Study On Failure Modes And Stability Of Unloading Zone Of Slopes In Alpine-Gorge Region Along Sichuan-Tibet Railway

The western Sichuan and Hengduan alpine-gorge region that Sichuan-Tibet Railway pass through experienced strong tectonic movement that lead to broken stratum,highly development of unloading zone of slope.This kind of slope unloading zone is large in scale and widely distributed,which is very unfavorable to the stability of slope rock and soil mass.It is a high-risk area for many types of geological disasters,and it poses a great potential threat to the construction and safe operation of railway.Therefore,it is particularly important to study the failure modes and stability of the slope unloading zone in alpine-gorge region along Sichuan-Tibet Railway.In this paper,the on-site geological survey is used as the main means to carry out a detailed investigation of geological conditions,development characteristics,rock structure characteristics and signs of deformation of the slope unloading zone in this study area;The develoment depth of the slope unloading zone in some hydropower projects is calculated by summarized the references,then the development and distribution rules of the slope unloading slope in this area are summed up;According to the structural features and signs of deformation of the rock slope in unloading zone,failure modes of slope unloading zone is proposed;At last,the stability of a typical slope unloading zone is analyzed by the combination of qualitative analysis and quantitative analysis.The contents and results of the specific research are as follows:(2)The study area is located on the southeastern edge of the Qinghai-Tibet Plateau.The geological background is complex,and the geological composition and structural pattern are quite unique.The strata in every era are exposed,the tectonic deformation is complex and the new tectonic movement is strong.The complexity of strata,structures and geomorphology lead to the complexity of hydrology condition.(2)Through the field geological survey and through the means of remote sensing interpretation,the development characteristics,distribution ranges,rock structure characteristics and surface deformation signs of the deep unloading zones of the study area are investigated and analyzed in detail.The results show that the slope unloading zone along the Sichuan-Tibet Railway is extention.(3)The development depth of unloading zones at different elevations of some hydropower engineering slopes in the study area was calculated,and a certain basic rule was initially obtained.Generally,the development depth of the slope unloading zone is deepened with the increase of elevation.The development of the slope unloading zone is influenced by the morphological characteristics of the slope,the lithology of the strata,the characteristics of the rock mass structure and the initial geostress environment,and the weathering characteristics of slope rock mass et al.(4)The deformation and failure of the surface of the slope unloading zone in the study area is investigated in detail.At the same time,the data of the deformation and failure of the footrill in the unloading zone of slope are collected.combined with the development characteristics of the rock structure,the deformation and failure modes of the slope unloading zone in the slope unloading zone are divided into five categories:the dumping,plane sliding,stepped sliding,collapse and sliding of loose deposit.(5)The stability of the slope unloading zone of the bridge site under the bridge site of the Sichuan and Tibet railway is analyzed by using the macroscopic geological qualitative analysis,the rigid body limit equilibrium method and the finite difference method.The stability analysis shows that the slope unloading zone is stable and stable under the natural condition.The stability of the slope decreases slightly under the heavy rain condition,but it is still in the basic stable state.Under the earthquake condition,the stability is greatly reduced,and it is in the under-stability and unstable state,which may result in the instability failure.