Pore Pressure Developed in Saturated Sand Subjected to Cyclic Shear Stress Under Partial-Drainage Conditions

Abstract

This paper presents the theoretical and experimental studies on the pore pressure developed in saturated sand subjected to cyclic shear stress under partially drained conditions. We analyzed pore pressure buildup obtained under partially drained conditions using the threedimensional consolidation equation. Though the rate of pore pressure buildup under undrained conditions has previously been used in this type of analysis (Seed et ah, 1976 and Sasaki et ah, 1982), the rate used in the present analysis was obtained from a series of cyclic triaxial tests carried out under partially drained conditions. Specifically, the pore pressure was decreased to a predetermined level of pore pressure which develops in the saturated sand specimen during each single shear stress cycle. The results of this analysis are useful in estimating the level of pore pressure which can develop, during an earthquake, in saturated sand deposits that have been treated using the gravel drain method. To examine the validity of the analysis, we performed liquefaction tests on saturated sand under partially drained conditions using the shaking table. The following conclusions were reached: The rate of pore pressure buildup under partially drained conditions uq' is significantly different from the rate of pore pressure buildup under undrained conditions, and it is related to the coefficient of pore pressure decrease denoted by ∆ u/ū, where ∆ u represents the amount of decrease of pore pressure and ū represents the pore pressure before the decrease occurs. Moreover, the calculated results of the pore pressure developed in saturated sand under partially drained conditions are in good agreement with the results obtained experimentally in the shaking table tests.