Investigating the Groundwater Variation and Deformation Kinematics of Large-scale Landslide Under Different Rainfall Patterns Using 3D FEM Analysis

The deformation of large-scale landslides poses a long-term threat to the protected objects in mountainous areas. Recent hazard records show that torrential are critical in triggering the deformation of large-scale landslides. This study investigates the relationship between groundwater variation and deformation kinematics of a large-scale landslide under different rainfall patterns using 3D FEM analysis. The case study of the  Guanghua slope, located in Taoyuan, Taiwan, has been identified as an active large-scale landslide since 2018. A geomechanical model was established based on borehole and outcrop investigations. To correlate the rainfall pattern and groundwater change, the groundwater well data and the rainfall record from 2021 Typhoon In-Fa were used to assess representative groundwater unit hydrographs for the Guanghua slope. Then, different groundwater table scenarios associated with given rainfall return periods can be constructed as the hydraulic boundary condition. The surficial displacement data from GNSS observation and digital image analysis was used to calibrate the performance of 3D FEM models. The results show that the 3D FEM analysis well captured the deformation kinematics of the Guanghua slope, including movement direction and deformation displacement. The current study demonstrates a practical methodology to clarify the changes in the groundwater table and slope movement under different rainfall patterns for assessing the potential disaster scenarios of a large-scale landslide.