Experiment Of Initiation Mechanism Of Landslide Translation To Debris Flow

Debris flow and landlisdes are main hazards in mountainous area. In China, they are usually induced by rainstorm, occupying more than 90% in number and 95% in economic loss caused by by such hazards. The research on initiation of debris flow is the focus of both theoretical and practical significance. And in particular, the study on translation of landslide to debris flow is of great importance, which as a new project has been put forward in recent years. And it is the center point in the thesis.This research lies on the intersect part of debris flow initiation and landslide dynamics. It is worth to put it in practice in theory.We select Jiangjia Ravine to be the study basin and select wide-graded gravel soil as test material. The initiation mechanism on a soil-type debris flow has been researched based on field prototype observation, man-made rainfall experiment, and the dynamic triaxial test. Main conclusions can be drawn a sfollows:1) Three kinds of initiation can be identified: debris flow initiates on slope from shallow layer of soil at the stimulus of heavy rainfall;debris flow from failure of thick layer of soil at moderate and durable rainfall;debris flow formed by the entrance of great block of soil into channel at moderate and light rainfall. And two mechanisms have been proposed: vibration softening or liquefaction under heavy rainfall, and local softening and liquefaction under moderate and light rainfall. Difference between them relies in the manner of pressure of pore water.2) Different filtration exists in soils of wide-ranged particle composition, which causes redistribution of grains of moderate and small sizes along the route of filtration: concentration of coarse grains in the entrance and that of fine grains in the outlet. This suggests that such process should be a new way of inner erosion.3) Before the initiation of debris flow, pore water pressure jumps and water potential waves rapidly in some certain frequencies;accordingly, soil temperature waves, indicating exchange of energy.4) Short-term test of soil consolidation indicates that the regular fluctuation of water potential before failure is the intrinsic feature of soil with wide-ranged grains, relating to the catastrophic mechanism of soil failure. Furthermore, dynamical triaxial test also presents strength fluctuation of soil, indicating it is a phenomenon occurring at a certain range of water content and vibration load beyond which it disappears.5) Debris flow induced by rainfall follows the route of formation: rainfall process -? change of soil water moisture, change of soil structure and composition -> change of soil strength -? change of slope stability -> soil break (start of landslide) — formation of debris flow on slope -? formation of debris flow in gully. If relationships between the successive steps are established, we can forecast the occurrence probability, occurrence time and the magnitude of debris flow by using rainfall data.These results are to be helpful for the future studies on constitution equation of soil, on dynamical calculation of soil failure, on confluence of debris flow, and ultimately on the forecast of debris flow.