Alternative Title土石流被害軽減のための実践的な土石流速推定手法の探求
Note (General)Debris flow is one of the shattering natural disasters, mostly ensuing in mountainous areas. Rational estimation of debris flow velocity is one of the key issues in debris hazard mitigation. Among the various procedures, back-calculation of debris flow velocity is a widely used approach. Back-calculation procedure includes determinations of super-elevation and channel properties, and velocities are calculated using the forced-vortex equation (??=√gRΔ?/kb). A debris mass, when travels through a curved flume, leaves the highest flow mark on the outer bend, and the difference between the flow depths of outer and inner bends is referred to as ‘super-elevation’. However, in a post-flow field investigation, only the highest flow marks on both inner and outer bends are visible, which does not portray the actual maximum super-elevation that must have been reached in the unsteady flow event, and eventually leads to a misjudgment of the real velocity. Another important parameter of forced vortex equation is the channel radius of curvature. Any natural channel has hardly been a circle, rather it has varying curvature. How the curve is approximated can affect velocity estimation. Considering the unsteady nature of debris flows, this research work aims to figure out a coherent way of estimating debris flow velocities. Therefore, a series of numerical curved flume tests using Smoothed Particle Hydrodynamics (SPH) are carried out to check the aptness of the mud-marks derived velocities. Estimated velocities from flow marks underestimate the actual velocities near the source, while they converge on the actual velocities as the distance to source increases. Based on the simulations, a best fit curve is proposed to adjust the mud-marks derived velocities. Law of similarity allows to apply the findings from these small scale simulations to the real debris flow problems. Three debris flow events in Japan are taken for the validation of the proposed procedure and adjusted velocities are proven to be consistent with verbal evidences and previous analyses.
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2017-04-02T16:10:31+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション