BEHAVIOUR OF GRANULAR PILES WITH AND WITHOUT CONFINEMENT

Abstract

Ground improvement techniques make 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 granular material which is stiffer than the weak soil. Thus, the equivalent stiffness of treated ground becomes higher than the 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 the rate of consolidation. It has been found that load shared by the granular piles is much higher than that of the surrounding soil. The present dissertation work deals with the behaviour of geosynthetic encased granular pile installed in c-cp soil bed which is surrounded by a skirt wall. Laboratory model tests have been conducted to study the effect of skirt wall by varying its length and diameter on the performance of gianular pile. Short term load tests were carried out as per the guidelines of FHWA (1983). It was concluded from the experimental investigations that, the effect of skirt wall after a diameter of five times of diameter of pile is nullified and the skirt wall gives maximum load carrying capacity at a length of four to six times the pile diameter. Numerical simulation studies have been carried out to predict the behavior of granular pile and the results were compared with the experimental ones. Simulation software used was FLAC3D which is a three dimensional explicit finite difference program. The basis for this program is the well established numerical formulation used to simulate the behavior of three dimensional structures built on soil or rock. The comparison between the numerical and experimental results shows reasonably good agreement.