Pore-Water Pressure Buildup in Clean Sands Because of Cyclic Straining

The prediction of pore-water pressure buildup in sands caused by undrained cyclic loading is one of the key items in evaluating the potential for liquefaction of sandy sites during earthquakes. Presented herein are data indicating that, in strain-controlled tests, there is a predictable correlation between cyclic shear strain, number of cycles, and pore-water pressure buildup; this correlation is much less sensitive to factors, such as relative density and fabric than comparable results obtained from stress-controlled tests. Also, there is a threshold cyclic shear strain below which there is no sliding at the contacts between sand particles, and essentially no pore-water pressure buildup occurs. The data indicate that, for clean sands, this threshold shear strain, as well as the pore-water pressure buildup for strains slightly above the threshold, are basically independent of relative density, grain size distribution, fabric, and method of testing (triaxial and direct simple shear). However, both threshold shear strain and pore-water pressure buildup do depend on the overconsolidation ratio.