Study On Disaster Mechanism And Movement Characteristics Of Zhonghai Village Landslide In Xigeda Formation,Hanyuan

On August 21,2020,a sudden geological landslide occurred in the Xigeda Formation of Zhonghai Village,Hanyuan County,which resulted in significant fatalities and property damage.In this paper,on the basis of the identification of the development characteristics of the landslide,the characteristics of the water-softened and greatly reduced shear strength of the hemigeda Formation in Hanyang Yuan were studied by using the laboratory geotechnical experiments.Combined with the X-ray diffraction test and the scanning electron microscope test,the qualitative and quantitative microscopic characteristics of the water-collapsed hemigeda formation were investigated from the microscopic perspective.The Seep/W module of Geo-Studio is used to study the infiltration rule of Zhonghai landslide under the action of rainfall,and the formation conditions and genetic mechanism of the Hanyuan landslide are analyzed in detail from two aspects of the special hydrological properties and rainfall of the Xigeda formation in water disintegration.Then the numerical simulation software Massflow was used to reproduce the movement process of Zhonghai Village landslide,and its movement characteristics were analyzed.The main conclusions are as follows:(1)By comparing the mechanical properties of the hemigetic rocks of the Xigeda Formation under natural and saturated conditions,it is found that the C value and "φ" value of the hemigetic rocks of the Xigeda Formation of the Hansyuan Formation decrease by34.87% and 42.19% under saturated conditions,which indicates that the hemigetic rocks are significantly influenced by water and have high water sensitivity.In the semi-diagenetic mineral composition of Xigeda Formation in Han Yuan,quartz occupies the largest mass ratio,followed by illite with mass ratio of 40.9% and 19.0%,respectively.The main waterabsorbing mineral is montmorillonite.(2)The "disintegration" of the "group" particles leads to the collapse of the particle skeleton,the pore structure changes significantly,the pore diameter decreases significantly and the number increases significantly.At the same time,the number of large-diameter particles decreases significantly,the number of small-size particles increases significantly,more particles tend to be round,the orientation probability entropy increases,and the arrangement of particles becomes more disorderly.Structural stability deteriorates.Compared with the natural state,the overall structure of the semi-diagenetic rock becomes looser and the structural integrity becomes worse,which shows the mechanical property that the shear strength decreases obviously in the saturated state.According to the grey correlation degree analysis,it is found that the macroscopic strength parameters of hemidiagenesis,such as cohesion C and internal friction Angle "φ",have good correlation with the mean particle diameter,mean particle circularity,particle orientation probability entropy,fractal dimension of particle distribution and fractal dimension of particle morphology,among which the correlation degree with the mean particle diameter is the highest.(3)Under rainfall conditions,rainwater first penetrated into the overlying slope residual layer and then into the lower Xigeda Formation.After the rain stopped,the rainwater infiltration process continued.During the whole rainfall process,the volume water content at the gentle slope platform Ⅲ reached saturation first,the groundwater level began to rise first,and the rain dissipated the slowest.In the whole simulation process,the safety factor of the slope has been declining.Three days after the rainfall basically stopped,the safety factor of the slope was still declining,which reflects the lag of the influence of rainfall on the landslide stability.(4)The simulation results show that the duration of the whole landslide is 100 s,and the maximum accumulation thickness is located on both sides of the S435 provincial highway at the landslide front,which is consistent with the actual situation on site.In the whole movement process,the maximum velocity appears at the shear outlet in the loading slip zone and the steep ridge above the dart S435.The reason for the occurrence of these two velocity peaks is the change of terrain.The deformation and failure mechanism of Zhonghai landslide is creep slip-pull slip-loading slip-scraper accumulation.The sliding surface is basically the same as the dip Angle of the rock layer,which is a bedding bedding bedding landslide.