Research on Formation Mechanism of the Debris Flow on Slope Induced by Rainfall

Abstract

Based on field investigation and lab tests, rock and soil fracture criterion, and analyses of typical debris flows on slope, the formation mechanism of the rainfall-induced debris flow on slope have been studied by considering its influential factors, kinematics properties, dynamic conditions, and formation and evolution process of the debris flow on slope. The research results indicate that the debris flow on slope is mainly of the type of translational slide failure, which is developed on the steep slope, where gradient is more than 40° with shallow residual soil (thickness is less than 2.0 m). The rainfall is one of the important factors inducing the debris flow on slope. Rainwater penetration makes the residual soil saturate and soften. When water content of the residual soil is more than 28%–30%, the relation curves of cohesion and internal friction angle versus water content show obvious inflexion. That is, when the saturation of the residual soil is more than 75%, the cohesion and internal friction angle both decrease rapidly. The soil on slope will change from stable to destructive. The residual soil will start to form partly mollisol and slip down the slope if it meets persistent rainfall or rainstorm. Further, the sliding soil mass rushes down to create mud slurry-debris flow on slope.