Effect of plastic fines on initial shear modulus of sand-clay mixtures

This paper presents the dynamic properties of sand-fines mixtures based on the results of undrained cyclic triaxial tests. The sand was obtained from Sabarmati River, and three types of fines F1, F2, and F3 were obtained from locally available fine grained soils i.e. Black cotton soil, Suddha soil, and Bentonite soil. Sand-fines mixtures of wide range of plasticity from non-plastic to highly plastic mixture with PI = 86 were prepared using the fines passing 75 μ size. The initial shear moduli of all sand-fines mixtures are evaluated in terms of fines content, Plasticity Index (IP) and equivalent plasticity index (IP*) determined for soil passing 2 mm size IS Sieve. There is good correlation between the initial shear modulus of sand-fines mixtures and equivalent plasticity index (IP*) compared to Plasticity Index (IP). An empirical equation for obtaining initial shear modulus is formulated based on equivalent plasticity index and mean-effective stress.