Prediction of Viscous Debris Flow and Its Mitigation

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The research aimed to make clear the mechanism of flow, the process of occurrence and the method to cope with for the viscous type debris flows. The joint research has been implemented by observing the actial flow in the Jiangjia test field in Yunnan Province, china together with the basic research in the laboratory.Every time when the Japanse staff members visited the test field, the debris flow occurred and the details of the actuality of the flow were grasped. Different from the stony type debris flow, the viscous type debris flows have happened rather long after the intense rainfall and they have appeared as the numerous surges. From these characteristics a conclusion that each surge has been produced by a small scale landslide has deduced.The viscous debris flow used to be explained by the Bingham fluid model that attributed the stoppage of the flow between the successive surges to the yield strength of the material. The data of the observation, however, denied the existence of such a strength, and therefore a new Newtonian fluid model was introduced. The mechanism for supporting concentrated solid particles in the laminar Newtonian fluid was made clear and formulae for deposition velocity of the particles and for the resistance to flow were deduced. Thereby, a numerical simulation of the debris flow became possible.The deatailed survey of the topographical change before and after the debris flow and the examination of the effectiveness of the countermeasures in the actual basins suggested the principle to cope with the viscous debris flows.