Study On The Stability Of Surrounding Rock Of Jiudingshan Long Tunnel On Xinchu-Daqing Expressway

With the implementation of the national"13th Five-Year Plan"strategy and the strong promotion of the"One Belt and One Road",the western mountainous highways have developed rapidly.The stability of the surrounding rock of deep-buried long tunnels not only affects the suitability of tunnels and the cost of tunnel construction,but also has a close relationship with the safety and duration of road construction.The stability of surrounding rock is becoming the research core of deep-buried long tunnels and the high-speed road construction of the mountains.Therefore,the paper obtained detailed geological survey data through the engineering geological survey of Jiudingshan Tunnel.Based on a systematic and detailed field survey,the influencing factors of wall rock stability were analyzed in depth and analyzed from a qualitative,semi-quantitative and quantitative perspective.The stability of tunnel surrounding rock was evaluated using field tests,BQ classification of surrounding rocks,and numerical simulation of finite element method.The main research results obtained were as follows:The engineering geological conditions of the Jiudingshan tunnel are analyzed in detail.The Jiudingshan tunnel is located in the near-NW-direction of Red River-Erhai deep fault and nearly-SN-direction of Chenghai-Binchuan fault.The geological structure is extremely complicated,the rock body is broken,the groundwater activity channel develops,and the karst water and granite porphyry cracked water is easy to enrich.The granite porphyry is mostly exposed in the tunnel entrance,accompanied by altered limestone,the rock body is extremely broken,and the tunnel self-stability is poor;most of the sand shale is exposed at the exit of the tunnel and is affected by the Xiangyang anticlinal.The diabase and gabbro were irregularly invaded and the rock body was extremely broken.Using the rock mass corrected quality index value BQ and the modified[BQ]classification,the percentages of the total length of tunnels in Grade V surrounding rock,Grade IV surrounding rock,and Grade III surrounding rock were 39.5%,48.9%,and 11.6%,respectively.Based on the study of the stability of the surrounding rock by various influencing factors,the type III surrounding rock of the tunnel is mainly dolomitic limestone intercalated with dolomite,which is of good quality and hard quality.It is affected by the geological structure and has high local stress.The surrounding rock stability is good.The intrusion of granite porphyry,diabase,gabbro and other rock bodies and geological structure have a greater influence on the V-type surrounding rock and part of the IV surrounding rock.The fissures of surrounding rock joints are densely developed.The crushing part of the rock mass is sand-like and presents a crumb stone structure,which results in poor stability of the surrounding rock and susceptibility to collapse.Support should be strengthened in time.At the same time,the in-situ stress measurement was performed on the tunnel hole SZK60-3,and the test data was analyzed:the horizontal stress in the shallow part of the tunnel was not dominant,the vertical self-gravity stress was dominant,the type of the ground stress belonged to?_V type,and the tunnel axis direction was 287°.The direction of the maximum principal stress is 349°,and the angle between the two is 62°,which is beneficial to the stability of the surrounding rock of the tunnel.Using MIDAS/GTS geotechnical analysis software,the deformation laws of tunnel roof settlement,floor uplift,and horizontal convergence of tunnel walls were obtained.Through bolt support and shotcrete,the deformation of the displacement field and stress field in the numerical simulation is controlled within the safety range,and the stability of surrounding rock is improved,which can meet the construction safety requirements.