Characteristics of rain infiltration in soil layers on the hillslope behind important cultural asset

Abstract

Recently, slope failures have occurred due an increase of heavy rainfall and typhoon events. As typical examples, sediment disasters have occurred frequently at Kiyomizu-dera Temple, including debris flows in 1972 and shallow slope failures in 1999 and 2013. Kiyomizu-dera temple is a UNESCO World Heritage Site, and one of the Historic Monuments of Ancient Kyoto, Japan. An increase in shear stress and decrease in shear strength due to infiltration of rainwater led to slope failures. In this study, subsurface water movements were investigated by measuring pore water pressure changes and hydraulic gradients during rainfall events to prevent damage to important cultural assets by natural disasters. Saturation was found to occur after very small rainfall events, regardless of soil moisture conditions. Although subsurface water normally flows from upper to lower areas of the slope, water movements from the bedrock to the soil layer were observed during rainfall events, suggesting the existence of potentially hazardous slope failure conditions.