A PORE PRESSURE MODEL FOR CYCLIC STRAINING OF CLAY

Abstract

The paper focuses on the development and modelling of residual cyclic pore water pressure, u, in clay during undrained cyclic strain-controlled loading. Data obtained from a series of NGI type cyclic simple shear tests were employed. In addition to the amplitude of cyclic shear strain, γ_c, the number of cycles, N, and the overconsolidation ratio, OCR, a new component is incorporated in the conventional characterization of u. This new component is the volumetric threshold shear strain, γ_tv, of clayey soils, below which for all practical purposes u does not develop. The lack of understanding of complex clay microstructure and the associated interaction between clay particles during cyclic shearing makes the modelling of u in a manner other than curve fitting rather difficult. This is especially true in regard to the development of negative u in overconsolidated clays. A model based on the systematic curve fitting of the pore pressure data expressed in terms of γ_c, γ_tv, N and OCR is presented. The possibilities of the incorporation of such a model into existing numerical tools for simulation of the seismic and ocean wave loading response of natural soil deposits are briefly discussed as well.