The Prediction Of Rock Burst,Large Deformation And Their Risk Assessment For Erlang Mountain Tunnel Sichuan-Tibet Railway

The terrain conditions and geological structure in the western region of China are very complex.It is inevitable to use the deep buried long tunnel In the construction of highway and railway.Chengdu-Chengdu to Lhasa railway xinduqiao section from east to west in general terrain lift sharply.Tectonic genus Yangtze Block and Qiangtang-Sanjiang orogenic belt,the North-East Longmen Shan tectonic belt,north-south Chuandian tectonic belt and NW Xianshuihe structural belt formed the famous "Y" shaped configuration in western China,Line is located the thrust wedge portion of "Y" shaped configuration.Frequent earthquakes and strong new tectonic movement in the region,"Y" type structure of the intersection of the Erlang mountain near the high stress problem is particularly prominent.New Erlang Mountain Tunnel Surrounding Rock in soft and hard rocks were widely distributed,hard rocks like limestone,quartz sand,quartz powder sandstone,granite,flash diorite,andesite;soft rocks like mudstone and shale.And faults,fault development,fault zone in the broken rock,fracture zone width,which influence the bandwidth,along with rupture of the visible a lot of cataclasite and mylonite,forming strong compressional fracture zone.From the previous survey data,the estimate is that since the deep buried depth of tunnel,high geo stress,hard rock is easy to produce rock burst,soft rock and fracture,fault fracture zone,such as weak zone and surrounding rock is easy to produce large deformation,the future tunnel construction is likely to face very serious rockburst and large deformation disaster.Therefore,it is urgent to carry out special research on in-situ stress and rock burst and large deformation,so as to provide scientific basis for the selection and feasibility study of railway.First,according to preliminary survey data tunnel,Combined with the measured results of a nearby highway tunnel,Using FLAC numerical analysis software,Inversion of mountain railway tunnel of ground stress field are analyzed,The results show that:(1)The in-situ stress shows an increasing trend with the increase of the depth of the buried depth;(2)The fault has a certain influence on the stress field near the fault,it has the stress reduction and the concentration phenomenon,the stress of the fault zone is reduced,and the local high stress zone is formed on both sides of the fault zone;(3)At both ends of the tunnel shallow buried section and the maximum principal stress is nearly horizontal direction,stress value gradually from low to high,show that the stress field is to the level of stress of tectonic stress field,with the depth increased to a certain depth,vertical stress become maximum principal stress,formation stress field based on the superposition of gravity field and tectonic stress.Through comprehensive analysis of geological and extension method,were predicted to tunnel rock burst,large deformation,due to differences in different strata lithology,buried depth,stress and so on all aspects of factors,different segments of tunnel rock burst,large deformation also has the difference.Therefore,the segmentation of the tunnel rock burst,large deformation prediction,and come to the conclusion :(1)Tunnel without rock burst length 8726 m,accounting for 60% of the total length of the tunnel;slight rock burst length of 1157 m,accounting for 8% of the total length of the tunnel;medium rock burst length 3628 m,accounting for 25% of the total length of the tunnel;strong rock burst length 1050,accounting for 7% of the total length of the tunnel.(2)Tunnel without large deformation segment length 11206 m,accounting for 77% of the tunnel length of;slightly large deformation segment length 873 m,accounting for 6% of tunnel length of;medium large deformation segment length 2179 m,accounting for 15% of the tunnel length;the strong large deformation segment length 303 m,2% of the total length of the tunnel.Based on the rock of Erlang Mountain Tunnel railway burst,large deformation and serious possibility analysis,On the basis of this,the risk grade of rock burst and large deformation is calculated.Results show:(1)Erlang Mountain railway tunnel rockburst Risk Assessment: Low risk level rockburst total length of 8229 m,57% of the total length of the tunnel;moderate risk rating rockburst total length of 1637 m,11% of the total length of the tunnel;the height of the level of risk of rock burst total length 3628 m,25% of the total length of the tunnel;a high level of risk rock burst total length of 1050 m,accounting for 7% of the total length of the tunnel.(2)Erlang Mountain Tunnel railway large deformation Risk Assessment: Low risk level large deformation total length 10201 m,accounting for 70% of the total length of the tunnel;moderate risk level large deformation total length 1861 m,accounting for 13% of the total length of the tunnel;large deformation at high risk rating total length of 2482 m,17% of the total length of the tunnel.