It has been seen that both these parameters, i.e., diameter and spacing of stone columns significantly influence the response of combined footing. The deflection of footing has been found to reduce with reduction in spacing to diameter ratio (s/d) of stone columns. The ratio, s/d has been found to possess an optimum value of 2.5–3.