Elastic wave velocities in partially saturated Ottawa sand: Experimental results and modeling

A theoretical model is needed to predict the macroscopic mechanical propert ies of soil from the size, shape, and elastic properties of its constituent particles. To test one such model, we compared measured and calculated val ues of compressional and shear wave velocities in Ottawa sand. The sand was packed in a cylindrical tank approximate to 0.9 m in diameter and 0.9 m de ep. 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 rais ed, In the air-dry sand the velocities varied nonuniformly with depth, reac hing 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 dept h dependence was removed. At higher saturations, the velocities gradually d ecreased until the zero tension level was at the top of the sand. The nonun iform depth dependence in the dry sand has been attributed to the tank wall supporting part of the gravitational stress in the material. A modified Di gby (1981) model was found to adequately account for the results in the wet material, A lumped parameter combining the contacts per grain, size, and t he grain roughness was used to tit the data. In terms of the model, it is c oncluded that the water in the contacts between the grains had little effec t on the normal contact stiffness, but reduced the tangential contact stiff ness to zero.