Combined Encased Stone Column and Vacuum Consolidation Technique for Soft Clay Improvement

Abstract

Soft clay improvement using stone column is one of the popular ground improvement techniques adopted for soft clay deposits. The load carrying capacity can be further improved by encasing it with geosynthetic material around the column which offers effective lateral confinement, prevents column contamination with improved drainage and strength characteristics. The load carrying capacity can be further increased by improving the undrained shear strength of surrounding soil. Use of vacuum consolidation is a well-developed hydraulic modification technique which involves application of vacuum through prefabricated vertical drains in a sealed membrane system. The improvement in effective stress during vacuum application resulted in improved undrained shear strength of surrounding soil. In this research work, combined geosynthetic encased stone column and vacuum treatment method is examined for improving of extremely soft clay soils. Small scale unit cell tests were performed to evaluate the efficiency of encased stone column subjected vacuum loading under different pressure levels. The results were then compared with that of ordinary surcharge preloading conditions. It was observed that both time, rate of consolidation and undrained shear strength of soil increases significantly with vacuum application. With this reduction in time required for consolidation and improvement in undrained shear strength, the construction activity can be accelerated which makes the project economically beneficial.