Small-Strain Stiffness, Shear-Wave Velocity, and Soil Compressibility

Abstract

The small-strain shear modulus depends on stress in uncemented soils. In effect, the shear-wave velocity, which is often used to calculate shear stiffness, follows a power equation with the mean effective stress in the polarization plane V-s = alpha(sigma(m)'/1 kPa)(beta), where the alpha factor is the velocity at 1 kPa, and the beta exponent captures the velocity sensitivity to the state of stress. The small-strain shear stiffness, or velocity, is a constant-fabric measurement at a given state of stress. However, parameters alpha and beta are determined by fitting the power equation to velocity measurements conducted at different effective stress levels, so changes in both contact stiffness and soil fabric are inherently involved. Therefore, the alpha and beta parameters should be linked to soil compressibility CC. Compiled experimental results show that the a factor decreases and the b exponent increases as soil compressibility CC increases, and there is a robust inverse relationship between alpha and beta for all sediments: beta approximate to 0: 73-0: 27 log[alpha/(m/s)]. Velocity data for a jointed rock mass show similar trends, including a power-type stress-dependent velocity and inverse correlation between alpha and beta; however, the alpha-beta trend for jointed rocks plots above the trend for soils.