Modelling seasonal ratcheting and progressive failure in clay slopes: A validation

Seasonal wetting and drying stress cycles can lead to long-term deterioration of high-plasticity clay slopes through the accumulation of outward and downward deformations leading to plastic strain accumulation, progressive failure and first-time failures due to seasonal ratcheting. Using recent advances in hydro-mechanical coupling for the numerical modelling of unsaturated soil behaviour and development of nonlocal strain-softening regulatory models to reduce mesh dependency of localisation problems, the mechanism of seasonal ratcheting has been replicated within a numerical model. Hydrogeological and mechanical behaviours of the numerical model have been compared and validated against physical measurements of seasonal ratcheting from centrifuge experimentation. Following validation, the mechanism of seasonal ratcheting was explored in a parametric study investigating the role of stiffness and long-term behaviour of repeated stress cycling extrapolated to failure. Material stiffness has a controlling influence on the rate of strength deterioration for these slopes; the stiffer the material, the smaller the seasonal movement and therefore the more gradual the accumulation of irrecoverable strains and material softening. The validation presented provides confidence that the numerical modelling approach developed can capture near-surface behaviour of high-plasticity overconsolidated clay slopes subject to cyclic wetting and drying. The approach provides a tool to further investigate the effects of weather driven stress cycles and the implication of climate change on high-plasticity clay infrastructure slopes.