Formation and developing processes of debris flow resulting from slope failures

Shinji EGASHIRA, Kuniaki MIYAMOTO and Hiroshi TAKEBAYASHI

Present study describes formation and developing processes of debris flow resulting from landslides and slope failures, supposing that a soil block released by slope failure is saturated by water. Stability and mobility analyses of the soil block such as an equilibrium bed slope suggest that the soil block is fluidized resulting into debris flow, and that the resulted debris flow is able to reach a milder area than expected for the debris flow composed only of coarse sediment, supposing that a phase sifting takes place from solid phase to liquid one for the fine material composed of the soil block. In addition, the results show that the debris flow size such as a peak flow discharge is determined mainly by sediment erosion along the torrent bed except in the sediment depositional region. Such results provide a key for designing sediment control facilities, which is very different from a conventional method.