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Application of an MPS-based model to the process of debris-flow deposition on alluvial fans
Suzuki, Takuro Hotta, Norifumi Tsunetaka, Haruka Sakai, Yuichi
Suzuki, Takuro
Hotta, Norifumi
Tsunetaka, Haruka
Sakai, Yuichi
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2019
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Abstract
A modified moving particles simulation model (MPS-DF) to simulate inundation and sediment deposition of debris flows is presented. This model is based on the moving particles semi-implicit (MPS) method, which was originally used for incompressible viscous fluid flows with free surfaces. In the MPS-DF model, the constitutive equations of Egashira is introduced to the MPS method. In Egashira’s theory, debris flows are treated as a continuum and sand grains are expressed using sediment concentration. Thus, each particle has a variable sediment concentration value. In this study, we tested the applicability of the MPS-DF model for the formation process of alluvial fans. For this purpose, flume experiment was conducted. The experimental flume consisted of a straight channel 6.0m long and 0.1m wide, with an inclination of 15°, connected to an outflow plain. The inclination of the outflow plain decreased gradually from 12° to 3°. At the straight channel, 5.0m long erodible bed with a thickness of 0.2m was present. Water was supplied from upper end for 60 s. at the rate of 3,000 cm3/s and debris flow was generated by entraining the erodible bed. Debris flow inundated and deposited sediment at the outflow plain and an alluvial fan was formed. Numerical simulations were also performed with the MPS-DF as well as a depth-integrated method based on the shallow water equations (2D simulation). 2D Simulation results of alluvial fan shape and flooding area were laterally spread and significantly different from those of experiment. The results of the MPS-DF were more similar to experimental results. Natural channels and lateral levees were formed as well as experiment. However, the alluvial fan shape of MPS-DF was slightly wider than that created during the experiment. This is thought to be due to the behavior of pore water of deposied layer, such as the seepage of water out of the deposited layer once the deposition process has been completed.
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