Study On Surface Erosion Characteristics And Microscopic Mechanism Of Loess

Loess,as a special granular material,has some special properties,such as loose porosity,vertical joint development,strong water sensitivity,etc.,leading to frequent gullies and geological disasters in the Loess Plateau due to the interaction between water and loess.Based on the field investigation,this paper takes the typical loess geological disasters in the Luliang mountain area of western Shanxi Province as an example to analyze and summarize the relationship between loess hydraulic erosion and the geological disasters of collapse and landslide in western Shanxi Province.It is found that surface erosion is the main form of hydraulic erosion in the formation of geological disasters such as collapse and landslide.Slope and water content variables were designed to simulate the physical erosion of loess surface erosion to analyze the influence of each variable on loess surface erosion and reveal the characteristics of loess surface erosion.The special properties of loess are closely related to its microstructure.On the one hand,the extensive pore structure and joints in loess provide water migration channels and infiltration paths.On the other hand,there are a large number of soluble substances and clay minerals in loess composition,which easily interact with water and directly affect the hydrological properties of loess.Therefore,this paper analyzed the main microscopic fabric and contact mode of loess according to the electron microscope image,and then established a scientific numerical simulation conceptual model based on the loess microstructure to conduct numerical simulation analysis of loess surface erosion.The process and stage characteristics of loess surface erosion were inverted and the microscopic mechanism of loess surface erosion was summarized based on the physical simulation results.The main research contents and achievements are summarized as follows:During the formation and evolution of loess collapse and landslide geological disasters in western Shanxi,hydraulic erosion mainly promoted the occurrence of disasters through three aspects: shaping the geomorphic conditions,shaping the topographic conditions and changing the stratigraphic structure.There are three types of erosion,namely slope erosion,gully erosion and cave erosion,which are accompanied by surface erosion.In the physical simulation test of loess surface erosion,soil erosion rate increases with the increase of water content.With the increase of erosion slope,the erosion rate increases first and then decreases,and reaches the maximum value trend at 30°.According to the changes of soil samples recorded in the process of erosion,the loess plane erosion process can be divided into three stages: micro-channel erosion stage,gully erosion stage and collapse failure stage.The characteristics of stage erosion and microscopic mechanism of loess are analyzed.According to the microscopic images of the scanning electron microscope,the structure forms of the main units of the loess microfabric and the spatial contact modes of the loess skeleton particles were obtained.Based on the above micro-structural characteristics of loess and the chemical and mineral components of loess,the connection between the loess skeleton particles is assumed to be the link linkage,among which the link linkage of clay minerals and the chemical linkage of soluble salt have a great influence on the loess planar erosion.Based on this,a conceptual model of numerical simulation is established.The degradation law of link link and its realization process in PFC are given.The PFC numerical simulation was carried out through the conceptual model established above.The water head difference in the numerical simulation was set as 600,700 and 800 pa respectively according to the flow shear force in the physical simulation.The results obtained from the numerical simulation are consistent with those obtained from the physical simulation,and the process of loess plane erosion is divided into three erosion stages,namely,the micro-channel erosion stage,the gully erosion stage and the collapse failure stage.The results invert the whole process of loess plane erosion.It is also revealed that the microscopic mechanism of surface erosion of loess is a process in which the cement in loess dissolves in water or destroys,which separates the loess skeleton particles and then migrates and removes the soil under the action of water flow,resulting in the change of slope surface morphology.