Experimental Study On The Mechanism Of Loess-mudstone Landslide Induced By Heavy Rainfall In Tianshui Area

In the western loess plateau region of China,a large amount of loess layer is covered.Due to its special structural and water-sensitive characteristics,deformation and damage are severe under continuous or heavy rainfall conditions,resulting in a large number of disasters.In order to effectively reduce the losses caused by such geological disasters to the society and the people,it is of great significance to carry out experimental research on the landslide caused by rainfall.Based on the field geological mapping and engineering geological survey,this article took the rain landslides in Gangu County and surrounding areas of Tianshui,Gansu as the research object,carried out the basic physical properties test and mechanical property test of the landslide rock and soil body,and explained the slope from a micro perspective The internal causes of deformation and failure;through the large-scale indoor physical model experiment,from a macro perspective,analyze and study the law of water infiltration and deformation and failure characteristics of the slope under different prefabricated structural surfaces;based on Geostudio finite element numerical calculation software,the model experiment Numerical simulation calculations were carried out and compared with the model experiment results.The main findings are as follows:(1)The compression test of loess shows that the water content is a direct factor affecting the strength of loess.Compared with the natural undisturbed loess,its strength is greatly reduced in the saturated state,mainly represented by a decrease in cohesion and a small decrease in internal friction angle,which explains the internal cause of slope deformation and damage under rainfall.(2)The compression test and compression creep test of mudstone show that the damage of mudstone is mainly shear failure.With the increase of confining pressure,the fracture surface is smoother and straighter,and compared with the strength of natural mudstone,its long-term strength Greatly reduced,the ultimate strength is about 36%-53% of the conventional compression test strength.(3)According to the experimental and numerical calculation results,it can be concluded that the infiltration of water inside the slope has obvious regularity.The wetting front is basically parallel to the slope surface and the structural surface,and gradually expands to both sides;the infiltration rate at each location is different,specifically: structural surface> slope shoulder> slope foot> back edge> slope surface.(4)The destruction of loess-mudstone landslides with pre-existing rupture surfaces basically follows the prefabricated structural surface.The steeper the structural surface,the more severe the deformation anddamage,and the smaller the rainfall intensity required to achieve the damage.The deformation failure mode of the deformation is as follows: shoulder erosion and micro-fracture generation ? micro-fracture expansion and penetration ? local sliding failure ? overall sliding failure.(5)The loess-mudstone landslide with pre-existing structural surface has the following sliding mechanism: the slope in natural state along the old sliding surface,loess and mudstone contact surface,weak structural surface,maximum shear stress concentration zone,long-term slow creep deformation evolution,A penetrating potential sliding surface is generated inside the slope;under the action of rainfall,water penetrates into the soil,on the one hand,it increases the weight of the soil,on the other hand,it reduces the shear strength of the soil,when the shear strength of the soil is reached At the limit,the soil will shear and fail,and landslides will occur.