INFLUENCE OF STONE COLUMN ON STRENGTH AND CONSOLIDATION CHARACTERISTICS OF BLACK COTTON SOIL

Abstract

Black cotton soil (BCS) is a residual soil which is widely found in various regions of India and many other parts of the world. These soils are characterized by poor strength, high compressibility and low permeability and hence, provide a severe engineering threat. Black cotton soil extends in large stretches and construction of pavement and other infrastructures on such soils is a great problem, owing to their volume change characteristics. Hence to overcome these problems, stone columns are widely used as a ground improvement measure in black cotton soil. In the present study, the influence of stone column on the consolidation and strength behavior of black cotton soil is thoroughly studied. Laboratory tests are carried out on both end bearing and floating type stone columns, having diameter (d) 50mm, 60mm and 70mm with l/d ratios 3, 4 and 5 (l being the length of the stone column), installed in black cotton soils. The load-settlement and consolidation behavior of unreinforced and stone column reinforced black cotton soil are compared. It is seen that for d =50 mm and l/d =3 , the load carrying capacity increases by 20% and 48% for end bearing and floating type stone columns reinforced black cotton soils as compared to unreinforced black cotton soil. Moreover the void ratio (e), coefficient of compressibility (av), coefficient of volume change (mv), coefficient of consolidation (cv), coefficient of permeability (k) and compression index (cc) of black cotton soils are significantly affected by the l/d ratio and diameter of the stone column. Design charts and tables proposed in the present study reflects the efficiency of using stone columns as suitable ground improvement techniques in areas covered with black cotton soils.