Study On Slope Erosion And Material Movement Characteristics Of Jiuzhaigou Under Post-earthquake Rainfall

Jiuzhaigou area was affected by the "8.8" earthquake,which resulted in a large number of loose granular deposits.Under the action of rainfall,two debris flows broke out in Jiuzhai Tiantang debris flow gully,Jiuzhaigou County,on June 26,2018 and July 10,2018.The debris flow accumulation blocked the gully and raised the water level of the main gully by 1 m,resulting in the erosion and collapse of the opposite bank slope.In this paper,Jiuzhai Tiantang debris flow gully in Jiuzhaigou County is selected as the research object.The development of Jiuzhai heaven debris flow gully is studied through field investigation and multi-phase high-resolution drone images.Using indoor image processing and particle division test methods,the migration characteristics of the particles of the loose landslide accumulation after the earthquake under the action of rainfall were studied.On this basis,a physical model test was used to simulate the process of surface runoff formation on the slope surface under rainfall conditions,and the process and characteristics of slope mudslide start-up,material movement and erosion were studied.The physical simulation test mainly considers the influence of the three main factors of slope,initial moisture content and fine particle content.The main research contents and results are as follows:(1)According to field investigations revealed that earthquake-induced loose accumulations of landslides accumulated on the slope,and the erosive debris flow on the slope was produced by rainfall after the earthquake.Through field sampling and particle size test,the particle gradation of the loose accumulation on the slope of the source area was obtained,and the test gradation was obtained after translation.The rainfall is controlled by the rainfall system to 4mm / min,and the water pipe is adjusted to 4.5kg / min to simulate the law and control factors of runoff erosion on the surface of a large number of loose accumulations under the effect of rainfall.(2)The slope erosion test by changing the slope found that within a certain range,the increase in slope will increase the erosion of the slope body.For a steep slope,due to the loose accumulation on the slope surface is close to its natural angle of repose,As a result,the slope flow can also be started under the unsaturated state of the accumulation body.During the saturation process,the slope failure will promote the formation of slope flow.When the slope increases,the gullies develop from the top of the slope body,and the sides of the gullies are more likely to be unstable and widen,and the undercutting effect is stronger.(3)The slope erosion test by changing the initial water content found that within a certain range,the increase of the initial water content will change the way of rainfall and surface diameter flowing into the slope body,and will accelerate the overall saturation speed of the slope body.Lifting,slope erosion increases,and when the initial water content increases,gullies are easier to form,and gully erosion is deeper.However,in the 2% initial moisture content test in this test,due to the instability of the front of the slope body,the erosion amount is much larger than that of the other two groups.According to the analysis of the test data,the slope body begins to saturate under the action of rainfall and runoff,and the slope body is fine.The particulate matter moves under the package of the water film,blocking the pores between the particles in the slope body,causing water to accumulate inside the slope body,so that the pore water pressure in the slope body surges to form an excessive pore water pressure,which causes the slope to be unstable and damaged.(4)The slope erosion test by changing the content of fine particles found that the content of fine particles in the soil directly affects the porosity of the soil,and then affects the water holding capacity of the soil.As the content of fine particles decreases,the slope surface is difficult to form with effective runoff erosion,the amount of erosion is also reduced.At the same time,the fine particles have a lubricating effect on the movement of materials in the erosion of the slope,and the larger particles can be transported under the same conditions.