Outline and mechanical interpretation of slope failures in northern part of Hyogo prefecture caused by Typhoon No.9 in 2009

摘要

In August 2009, typhoon No.9 brought about a series of heavy rainfall over a wide area in Japan from Kyushu to Tohoku. In Sayo town in particular, the rainfall was most severe with the record of 89mm per hour. In northern part of Hyogo including Sayo town, sediment-related disasters such as landslides, debris flows, flooding etc. took place in many places. A majority of slope failures on the mountain flank occurred at places where the past wind-fallen trees were seen. In this paper, geomorphological features regarding the collapsed area on the mountain flank. Moreover, case study involved with in-situ and laboratory tests coupled with the stability analysis was carried out into the interpretation how the collapse took place. It was found that a total of 70 per cent of all the slopes damaged in the past with wind-fallen trees collapsed in the event of typhoon No.9. In addition, the shallow slope failure was caused by the loss of apparent cohesion when the surface soil was saturated.