STUDY ON THE THRESHOLD MOTION MECHANISM OF ENGINEERING SLAG DEBRIS FLOW WITH DIFFERENT PARTICLE SIZE GRADING CONDITIONS

Clear water flow is one of the main conditions for debris flow to start. Different water flows can cause debris flow on different scales. Using the indoor flume model experiment, the pore water pressure was measured with piezometer tube at three cross-sections. High resolution camera technology was used to record the movement of engineering slag and the collapse of skeleton particles. The results are used to analyze the phenomenon of slag in the process of debris flow formation. Based on the analysis, the experiment was conducted with fixing the slope angle of flume device of 8 degree. The clear water flow discharge was of 0.083 and 0.409 L·s^-1 respectively. The test results were used to analyze the effect of the flow state on soil particles failure and debris flow initiation under different clear water flow discharges. Under the action of the same clear water flow, the failure mode of the accumulated slag was mainly affected by the content of gravel particles. And the particle size of 2 mm in the slag had a greater influence on the content of gravel. When the particle size was larger than 2 mm and the content of gravel was greater than 50%, the failure mode of slag was mainly the undercut caused by erosion. The pore water pressure appeared increasing at beginning, and then stable. When the particle size was less than 2 mm and the content of gravel was greater than 65%, the failure mode of slag was mainly the bottom erosion caused by seepage. The pore water pressure was characterized by an arc-shaped rising with time.