Numerical simulation of the 1995 rainfall-induced Fei Tsui Road landslide in Hong Kong: new insights from hydro-mechanically coupled material point method

A rainfall-induced landslide case history in Hong Kong, i.e., the Fei Tsui Road landslide on 13 August 1995, is simulated in this study using a two-phase material point method (MPM). With the aid of hydro-mechanically coupled two-phase MPM, the entire process of the landslide case history is simulated, starting from rainfall infiltration, to advancement of wetting front, evolution of pore water pressure spatial distribution, triggering of multiple failure events, and post-failure large deformation of soils. The simulated results agree well with the field observation during the incident in 1995. Two separate failure events (i.e., one major failure occurred about 20 min after a minor failure) observed during the landslide are properly simulated by the two-phase MPM. The simulation also shows an accumulation of perched water that is consistent with a water table of less than 4 m observed during the incident. In addition, new insights into the failure mechanism are obtained from the simulation. The major failure event observed during the landslide is found to contain two different failure modes, one shallow failure and one deep failure. In the previous study, a weak layer of kaolinite-rich altered tuff was believed as a principal reason for the unusually large volume of sliding soil mass. However, the MPM parametric study in the manuscript shows that the weak layer only has a minor effect on the incident.