Study On The Regularity And Mechanism Of Large Landslides In Longnan Mountain Area

Geological disasters occur frequently in western China,and the high mountains and deep valleys in the mountains of Longnan have created a unique geological environment for geological disasters.The high incidence of landslide in Longnan mountain area causes a lot of human resources and financial loss every year.In order to find out the regularity and mechanism of landslides in Longnan mountainous area,this paper selects large and giant landslides as the research object,and based on the original geological survey data,the landslide data were further verified,corrected,supplemented and counted to reveal the law of mass occurrence of large and giant landslides in the study area.Combined with field surveys,indoor scanning electron microscopy,XRD test and numerical simulation,and taking Qinyu fault as an example,the regional stress field characteristics,engineering geological characteristics of the fault zone and the stress state of the upper and lower walls of the study area are analyzed,exploring the mass occurrence mechanism of fault zones and earthquake-induced landslides,from the perspective of in-situ stress.This article draws the following conclusions:(1)Large and giant landslides in the Longnan Mountainous Area are generally distributed linearly along both sides of the regional fault zone,but the scale of the landslides,the number of landslides,and the concentrated development areas vary depending on the fault zone.(2)The distribution of large and giant landslides in the study area is positively related to the seismic intensity and the peak acceleration of ground motion.There are a large number of large-scale landslide instability records in the study area during the earthquake active period and the earthquake calm period,but the number of unstable landslides hit the peak point during the seismic calm period,indicating that the landslide has a lagging development feature.(3)The hanging wall stress of the Qinyu fault is more concentrated than the footwall.The interval between the rock mass structural planes on both sides of the Qinyu fault has a regular change that increases away from the fault zone,and the range of change has a positive correlation with the corresponding fault width.Compared with the lower plate,the variation of the distance between the structural planes of the rock mass on the fault zone is larger,and the occurrence changes more severely.Fractured rock mass structure,highly concentrated stresses on both sides of the fault zone,and the stress concentration on the hanging wall cause the landslides in the study area to be distributed along the fault line in a linear manner.(4)Tectonic faults cut slopes on a large scale,divide the landslide boundaries and bodies,forming the basic spatial pattern of landslide mass distribution.Based on this,the continuous accumulation of in-situ stress on the upper wall of the reverse fault exacerbates the destruction of the structural integrity of the upper rock mass and breaks the mechanical balance of the landslide,which leads to the instability of the landslide.The clay content and various ingredients of clay in the fault mud also indicate that the fault zone is likely to continue to move.(5)The regional stress field releases in-situ stress in the form of earthquakes,resulting in the mass distribution of landslides.In general,the greater the value of in-situ stress,the higher the seismic intensity and the greater the number of landslides.The combined seismic effects have caused mass earthquake landslides in the study area.The inversion results of the in-situ stress field indicate that the stress on both sides of the fault zone in the study area is relatively concentrated,and the stress at the intersection and turning point of the fault is highly concentrated.