John H. Schmertmann, Ph.D., P.E.
Professor Emeritus, Civil and Coastal Engineering, University of Florida
Given the great importance of horizontal stress, or the K ratio, in many geotechnical problems, it seemed reasonable that it might also have a great and previously unexpected importance in stress distribution. 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 experiment results with two elastic half-space theories will be compared: simple Boussinesq, nonhomogeneous Boussinesq, and one particulate-probabilistic theory described in Harr. A preliminary study with the PLAXIS finite element program will be presented to show promise for predicting both results. Practical applications and notes two principles of load transmission in soils demonstrated in the experiment will be discussed.