抄録
Soil pipes are known to have significant impacts on the effective hydraulic conductivity and the storm runoff generation in slopes. Thus, pipeflow must strongly contribute to sediment movement on slopes and subsequent shallow landslide initiation. However, the effects of pipeflow on shallow landslide initiation have not been understood sufficiently because of the limited information about the mechanism of runoff and erosion by pipeflow. Hydrological observations and investigations of soil pipe morphology were conducted in the Toinotani, Kyoto University Forest in Ashiu. Based on the results of field measurements, the pipeflow agent, which affected the changes in safety factor on slopes, was evaluated by numerical calculation combined with the well-drainage theory. The calculation showed that once a collapse of the pipe walls causes clogging of a soil pipe, the value of the safety factors of the slopes with lower hydraulic conductivity soils promptly decreased with reaching below 1.0 within 200 seconds after the clogging of the soil pipe. Here we show that the clogging of a pipe outlet can play an important role in landslides initiation, which occurred at the time of the highest rainfall intensity.
