Elastic Wave Velocities in Partially Saturated Ottawa Sand

A theoretical model is needed to predict the macroscopic mechanical properties of soil from the size, shape, and elastic properties of its constituent particles. To test one such model, we compared measured and calculated values of compressional and shear wave velocities in Ottawa sand. The sand was packed in a cylindrical tank ≈0.9 m in diameter and 0.9 m deep. The velocities were measured in the horizontal direction as a function of depth as the zero tension level of the water in the sand was slowly raised. In the air‐dry sand the velocities varied nonuniformly with depth, reaching a maximum value about two‐thirds of the way to the bottom of the tank. When water was introduced into the bottom of the sand, the nonuniform depth dependence was removed. At higher saturations, the velocities gradually decreased until the zero tension level was at the top of the sand. The nonuniform depth dependence in the dry sand has been attributed to the tank wall supporting part of the gravitational stress in the material. A modified Digby (1981) model was found to adequately account for the results in the wet material. A lumped parameter combining the contacts per grain, size, and the grain roughness was used to fit the data. In terms of the model, it is concluded that the water in the contacts between the grains had little effect on the normal contact stiffness, but reduced the tangential contact stiffness to zero.