Volume 34, Issue 4 (July 2011)
Centrifuge Test to Assess the Seismic Compression of Partially Saturated Sand Layers
A new testing approach for characterization of the response of partially saturated sand layers to cyclic loading is described in this paper. The approach involves basal shaking of a soil specimen within a laminar container using a hydraulic servo-controlled shake table in a geotechnical centrifuge. Infiltration of water was used to control the profiles of matric suction and degree of saturation, and thus the effective stress state, in the partially saturated sand layer during centrifugation. At steady state infiltration, relatively uniform profiles of degree of saturation and matric suction developed with depth in the sand layer. By varying the infiltration rate, different initial unsaturated conditions were obtained for cyclic testing. Instrumentation was incorporated into the setup to measure the accelerations induced in the shake table and soil profile, surface settlements, volumetric water content profiles, and pore water pressure. Cyclic tests were performed on sand layers having degrees of saturation ranging from 0.00 to 0.55 to assess the impact of effective stress on the layer’s deformation response. A nonlinear trend was observed in the variation of surface settlement with degree of saturation, with a minimum value obtained for sand having a degree of saturation of 0.28. This trend is consistent with the relationship between small strain shear modulus and degree of saturation for this sand.