GROUND IMPROVEMENT BY DRIVEN IN«SITU GRANULAR PILES

Abstract

Because of rapid urbanization, requirement of suitable land for development of new city and industry have been increased in last two decade. Due to increased cost and many other environmental constrained of conventional foundation system encourage the geotechnical engineer in situ improvement of weak soil deposit. Improvement of marginal sites through installation of displacement type granular pile/stone column is one such method which has been successfully employed in many sites. In the present an experimental study has been conducted to examine the effect of installation of driven in situ stone column on loose sand bed. Prepared sand bed of low relative density was improved/densified by installation of displacement type granular pile. Loose sand just below the footing was improved by installing driven in situ stone column/granular pile. Plate load tests was conducted on loose sand bed and also after installation of stone columns just below the footing to determine the affect of installation of the driven in situ stone column. Loose sand below and surrounding the footing was improved by installation of displacement type sand piles. Plate load test were conducted to show the effect of improving the surrounding soil of the footing. Two types of material sand itself and gravelly sand were used as stone column material. Comparison has also been made between the two types of materials used in stone column in term of load carrying capacity. An approach has been described to determine the ultimate bearing capacity of the stone column improved ground. Modified density of the sand bed was calculated due to the installation of displacement type sand pile assuming no heave of the ground during. installation of the ground. Direct shear test was conducted of the sand bed preparing the sample at modified density to determine the angle of shearing resistance of the sand bed. Shear strength parameter of the stone column material have been found by preparing sample at the same density as is achieved in the stone column construction and then conducting direct shear test. Composite strength parameter of the improved ground calculated and using Terzaghi's bearing factor ultimate bearing capacity of the improved ground computed for the tested condition and compared with the test results. A procedure also suggested determining the ultimate bearing capacity of the driven in situ stone column improved ground which is supported by the experimental result.