Stress Diffusion Experiment in Sand

Plate bearing load tests in a large sand box with boundary lateral stress control showed, by measurements using buried stress cells, that the greater the initial horizontal stress the more rapidly the vertical loading from the plate diffuses or spreads horizontally with depth. The measurements also showed that with horizontal stress constant, an increasing plate load progressively focuses a greater percent of the load into the sand under and along the axis of the plate. These diffusion and focusing results have the same cause and can become linked. The paper compares the experiment results with two elastic half-space theories: simple Boussinesq, nonhomogeneous Boussinesq, and one particulate-probabilistic theory described in Harr. Only Harr predicted the first results qualitatively. None predict the second results. A preliminary study with the PLAXIS finite element program shows promise for predicting both results. The paper also discusses practical applications and notes two principles of load transmission in soils demonstrated in the experiment.