Effect of Strength Anisotropy on Bearing Capacity of Shallow Footing in a Dense Sand

Abstract

Stress components in an anisotropic soil is analyzed on the assumption that it behaves like an anisotropic-rigid-plastic material. Numerical solutions by the stress characteristics indicate that the bearing capacity factor Nγ by self-weight is easily over-estimated about 40%∼50% when the effect of the strength anisotropy of sandy soils is neglected. The bearing capacity tests by means of a small testing box also support the possibility of the over-estimation. The ultimate bearing capacity is maximum when a strip footing is penetrated perpendicular to the bedding plane, while when a strip footing is penetrated parallel to the bedding plane, the bearing capacity becomes minimum. The ratio of the maximum to the minimum is 1.6 for dense Toyoura sand. In spite of the remarkable effect of the strength anisotropy on the bearing capacity, the residual bearing capacity is constant without any effect of the strength anisotropy. On the basis of the qualitative accordance between the experimental results and the anisotropic-rigid-plastic solutions taking account of the effect of the mean pressure, it can be said that the so-called scale effect of Nγ is mainly caused by the decrease of mobilized angle φ with the increase of the mean pressure.