Insights into void ratio redistribution during undrained monotonic shearing of Malaysian kaolin

This article experimentally and numerically evaluates the void ratio redistribution observed during undrained monotonic shearing of Malaysian kaolin at different loading rates. On the one hand, undrained monotonic triaxial tests were performed on normally consolidated samples of Malaysian kaolin. In these tests, the void ratio was measured in different sections of the sample before and after the undrained monotonic shearing stage. On the other hand, fully coupled three-dimensional numerical simulations were conducted using an anisotropic hypoplastic model for clays. The experimental and numerical results revealed that, although there was obviously no variation in the global void ratio during undrained monotonic shearing, a redistribution of void ratio was observed within the samples, remarkable at all loading rates investigated. Numerical simulations also revealed significant pore water pressure inhomogeneity, which, however, decreased with decreasing loading rates. The rigid end platens further imposed significant inhomogeneity of total stress state within the samples. The reasons for these observations are thoroughly analysed and discussed throughout the article. The results show that assumptions adopted in calibrations of constitutive models using single element tests (constant volume and homogeneous stress and pore water pressure distribution) do not adequately reproduce the more complex reality.