The simulation of a deep large-scale landslide near aratozawa dam using a 3.0 Mpa undrained dynamic loading ring shear apparatus

Abstract

The translational block glide of deep and large-scale landslide near the Aratozawa dam that occurred in the middle of 2008 is of great importance for detailed study. Aratozawa landslide had resulted from landform deformation and the subsequent change of watershed geomorphology at the upstream part of the Aratozawa reservoir. The evidence of this phenomena was revealed during a site investigation in November 2012, as several natural reservoirs (lakes) formed in the cavities between ridges and the depression zone in main block slide. Aratozawa landslide located in the Ohu Mountains basically was triggered by the earthquake which had a peak ground acceleration of more than 1,000 gal. In addition, the possibility of reactivated landslides in surrounding terrains near Aratozawa dam has resulted in the hypothesis that the 2008 event was one sequence of the dynamicgeomorphological activity in this mountainous area within a period of hundred years. In this paper, the mechanism of the deep and large-scale landslide near Aratozawa dam is analysed through a physical laboratory experiment. Deep landslide simulation is conducted by applying high normal stress to address the assumed slip surface of 150 m depth in the Aratozawa case. The 3.0 MPa undrained dynamic loading ring shear apparatus with the high pore-water pressure controlled is used to meet the criteria of deep-seated landslide of Aratozawa. The effect of groundwater fluctuation and the inter-linkage with the reservoir in the Aratozawa dam was found to be the main concern besides the peak ground acceleration based on the 2008 landslide event. Results also show that there was no significant deformation in the Aratozawa dam area when the large Tohoku earthquake, magnitude 9.0, in 2011. Indication is, that the slide blocks, ridges and mass depression due to the 2008 event are already stable. However, the slope and soil mass movement are still possible in the future.