Numerical simulation of rainfall-induced deep-seated landslide in Lantai area, Taiwan

Due to the geographical characteristics, the intense rainfall brought by typhoons frequently triggers landslides and debris flows in Taiwan, posing significant risks to lives and properties. The deep-seated landslide in the Lantai area, northern Taiwan, is adopted in this study. Rainfall records from the Central Weather Bureau of three significant typhoon events from 2019 to 2022 were analyzed, and the total effective cumulative rainfall records were derived (Lee, 2006). The seepage analysis was then performed to obtain the groundwater level time variations caused by the rainfall. We conducted numerical simulation of the three events using a commercially available program Geostudio. The numerical analysis starts by simulating variation of groundwater level caused by rainfall, and the time variation of groundwater level was implemented in the slope stability analysis adopting limit equilibrium method. Results of seepage analysis indicate a strong correlation between the total effective cumulative rainfall and groundwater level variations. The time variation in the factor of safety reduction was deduced by accounting for groundwater response delays. The results were validated against on-site monitoring data, and the sliding surfaces were compared to the borehole logging and geological profile. The threshold groundwater levels for the Lantai area deep-seated landslide can then be estimated to range between 20.22m and 20.04m below ground surface, which can be used for issuing a landslide early warning.