BEHAVIOUR OF REINFORCED SAND BED RESTING ON STONE COLUMN IMPROVED SOFT CLAY

Abstract

The granular piles are being used to improve the soft soil with accelerating the rate of consolidation and reinforcing the soft ground by increase the overall stiffness of the soil. Due to stiffness difference between the stone column and surrounding soft soil, higher amount of load has been transferred through stone column. A sand bed has been placed over stone column-improved soft clay to provide free drainage for consolidation of soft clay. The use of sand bed over stone column-improved soft clay also improves the load carrying capacity as well as reduces the total and differential settlement. The inclusion of reinforcement into the sand bed further improves the load carrying capacity of the soil. The usual way of design of stone column depends on the laboratorial investigation on single stone column test as the behaviour of single stone column is almost similar to the group of stone columns. The present dissertation deals with the behaviour of single stone column surrounded by soft clay. Laboratory model tests have been conducted to study the behaviour of stone column under different conditions such as circular footing directly placed on stone column and surrounding soil, unreinforced and geogrid-reinforced sand bed placed over stone column- improved soft clay. The improvement in load carrying capacity achieved under different conditions with reference to initial unimproved insitu soft clay has been observed and recorded. The influence of the depth of unreinforced as well as reinforced sand bed and size of geogrid on the performance of stone column-improved soft clay bed has been investigated through model tests. Due to the placement of unreinforced and reinforced sand bed over stone column-improved soft clay bed significant improvement in load carrying capacity of the soil has been observed. The bulging diameter has been reduced and the depth of bulging has been increased due to placement of reinforced and unreinforced sand bed. The optimum thickness of the unreinforced and georid-reinforced sand bed is found to be 0.6 and 0.3 times the diameter of the footing, respectively. The optimum diameter of the georid reinforcement is 3 times the diameter of footing. Numerical analysis has been carried out in three-dimensional explicit finite-difference program FLAC3D. The comparison between the numerical and experimental results shows reasonably good agreement.