1999 Fiscal Year Final Research Report Summary
Unified View of the Mechanics of Debris Flows and Sediment Laden Flows
| Project/Area Number |
09450190
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | Ritsumeikan University |
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Principal Investigator |
EGASHIRA Shinji Ritsumeikan Univ., Fac. Science and Engineering, Professor, 理工学部, 教授 (00027286)
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| Co-Investigator(Kenkyū-buntansha) |
MIYAMOTO Kuniaki Tottori Univ., Center for Joint Research and Development, Ass. Professor, 地域共同研究センター, 助教授 (00263492)
NAKAGAWA Hiroji Ritsumeikan Univ., Fac. Science and Engineering, Professor, 理工学部, 教授 (60027216)
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| Project Period (FY) |
1997 – 1999
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| Keywords | debris flow / sediment gravity flow / med flow / flow with bed-load / flow with suspended load / sediment transport rate formula / constitutive equations |
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| Research Abstract |
This study has attempted a unified treatment of the following themes : the constitutive relationships of flowing water-sediment mixture, the profiles of sediment concentration and flow velocity from debris flows to flows with both bed-load, and "clear" water lagers to calculate the reference concentration of suspended flows. In this study, the constitutive relationships proposed by Egashira et al. include some physical parameters : the sediment size, the interparticle friction angle and specific weight of sediment etc.
The effects of interparticle friction angle on debris flows have been investigated experimentally and theoretically for two years. The following results were obtained : in debris flows over rigid beds, an increase of interparticle friction angle causes flow resistance to increase. On the other hand, in debris flows over erodible beds, the inverse tendency appears.
The influence of sediment size on flow of sediment-water mixture were investigated experimentally and theoretically. An experiment was employed with different sizes of sand, in the region from debris flows to the flows including a clear-water larger. The data obtained by flume tests were compared with the numerical simulated profiles of velocity, and sediment concentration. The calculated results agreed well with the flume data. The sediment transport rate became small when the sediment size was large, and became large when the sediment size was small for both large or small bed shear stress.
Methods to predict the reference concentration and reference level of suspended flows were proposed using Egashira et al.'s constitutive relationships and taking the vertical distribution of the Reynolds' stress into account According to this method, the reference concentration was small when the sediment size was small. The calculated results were fitted with previous experimental data obtained by many researchers.
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