LAUSR

When the safety factor of natural or artificial slopes reaches critical value of 1.0, the increment of triggering factors, i.e. precipitation, rise of groundwater level, earthquake, and slope interference may prompt slope failure. Considering the impacts and damages possibly caused by rapid landslides, it is important to predict its runout distance, velocity, moving volume, and coverage area. A numerical model was developed to calculate the rapid landslide motion and applied to 26 cases of landslides and 6 cases of debris flows, with volume ranging from less than 100 m3 up to 3.5 × 109 m3. This quasi-three-dimensional model used the Navier–Stokes equation as the governing equation of motion and Coulomb’s resistance rule along the sliding surface to compute runout distance and coverage area corresponding with the real rheological conditions in the field. Due to the influence of dynamic conditions and excess pore water pressure, the internal friction of the sliding mass and the sliding surface are much smaller than the internal friction obtained by static soil tests. The moving volume affects the dynamic coefficient of friction and the velocity, whereas a small volume landslide occurs at a higher value of dynamic coefficient of friction and yields lower velocity. In addition, a landslide with a gentler slope occurs at a lower value of dynamic coefficient of friction, where in the case of the debris flow, it tends to have an even lower dynamic friction compared to landslide. This numerical model can be used to simulate the motion of rapid landslides with potentially long run-out in order to support hazard and risk assessment of landslides.