[H-DS07] 地すべりおよび関連現象

[HDS07-11] Influence of grain-size distribution on formation of debris-flow fan

*經隆 悠¹、堀田 紀文²、酒井 佑一²、西口 幸希³、日名 純也³ (1.筑波大学生命環境科学研究科、2.東京大学大学院農学生命科学研究科、3.株式会社建設技術研究所)

キーワード：土石流、土石流扇状地、水路実験、PIV、SfM

Accurate prediction of debris-flow fan formation is critical to sediment disaster mitigation because most damage from debris flow occurs in the inundation area. Although actual debris flows include a diversity of grain sizes, assessment is generally based on numerical simulation results for monogranular debris flows. This study conducted flume tests of debris flows using 0.08 m³ of sediment particles that were either monogranular (2.65 mm) or a mixture of seven diameters (0.7 to 6 mm; average size of 2.65 mm) and compared formation processes of debris-flow fans to examine the influence of grain-size distribution. Channels (15°, 10 cm wide) with a deposition area (12° to 6°) were used for the experiments. We captured the development of the debris-flow fans using photographs and videos made by digital cameras and used the techniques of Structure from Motion (SfM) and Particle Image Velocimetry (PIV) to monitor debris-flow fan formation and flow regimes. As a result, monogranular debris flows produced an approximately symmetric debris-flow fan. In contrast, multigranular debris flows produced an asymmetric debris-flow fan, and the topography and range differed in each case. These results suggest that grain-size distributions of debris flows affect the process of debris-flow fan formation.