HR: 0830h
AN: H31C-0488    [PDF]
TI: The effect of pore water pressure on debris flow dynamics
AU: * Okura, Y
EM: ohkur03@ffpri.affrc.go.jp
AF: Forestry and Forest Products Research Institute, P.O.Box16, Tsukuba-Norin, Ibaraki, 305-8687 Japan
AU: Parker, G
EM: parke002@umn.edu
AF: St.Anthony Falls Laboratory, University of Minnesota, 2 Third Ave. S.E., Minneapolis, MN 55414 United States
AU: Marr, J G
EM: marrx003@umn.edu
AF: St.Anthony Falls Laboratory, University of Minnesota, 2 Third Ave. S.E., Minneapolis, MN 55414 United States
AU: YU, B
EM: yuxxx081@umn.edu
AF: St.Anthony Falls Laboratory, University of Minnesota, 2 Third Ave. S.E., Minneapolis, MN 55414 United States
AU: Ochiai, H
EM: ochi@ffpri.affrc.go.jp
AF: Forestry and Forest Products Research Institute, P.O.Box16, Tsukuba-Norin, Ibaraki, 305-8687 Japan
AB: Pore-water likely plays an important role to reduce shear force in debris flow. In experiments, we observed pore-water pressure during flow to clarify the relationship between the flow speed and pore water pressure which would be affected by flow depth and particle size distribution. Soil materials were prepared with mixing materials of sand, silt and clay. Pore-water pressure on the flume bed, flow depth, velocity and run out distance was observed, and the following results were quantitatively obtained in this series of experiments. 1. A positive relation was observed between strain rate and pore-water pressure ratio in the flow. The strain rate and pressure ratio were dimensionless parameters of the ratios of surface velocity to flow depth and pore-water pressure head to flow depth, respectively. This relationship indicated that shear resistance decreased as the pressure potential leading to acceleration of flow velocity increased. 2. A positive relation was also observed between flow depth and pore-water pressure ratio. This indicated that the pore pressure diffusion became increasingly obstructed as the flow depth increased. 3. The pore-water pressure ratio tended to increase with the uniformity coefficient of debris flow materials. The reason for this might have been that smaller particles suspended in the flow increased pore-water pressure, and the wider range of particle distribution effectively prevented pore-water pressure diffusion. 4. There was an apparently negative correlation between the equivalent coefficient of frictions and the pressure ratios. Equivalent friction is apparent friction during flow. The most likely reason for this is that shear resistance would decrease and run out distance increase as the pressure ratio increased. These results indicated that the effect of pore water fluctuations should be one of the most important factors affecting the shear resistance in debris flows. This work was supported by the National Science Foundation under Agreement Number Ear-0120914, and was partly supported by an overseas research fellowship from the Japan Society for the Promotion of Science (JSPS).
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting