A Semi-Analytical Framework to Simulate the Motion of Creeping Landslides

Landslide initiation, movement, and arrest are controlled by coupled hydro-mechanical processes. In this paper, a modeling framework solving the coupling between excess pore pressure dissipation and the landslide sliding dynamics is discussed. The model focuses on the basal shear zone, where inelastic deformation and displacement concentrate. The framework simulates the entire life cycle of a landslide, from triggering to runout, and enables a versatile incorporation of multiple inelastic constitutive laws. With these features, the framework can be used to capture different trends of landslide motion, from episodic events with velocity lower than 1 m/year to highly mobile runaway failures faster than 10 m/s. Here the framework is tested with perfect plastic frictional behavior. It is shown that closed form analytical solutions can be recovered. Notably, it can be shown that at steady state, a creeping landslide moving under the effect of sustained hydrologic forcing can be depicted as an equivalent damper with a viscosity dictated by the hydro-mechanical couplings in the shear zone. Specifically, our analyses show that triggering and propagation are dominated by a small number of characteristic timescales, including those controlling the time of consolidation, shear wave propagation, and viscous soil response. In the presence of dilation, negative excess pore pressure regulates the landslide mobility resulting in stable seasonal creep. By contrast, vanishing dilation (i.e., critical state) leads to sharp acceleration and large runout. In addition, for liquefiable soils (negative dilation), we show that small shear pulses can lead to self-feeding excess pore pressure buildup if the load is imposed faster than a critical rate. The satisfactory performance displayed by the model in simulating several case studies corroborates its versatility to support the interpretation of slope movement patterns and the assessment and mitigation of landslide hazards.