Active Characteristics And Fault Effect Of Deqin-zhongdian Fault Zone In Northwest Yunnan

With the development of railway in China,high altitude areas such as northwest Yunnan have also begun to plan and build railway,which has become an important part of transportation linking the corridor of northwest Yunnan.However,the topography and geological conditions in northwest Yunnan are extremely bad.The high mountain and canyon make most of the railway lines to pass through deep buried tunnels,and the development of active faults has become an important factor restricting the construction of railway lines.Therefore,it is very important to study the process dislocation effect of active faults in northwest Yunnan,and it is also of great significance to the prevention and control of engineering construction.In this paper,the Shangri-La to Deqin region of northwest Yunnan has drawn up the active faults along the railway as a detailed survey,determined the object,according to the field geological survey,survey data,The engineering geological characteristics of the railway line drawn up in Shangri-La to Dechin region are analyzed and studied.Through the study,the main results and understandings of the following points have been achieved:(1)The Shangri-La-Deqin railway line is located in the middle of the Hengduan Mountains in the northwest of Yunnan.The terrain and the landform are complex,and the mountains and the valleys are distributed in a staggered way.The geological structure in the region is complex and the whole is in the south-north direction.It can be seen that the region belongs to a strong extrusion zone and a tight-beam extrusion structure from the field of rock splitting and "S"-type.Since it is located in the southeast margin of the collision between the Eurasian plate and the Indian plate,the crustal activity is strong and the middle and strong earthquakes are multiple.Most of the faults in the Tertiary period have time-to-date inheritance activities.(2)The Deqin-Zhongdian fault zone in the study area is a intermittent right-handed strike-slip fault.There is no unified and continuous fault surface near the surface,and the connectivity is poor.Most of the faults occur in the form of extruded physical-chemical shear zone,and the small-scale compressive fracture zone is less.Combined with railway line location,it can be divided into three kinds of spatial distribution relations: railway line and fault parallel,railway line and fracture large angle intersection and railway line crossing fault discontinuity.(3)The numerical simulation results of three spatial relationships between railway lines and faults are drawn up.It can be seen that:(1)the influence degree of spatial position relation on tunnel: discontinuity of railway crossing fracture > intersection of railway and tunnel atlarge angle > parallel between railway and tunnel.(2)the parallel spatial relationship between railway and tunnel is due to the distance between railway and tunnel.Therefore,the influence is not large,and in the large angle intersection relationship between railway and tunnel,it is necessary to pay attention to the change of tunnel displacement near the fracture end.(3)in the spatial relationship between railway crossing fracture discontinuity,because of the distortion area of rock mass movement,It is easy to produce large displacement and stress concentration zone.The surrounding rock mass of the tunnel produced extrusion deformation of the tunnel for a hundred years.The displacement is about 0.14 m.In this case,the preventive measures shall be made in advance.