Bearing Capacity Improvement of Soft Silty Soil Bed by Stone Column

Abstract

The application of stone column is efficient ground improvement technique for soft silty soils. In very soft silty soil, the stone column undergoes excessive bulging, because of very low lateral confinement provided by the surrounding soil. The performance of stone column can be improved by using different sizes of stone, encapsulation of stone column by geogrid, geojute and geotextile material.
In the present study, a detailed experimental work has been carried out by performing plate load test on soft silty soil bed. The behaviours of single stone column and multiple stone columns in different pattern have been used. The effect of diameter of stone column, quarry dust in different percentage of quantity with 10mm and 20mm size of stone on the load carrying capacity have been analysed. Bearing capacity ratio, settlement reduction factor, percentage improvement in ultimate loading and percentage reduction in settlement has been reported.
It has been found from the experimental investigation, that the increased diameter of stone column is more effective and more efficient than the number of stone columns. 2 mm (quarry dust) size of stone is more efficient than the 10mm and 20mm size of stone. When geotextile is used as an encapsulation material to the stone column, it gives 80 % higher bearing capacity compared to geogrid encapsulation. The bearing capacity for geotextile encapsulation gives 30 % higher bearing capacity compared to Geojute. Thus, it is found that geotextile serves better purpose as encapsulating material compared to Geojute and Geogrid. The reason being that the tensile strength of Geotextile is much higher than that of Geojute and Geogrid. It has been found that triangular pattern both for 5 cm and 3 cm diameter of stone column gives almost same bearing capacity. Thus in triangular pattern, there is not much effect of stone column diameter. The matrix of 50% quarry dust and 10 mm size of stone is more efficient to improve the load carrying capacity than the 100% of 10mm size of stone. Due to encapsulation of stone column by Geotextile and Geogrid, the maximum reduction in settlement is 81.2 %.

As relative density of the stone columns increases, bearing capacity increases and at 90 % relative density, the increase in bearing capacity is 231.25 %. At 90% relative density of stone column, the settlement reduces by 300 %.