Use of groundwater flow model in the analysis of a creeping landslide in western Japan

To predict the movement of an existing creeping landslide, monitoring and analysis of hydrological parameters are crucial. This paper analyses the hydrological parameters of an existing creeping landslide site in western Japan. The groundwater flow and resulting fluctuation in pore water pressure at the slip layer of a sliding block was simulated using a groundwater flow model. A quasi-three-dimensional factor of safety of the block was obtained by combining the groundwater model with slope stability analysis methods. The results show that for prediction purposes at a creeping landslide site the time series analysis using long-term data is of limited use, because the fluctuations of ground surface movement and hydrological parameters are not completely synchronized when the factor of safety of the slope soil is in the creep movement range. The ground surface movement rate dropped after each episode of relatively big movement, even when the hydrological parameters were constant. The factor of safety of the sliding block was more influenced by groundwater recharge from the hills than by rainfall. Pore water pressure fluctuation obtained from groundwater flow model resulting from specific rainfall events indicated better relations between fluctuations in pore water pressure 3 and ground surface movement.