Hydrodynamic Mechanism For Shallow-slide Erosion Of Subalpine Meadow Soil And Its Spatial Prediction

The western Sichuan Plateau is a part of the mountainous areas on the edge of the Tibetan Plateau.The regional geomorphology is dominated by plateaus and alpine canyons,and the ecological environment conditions are extremely complicated,especially in the ecologically fragile areas where the agriculture,animal husbandry,and interlacing of mountains are characteristic.In the western Sichuan plateau,subalpine meadow soil is the main One of the soil types,widely distributed in the slopes of deep cut alpine valleys at an altitude of 4100 ? 4700 m,developed in the sub-humid climatic conditions of the plateau sub-frigid zone.The survey found that sub-alpine meadow soils in the western Sichuan plateau generally disintegrate in large areas and follow The weathered layer of particles produces slippery erosion,which causes severe soil erosion.Due to the fragility of the alpine meadow ecosystem,shallow slippery erosion often causes irreversible meadow degradation and bareness.Many domestic and foreign studies have been carried out.Investigation and research work on the erosion mechanism,erosion intensity and erosion amount of meadow soils in high latitudes and low altitudes.However,little attention has been paid to the serious erosion problems caused by such small shallow slips,and the corresponding space is lacking.Prediction method.This research involves hydrodynamics,hydrology,soil science,geotechnical mechanics,and ecology,etc.Therefore,it is of great scientific and practical significance to study the mechanism of shallow slip erosion of subalpine meadow soils and their risk prediction methods in the ecologically fragile key areas of the western Sichuan Plateau.In order to fully reveal the mechanism of shallow slip erosion of subalpine meadow soil and realize its risk prediction,first of all,through a large number of field investigations,fully grasp the structural characteristics of subalpine meadow soil in the western Sichuan Plateau and the geological prototype of shallow slip erosion.A series of soil and water parameters of the subalpine meadow soil were obtained by means of indoor density test,penetration test and direct shear test.Then,the indoor physical test was used to simulate the rainfall infiltration process of the subalpine meadow soil,and the analysis was carried out by monitoring data analysis.Mechanism of shallow slip erosion in sub-alpine meadow soil;finally improved the deterministic spatial prediction model-analytical solution of the safety factor of TRIGRS and coupled with the TOPMODEL model principle to predict the shallow groundwater level,and catalog the data by slip survey of field investigation Validate the model and establish an integrated risk prediction system suitable for shallow slip erosion of subalpine meadow soil based on Rosenblueth point estimation method,and carry out shallow slip of subalpine meadow soil with Xin Du Qiao Town as a typical object area Risk assessment of erosion.The main research results are as follows:(1)Based on field surveys and related data,the general characteristics of shallow slip erosion of subalpine meadow soils are summarized from the aspects of topography,rainfall conditions,soil structure,and geological structure,and the subalpine meadows are analyzed.Soil's composite erosion form with hydraulic and gravity effects.(2)The indoor soil samples of sub-alpine meadow soil samples were measured using indoor testing.The average natural density of the meadow soil was 1.477g/cm3,and the average natural bulk density was 14.77KN/m3.The cohesion of the subalpine meadow soil is 2.13 Kpa and the internal friction angle is 33.2°;in the saturated state,the cohesion of the subalpine meadow soil is 2Kpa and the internal friction angle is 26°.The alpine meadow soil permeability coefficient is 0.0166cm/s,and the subalpine meadow soil weathering layer permeability coefficient is 0.0028cm/s.(3)A geological model constructed according to the characteristics of slippery erosion,conducted a physical test of shallow slippery erosion of subalpine meadow soil in the laboratory,and monitored the data of soil moisture content,soil pressure,pore water pressure and displacement,The shallow slip erosion of subalpine meadow soils and groundwater levels and rainfall forms are analyzed,and the process and mechanism of shallow slip erosion of subalpine meadow soils are summarized.(4)The analytic solution of the infinite slope model is revised considering the influence of osmotic pressure;the theory of the topographic index in the TOPMODEL is combined with the slope stability analysis method to establish a shallow slip for subalpine meadow soil The theoretical model of erosion,using the new conceptual model to optimize the parameter input and result output of the TRIGRS model.(5)Using TRIGRS to analyze the stability of meadow soil slopes in the target area under three conditions of rainfall intensity 2.5mm/h,7.5mm/h and no rainfall,simulated slippery erosion danger area and data items recorded on site survey In the GIS environment,the relationship between rainfall intensity,terrain slope and the risk of shallow slippery erosion of sub-alpine meadow soil is summarized: with the increase of rainfall intensity,the area of slippery erosion danger area increases;the danger area and the more dangerous area It is mainly concentrated on gentle slopes of 5-15° and steeper slopes of 15-25°,which mostly occur around river valleys or at steep and gentle junctions.(6)Take the two independent parameters of rainfall intensity and stratum thickness as random variables,and use the Rosenblueth point estimation method(statistic moment method)to analyze the reliability of the slope.Use the grid calculator of Arc GIS to calculate the object Visualization of the probability of slippage in the area It is highly consistent with the area of safety factor less than 1.2 in TRIGRS,reaching 74.86%.