Dynamic Properties of Sand–Fines Mixtures

Abstract

Dynamic properties namely shear modulus (G) and damping (h) are input parameters for predicting the ground response of natural soil deposits. The dynamic properties of sands and clays are dependent on many factors such as void ratio, confining pressure, strain amplitude, morphology, and plasticity characteristics. Considerable research has been reported in the recent past by Seed and Idriss (Soil moduli and damping factors for dynamic response analysis, 1970), Hardin and Drnevich (J Soil Mech Found Div ASCE 98(7):667–692, 1972); Seed and Idriss (Ground motions and soil liquefaction during earthquakes. Earthquake Engineering Research Institute, Berkeley 1982), Vucetic and Dobry (J Geotech Eng Div ASCE 117(1):89–107, 1991) and many others on dynamic properties of sands and clays. The factors affecting the dynamic properties of sands and clays are well documented, but soils generally, occur as mixtures of sand, silt and clay in various proportions. There is very little effort made in understanding the dynamic behavior of sand–fines mixtures and therefore there is a need to investigate the dynamic properties of sand–fines mixtures. In the present paper, the results of the behavior of sand–fines mixtures under cyclic loads are discussed. The experimental program consisted of a series of cyclic triaxial shear tests conducted as per ASTM D 3999 (Standard Test Methods for Determination of the Modulus and Damping properties of soils Using the cyclic Triaxial Apparatus. American Society for Testing and Materials 1991) to investigate the strain dependent shear modulus and damping of sand–fines mixtures of different plasticity. Sand was obtained from the Sabarmati river and three types of locally available fines i.e. low-plastic, medium- plastic and bentonite fines were used. Fines content was varied from 15 to 60%. The effect of fines content, plasticity, and relative density on shear modulus and damping is reported. Shear modulus at 0.005% strain level correlates well with the plasticity index for sand–fines mixtures of low to medium plasticity i.e. 0 < IP < 40.