Geotechnical Investigation of Black Cotton Soils

Black cotton soils for the study were derived from Indrasagar Rockfill Dam, Polavaram, Andhra Pradesh (India) from a depth of 1m, 1.2 m and 1.5 meters.Physical and geotechnical properties of the soil samples were studied in the laboratory.The tests conducted were grain size analysis, specific gravity, atterberg's limits, standard Proctor compaction, consolidation and direct shear test.Results as obtained were compared with the Indian standard code.Further, relationships of plasticity index with liquid Limit and optimum moisture content, compression index with liquid limit, optimum moisture content and plasticity index, angle of internal friction with plasticity index were also derived.The test results have shown that increase in the clay content in the black cotton soil attributes an increase in the plasticity index.Beside this, with the increase in optimum moisture content, an increase in the plasticity index, compression index, liquid limit were also observed.The study reveals that increase in the plasticity index induces decrease in the angle of internal friction.The empirical models with the help of regression analysis were also suggested for the benefit of field engineers for prediction of geotechnical properties of black cotton soil.