Detail Study of the Aratozawa Large-Scale Landslide in Miyagi Prefecture, Japan

The deep large-scale landslide near Aratozawa Dam in Miyagi Prefecture of Japan was occurred in 2008 and still the initiation mechanism and motion behavior were not explained in detail up to now. This paper aims to report briefly the detail study of the Aratozawa landslide. We conducted several experiments to test the Aratozawa samples using the newest version of the undrained dynamic loading ring shear apparatus. As reported by Sassa et al. (2014), the ring shear apparatus was designed with the single central axis-based for the normal stress loading system, with the normal stress and pore pressure measurement capacities of up to 3.0 MPa. The friction coefficient, shear displacement at the start and end of shear strength reduction, mobilized friction angle and steady state shear resistance of the Aratozawa samples were obtained from the ring shear tests. Experiments results implied that the shear strength reduction in progress of shear displacement of the Aratozawa samples was caused not only by the earthquake but also by factor of the initial pore pressure (Setiawan et al. 2014, 2016). Further analysis has been conducted by occupying shear parameters of soil failure resulted from experiment as a critical inputs for the LS-RAPID geotechnical simulation. LS-RAPID landslide simulation model is used to observe the overall process of landslide phenomena started from initiation to moving process. The Aratozawa landslide was successfully simulated using LS-RAPID model which involves the pore pressure increase, seismic loading, and landslide volume enlargement during traveling process. However, factor of the reservoir and its relation to the groundwater and bedrock is still needed to analyze in further.