f Critical porosity, elastic bounds, and seismic velocities in rocks

Data for cornpressional Vp and shear Vs velocities versus porosity in sands show that none of the existing models are adequate predictors of velocities over the entire range of porosity: The Voigt and Reuss average are too far apart and too far from the data. Although self-consistent approximations for spherical pores and especially needles come closer to the data, they rail to account Ior the critical porosity Фc = 38% below which grains are load-bearing and above which grains are in suspension.