Yumokjeong Landslide: an investigation of progressive failure of a hillslope using the finite element method

The presented case study describes the progressive movement of a shallow landslide in Central South Korea after excavation of its toe and subsequent, sustained above-average rainfall. Measured soil data as well as real-time measurements of slope movement and precipitation enabled calibration of a numerical model based on the finite element method (FEM) to capture the destabilization and associated movement of the slope. The numerical model employed the Bishop's effective stress approach to define the state of stresses in unsaturated soils, as well as transient seepage analyses to introduce the non-uniform effects of actual rainfall data into the analysis. The resulting model provided insight into the complex behavior of a progressively failing slope. It demonstrates that use of numerical methods like FEM that allow for coupled transient unsaturated seepage-stress analyses presents a means of evaluating the progressive failure of slopes under rainfall. Furthermore, it demonstrated that for certain slopes under partially saturated conditions, sustained above-average rainfall may cause shallow landsliding when driven by stimuli like excavation. Additionally, the kinematics of failing slopes may not always follow classical slope stability approaches (sliding block method, circular method of slices, log-spiral, etc.) prior and during slope failure. The given kinematics of a slope failure may change with movement, redistribution of principal stresses, and dissipation of suction stress. Therefore, analyses like FEM present a unique tool to evaluate the deformation behavior of failing slopes on a case-by-case basis.