Improvement of Soft Clays Using Stone Columns with and Without Encasement

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AbstractEngineering structures constructed on thick deposits of soft clay have problems of low bearing capacity, excessive total and differential settlement etc. To mitigate such problems, stone column technique seems to be a very suitable and favorable ground improvement technique for deep soft soil improvement. Further to prevent excessive bulging and squeezing of stone into soft soil, stone column can be encased with suitable geo-synthetics. Another advantage of encasement is having high load-carrying capacity and lesser settlement of composite foundation. This paper presents an experimental study of single granular piles with and without encasement in improving the bearing capacity and reducing the settlements. The main objectives are (a) to identify key considerations for the general use of encased stone columns and columns without encasement and (b) provide insights for design and construction. Laboratory experiments have been carried out with granular piles of size 6 cm. In laboratory setup, hydraulic pressure was used to apply the load to the soil granular pile system and the dial gauges were used to measure the settlements. To obtain the stiffness of the pile, a test was carried on piles with and without encasement, by loading only the pile material neglecting the confining effect of the surrounding soil as the soil is soft in nature. Study of the bearing capacity ratio, defined as ratio of the bearing capacity of treated soil with granular pile to the bearing capacity of untreated soil for a given settlement for the foundation, was conducted. Granular piles are made of stone and sand, and encasement of piles with leno-netted material. To cast the piles, casing pipes of the required diameter 6 cm were used.KeywordsTiffnessModulus of elasticityStone columnEncasedBearing capacity