Abstract. In order to investigate the complex nature of landslides triggered by rainfall, dynamic muon radiography of the motion of the underground water table is planned in a drainage tunnel drilled underneath an estimated fault plane. However, the humidity inside the tunnel is almost 100 %. In order to suppress moisture effects, a scintillation counter with Cockcroft-Walton photomultipler tubes (CW-MPT) was developed and tested at the observation site located in Shizuoka Prefecture, Japan. The counter was stably operated for 38 days without gain degrading. Based on the result, we constructed a muon detection system with CWPMTs at the same site and started operation runs. In this work, the data from borehole-based water gauge measurements of the underground water levels were analyzed and discussed. It was confirmed that the comparison between muon and borehole data would be useful.
In order to investigate the complex nature of the landslides triggered by rainfall, dynamic muon radiography of the motion of the underground water table is performed in a the drainage tunnel drilled underneath an the estimated fault plane. However, the humidity inside the tunnel is almost 100%. In order to suppress the moisture effect, a scintillation counter with Cockcroft-Wwalton photomultipler tubes (CW-MPT) was developed and tested at the observation site. The counter was stably operated for 38 days without gain degrading. Based on the result, we constructed a muon detection system with CW-PMTs at the same site and started operation runs. In this work, the data from borehole-based measurement of the underground water levels were analyzed and discussed. It was confirmed that the comparison between muon and borehole data would be useful
Recently, landslide due to natural disasters such as large-scale typhoons, or local torrential rain as a consequence of climate change, has become a serious problem for effective and detailed management of infrastructure safety. Particularly, slopes at risk of large-scale landslide in the future should be evaluated across the entire slopes for the behavior of groundwater infiltration from heavy rainfall. It is very important to establish monitoring techniques to visualize rainwater infiltration across entire slopes for the long term management of landslide risks. The authors developed a new electrical exploration system for remote-controlled measurement. We conducted a continuous electrical survey over a period of two years at two slope sites in order to monitor rainwater infiltration of landslide slopes. Based on resistivity changes during rainfall events of 50-100 mm, the findings indicate that rainwater rapidly infiltrated shallower sediments to depths of a few meters during rainfalls, and evaporated slowly after rainfall ceased. We also estimate that rainwater penetrated slowly into deeper layers. The sampling period was limited to 50-60 days, due to frequent methodological challenges such as the severing of cables by wild animals and rock falls, and instrument failure caused by the thunderbolts at two sites. Furthermore, we were unable to continue the measurement during heavy rainfall events of more than a few hundred millimeters. The biggest factor is that the instruments were not protected from thunderbolts during storms. It is recommended that future studies should incorporate protective circuits for thunderbolts to double or triple insulation.
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