Unveiling the role of saturation and displacement rate in the transition from slow movement to catastrophic failure in landslides

Landslides commonly evolve from slow, progressive movements to sudden catastrophic failures, with saturation and displacement rates playing significant roles in this transition. In this paper, we investigate the influence of saturation, displacement rate, and normal stress on the residual shear strength and creep behaviour of shear-zone soils from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Results reveal a critical transition from rate-strengthening to rate-weakening behaviour with increasing displacement rates, significantly influenced by the degree of saturation. This transition governs the observed patterns of slow movement punctuated by periods of accelerated creep, highlighting the potential for exceeding critical displacement rates to trigger catastrophic failure. Furthermore, partially saturated soils exhibited higher residual strength and greater resistance to creep failure compared to nearly and fully saturated soils, underscoring the contribution of matric suction to shear strength.