STRENGTHENING OF CLAY BY GEOGRID REINFORCED GRANULAR PILE

Abstract

Ground improvement is a technique, which makes weak soil strata suitable to carry the expected load from the superstructure without failure and excessive settlement. Installation of granular piles is one of the methods of ground improvement technique in which a cylindrical hole is formed by scooping out the soil and replacing it by uncemented sand, which is stiffer than the weak soil. Thus, the equivalent stiffness of treated ground becomes higher than that of untreated ground. The beneficial effect of granular piles installed in weak deposits is manifested in the form of increased load carrying capacity, significant reduction in total and differential settlements and accelerating rate of consolidation. Use of granular pile also helps in improvement of slope stability of embankments. It has been found that load shared by the granular piles is much higher than that of the surrounding clay. In the present work, laboratory tests have been conducted to study the behaviour of granular pile installed in clay bed, reinforced with geogrid layers and supporting a rigid circular footing. Short term load tests were carried out as per the guidelines of FHWA (1983). The influence of depth and spacing of reinforcement on the performance of reinforced pile has been investigated through model tests. Model test were also conducted to determine the effect of length of pile and sand pad thickness on the load carrying capacity of reinforced granular pile. In order to determine the effect of consolidation of clay on the load carrying capacity long term test were also carried out. Tests were carried out on 50 mm diameter granular pile installed in clay bed. Geogrid reinforced granular pile results in significant increase in load carrying capacity and reduction in bulge diameter. Analysis of the test data have been carried out in FLAC3D which is a three dimensional explicit finite-difference program for engineering mechanics computation. The basis for this program is the well-established numerical formulation used to simulate the behavior of three-dimensional structures built of soil or rock. Comparison of numerical analyses has been carried out with the experimental results. Results from relevant published literatures have also been compared in order to validate the general findings from the present study.