Study On The Mechanism Of Starting And Handling Rules Of Boulders And The Impact Force In Debris Flow

5.12" Wenchuan earthquake triggered a large number of debris flow, collapses, landslides secondary geological disasters, which resulting in large area of slope rock and soil loosening, and it will changes for a lot of loose accumulation material under the condition of short rainfall, that can be seen everywhere more than 1m diameter giant gravel in loose packing material. The loose deposits provide the source for the outbreak of debris flow, and the boulders in the debris flow exacerbated hazards for housing?pier and the dam. Therefore, it`s necessary to study on boulders in debris flow startup and handing rules and after the start of the impact force. Which is not only the evaluation of debris flow risk assessment and is an important index for building anti debris flow strength, it also provides important parameters for the design of debris flow control engineering at the same time.The paper is based on the field investigation, which focused on boulders in debris flow by indoor experiment method, so that it will have a thorough understanding on the startup and handing mechanism of boulders. Through a large number of large-scale indoor flume experiment, and considering the influence of different shapes and different quality of boulders?and different debris flow volume concentration of solid, which find some laws of the results. Draw the following conclusions:(a) Under the same conditions, different shapes of the Boulder has a different start and transporting mode, of course the boulders which has different quality also has a different start and mode of transport.(b) In different conditions, the flow velocity of debris flow decreased with increasing the volume concentration of solid phase. But a boulder start in a way that is consistent with the same one in different conditions, and a mode of transport is also similar, it only differs in the migration of the acceleration and the average velocity, and the average speed of boulder transport decreases with the slurry volume concentration of solid phase increases.(c) The pulse signal of debris flow is a relatively smooth curve, it is due to a long time for the impact of boulders, which the signal often concentrated in a low frequency band in the frequency domain. However the impact of boulders in debris flow is discrete pulse signal, because it takes a very short time for impacting of boulders, which the signal often concentrated in high frequency in the frequency domain.(d) The impact value of the boulders relates to quality of the boulders and migration velocity of the boulders. Under the same conditions, when the migration velocity of the boulders is beyond a certain value, the impact force of the boulder is determined by the transport speed, but when the migration velocity is small, the impact force increases with the quality of boulder increase. With the increase of debris flow slurry volume concentration of solid phase, the impact force is significantly reduced. A boulder which is the same site inside a tank of water can be obtained the impact force increases with transport velocity increase under two conditions.