Modelling retrogressive failure of quick clay using fully coupled flow-deformation SPH framework: the Gjerdrum (Norway) landslide case

Numerical modelling of retrogressive quick clay landslides is challenging due to their complex failure mechanism. Traditional undrained or total stress approaches that incorporate a strain-softening constitutive model for quick clay often suffer from mesh dependency and fail to properly account for the evolution of excess pore-water pressure, leaving the failure mechanism still not fully understood. This paper explores these challenges by employing a fully coupled flow-deformation SPH framework, integrated with a critical state CASM model, to investigate the retrogressive quick clay landslide that occurred in Gjerdrum, Norway, in 2020. CPTU test data are used to identify the soil type, stratigraphy and their constitutive parameters. These data are then incorporated into the SPH framework to simulate the retrogressive failure mechanism of the Gjerdrum landslide. This modelling explicitly captures the evolution of excess pore water pressure within the shear bands and its role in triggering strength softening behaviour. The proposed approach provides a detailed representation of the interaction between pore water dynamics and quick clay behaviour. The framework successfully reproduces field observations, demonstrating its capability to capture the dynamic interaction between pore water pressure, effective stress, and strength softening in sensitive clays.