Infiltration of Rainwater from Slopes of Pyroclastic Flow Deposits Using Automated Electrical Prospecting

摘要

Rainfall and its infiltration from the slope surface may be one of the most important factors for slope failures in monsoon regions such as South and East Asia. To obtain the process of the infiltration of rainwater, temporal changes of the apparent resistivity inside of the slope have been measured using automated electrical prospecting in southern Kyushu, Japan. A target slope is underlain by the Quaternary pyroclastic flow deposits characterized by soft and permeable properties. Results of measurements after a heavy rainfall indicate decrease in apparent resistivity value and its inward extension. This suggests that the inward infiltration of rainwater have proceeded from not only top surface but also slope surface. The decreasing of the resistivity continues for longer than a day in deeper portion, and consequently, the effect of the infiltration was recognized extending over 20 meters from the surface. On the other hand, the resistivity value tends to change rapidly between wet and dry in response to weather condition in shallower portions, while it changes very slowly in deeper portion.