Study On The Formation Mechanism Of Debris Flow Under Slope Runoff

Debris flow is a unique natural disaster in mountainous regions. It is widelydistributed, according to statistics, more than190countries and regions around theworld, more than60countries and regions have suffered debris flow, or evencatastrophic destruction. Taking loose soil on slope as the research object, consideringthe effect of slope runoff, and using hydrology, fluid mechanics, soil water dynamics,material mechanics and limit equilibrium theory, the formation mechanism of debrisflow under slope runoff has been revealed from three aspects: the formation andevolution of infiltration front, the effects of infiltration of slope runoff on physical andmechanical properties of soil, and mechanical mechanism for the formation of debrisflow under slope runoff. The results are shown below:(1) Based on Green-Ampt infiltration model, and combining the Philip infiltrationmodel, the calculating method for the depth of infiltration front under slope runoff hasbeen established, and its rationality has also been proved by an infiltration experiment.(2) Taking the soil from infiltration experiment for example, the evolutioncharacteristics of infiltration front have been obtained. The results reveal that the depthof infiltration front is increased with the increase of cumulative infiltration, and they arein linear relationship; with the downward of infiltration front continuously, theinfiltration rate is reduced, and both of them as a decreasing function; and theinfiltration front and t are in linear relationship.(3) Based on the direct shear experiment, the results show that for the samples withdifferent kinds of water content and dry density, the angle of internal friction isdecreased with the increase of water content, while the cohesion is in parabolicdistribution with the increase of water content. Through numerical calculation, theeffects of infiltration of slope runoff on the slope saturation line, pore water pressureand volumetric water content rate have been analyzed. Thereby, the effects ofinfiltration of slope runoff on physical and mechanical properties of soil have beenrevealed.(4) The normal stress and shear stress on inclined plane have been solved bymaterial mechanicals, and the cracking mechanism of soil under slope runoff has alsobeen explained. Considering runoff shear force, hydrostatic pressure of water in crackand runoff impact force and using limit equilibrium theory, the stability calculation method under slope runoff has been estabilished, and based on an example, the resultshave revealed that under natural conditions, the slope is in a stable sate, while, underslope runoff, the stability factor is less than1, and decreases by75%.