A Study On Starting Mechanism And Shallow Prevention Measures Of Landslide Sandy Debris Flow Under Combined Actions Of Wind And Rainfall

China is a country with a vast territory,diverse climatic conditions and complex topography.While our country enjoys the advantages of natural resources,it also faces the threat and challenge of many meteorological and geological disasters.Among many natural disasters,debris flow is one of the most non-negligible disasters.Debris flow is characterized by strong destructive force,large scale,ambiguous spatial and temporal patterns,and difficult to prevent and warn,so it is important to study the starting mechanism and prevention measures of debris flow.The study of debris flow is highly interdisciplinary,with many predisposing factors and complex mechanisms of action.This paper selects wind and rainfall as the core research content among many triggering factors,and conducts laboratory test and numerical simulation research on the starting mechanism of debris flow.The main research work is as follows:Firstly,indoor sand and soil debris flow tests with variable wind speed and rain intensity were conducted to study the starting mechanism of debris flow under the combined effect of wind and rain.The analysis of test macroscopic phenomena,water content changes and other aspects are carried out to investigate the movement pattern of sand and soil debris flow under the combined effect of wind and rain.It was found that when rainfall acts alone on the surface exposed slopes,the time required for debris flow initiation gradually decreases as the intensity of rainfall gradually increases.When wind speed and rainfall act together on the slope and the wind speed is 6 m/s,the combination of wind and rainfall will contribute to debris flow starting.When the wind speed level exceeds6 m/s,the change in wind speed will have a delaying effect on debris flow starting.When the rainfall intensity increased from 400 ml/min to 1000 ml/min,the strong rainfall weakened the differential effect of different wind speeds on starting time of debris flow,so that the starting time of debris flow for each test group with different wind speeds under this rainfall intensity condition was relatively close.Secondly,indoor tests of sandy soil rainfall debris flow with and without wind action under different slope surface conditions were conducted.Comprehensive considering various factors such as soil movement characteristics,water content change rules and soil displacement clouds.The analysis of wind sensitivity of debris flow starting under four kinds of slope surface cases,such as bare slope,slope with geocells,grass slope,grass slope with geocells,shows that the geocells have the best protection effect.The wind response of the grass slope is obvious,and the starting of debris flow is delayed when there is wind and rainfall.When the slope surface is covered with geocell and grass at the same time,the effect of combining the two in the windless condition is worse than that of single geocell,and the effect of combining the two in the windy condition is better than that of single geocell.Finally,numerical simulations were conducted with the software of FLAC^3D.The starting mechanism of debris flow under the combined effect of rainfall and wind is analyzed from various aspects of soil movement characteristics,saturation and seepage field development characteristics.It was found that the direct effect of wind on the slope surface and the influence of rainfall seepage affect the starting of debris flow,causing increased damage to the slope during the starting of debris flow.The model is able to simulate the experimental phenomenon better in windless conditions and when the wind is small,but when the wind speed is large,the simulation is not satisfactory because of the software characteristics and the complexity of the combined effect of wind and rain in natural conditions.