Three Dimensional Numerical Study on Behavior of Geosynthetic Encased Stone Column Placed in Soft Soil

Ordinary stone column (OSC) reinforced soft soils undergo excessive settlements under vertical stresses due to the lack of adequate lateral support from the surrounding native soil. To overcome this issue, stone columns are suitably encased by a geosynthetic material having high axial stiffness, which provides the required additional confinement. A numerical analysis aimed at analyzing the effect of geosynthetic encasement on the load settlement behavior of geosynthetic encased stone columns (GESC) under vertical stresses is presented. Three dimensional (3D) models were developed in PLAXIS3D to simulate the behavior of stone column reinforced soft soils using the unit cell idealization concept. The numerical models were first validated with the help of experimental data of model tests on GESCs from literature. Various parameters were varied to quantify their impact on the load settlement behavior under column only loaded condition. The parameters varied include the diameter of GESCs, spacing to diameter (S/D) ratio, pattern of stone column installation, geosynthetic encasement stiffness, length of encasement, length of floating column, cohesion of soil and friction angle of stone column infill. Increase in the diameter of GESCs led to increased settlement for a particular vertical load intensity. The bearing capacity improved with increase in the geosynthetic stiffness, encasement length, length of floating GESCs, the cohesion of soil and the friction angle of the stone column infill. Increase in S/D ratio decreased the bearing capacity and triangular pattern of stone column installation was found to be more efficient. Moreover, the lateral bulging indicated a reducing trend upon increasing the axial stiffness of encasement.