Study On Flow Mechanism For Avalanche Soils And Scour And Silting Characteristics Of Debris Flows

The author successfully simulated the rapid sliding of avalanche soils on mild slope with saturated soils in flume experiments, and the longest distance that avalanche masses can move was studied. It shows that the collapsing of loose avalanche soil is due to mixing of avalanche soils and water flow, and the collapsing of block avalanche soils is caused by resistance decrease due to overload pore water pressure. And then the author established and verified an empirical equation for the ratio of the heights of collapsed part and running part for the avalanche soils,suggested the critical flow conditions of loose avalanche soils and block avalanche soils, discussed the causes of accelerated motion of consistent debris flows on mild slope, and studied the average velocity of intermittent debris flows. Finally, the author also analysed the effects of convergence of debris flows on main channel, discussed the discriminant index of hazard of debris flows rushing into the main channel.The forecast of moving distance of avalanche soils-The ratio of the heights of collapsed part and run-out of avalanche soils is related to slope shapes, avalanche sources, streamwise soil conditions, runoff on foreside, and soil moisture. An empirical equation for the ratio of heights for the collapsed part and running part of avalanche soils was established and verified.The flow mechanism of avalanche soils-Collapsing of loose avalanche soils depends on soils moisture, longitudinal gradient, and mixing flows of avalanche soils and water flow. In which, the formation of different debris flows was discussed. Flow of block avalanche soils is caused by the resistance reduction due to pore water pressure. The supernormal pore water pressure between the block avalanche soils and underlay reduces the weight of block avalanche soils as well as the resistance between the block avalanche soils and underlay. And then the author also suggested the critical flow conditions of avalanche soils.cour and silting characteristics of debris flows-Because of resistance decrease due to supernormal pore water pressure, intermittent debris flows can be accelerated on mild slope in the superimposable processes of several debris flows. It shows that the accelerated effects can be caused by the superimposition of head of debris flows. And then different average velocity formulas of debris flows were studied, they all accord with the Manning's formula. These corrected formulas are very accurate.The effects of debris flows rushing into the main channel-The effects of debris flows rushing into the main channel are related to the angle between the gully and the main channel, the process of growth of debris flows, and the interaction of branch and main flow. The effectiveness can be expressed by the degrees of influence, danger and disaster of debris flows.