Study On Stability And Scheme Optimization Of Tunnel Weak Surrounding Rock-support Structure

With the continuous development of highway and railway tunnel construction in our country,the weak rock tunnel support structure design and construction of face stability problem is very outstanding because of its weak surrounding rock tunnel of intensity difference caused by large deformation of surrounding rock deformation duration long deformation speed,the serious influence of tunnel construction period,the supporting structure damage to the tunnel instability may occur even dangerous accident is the main reason of the above problems,such as understanding of weak rock tunnel deformation mechanism,deformation law,there is no feasible control method.In view of the above problems,on the basis of previous research results,the failure characteristics of the support structure in the field are analyzed,and the influence on the deformation of the jointed soft rock tunnel is discussed.The mechanical properties of mudstone are analyzed by sampling the rock and uniaxial compression test.Based on the Hoek-Brown criterion,the quantitative GSI surrounding rock rating system is connected with the macroscopic continuum theory,and the Hoek-Brown parameter is transformed into the Mohr-Coulomb parameter.Based on the convergence-constraint method,the interaction curve of surrounding rock-supporting structure is obtained,and the stability of the soft surrounding rock-supporting structure is analyzed.Based on the theory of incomplete arch effect and the principle of new idea method,the optimal supporting structure design scheme is put forward.Through field monitoring and analysis,the reliability of optimized support scheme is verified and the following important conclusions are drawn:(1)To Yangmeishan tunnel in the early period of weak surrounding rock supporting structure analysis,the characteristics of tunnel primary support steel frame deformation,the early concrete cracking,steel mesh,-support in weak rock tunnel structure instability of joint action by multiple factors,main factors include the strength of the surrounding rock,the size of the supporting time and initial support resistance.The lower the strength of surrounding rock,the lower the deformation of surrounding rock.The later the supporting time is,the greater the surrounding rock deformation is.The larger the support resistance,the smaller the surrounding rock deformation.(2)According to uniaxial and triaxial compression tests,the uniaxial compressive strength of mudstone is relatively low,showing brittle failure,and the uniaxial compressive strength ranges from 9 to 15 MPa.The characteristic curve of surrounding rock-supporting structure isconstructed,and it is concluded that the safety factor of tunnel at arch roof and arch shoulder is low,and the surrounding rock of tunnel is prone to deformation.(3)Principle based on the new method and theory of incomplete arch effect,optimize the Yangmeishan tunnel supporting structure design,analysis of preliminary constraints and the pre-reinforcement measures in control surrounding rock deformation effect is better,so the reserve increasing deformation,glass fiber and anchor pipe roof in advance on the pre constraints and prediction of tunnel reinforcement measures,through the surrounding rock-supporting structure characteristic curve,the supporting structure optimized design scheme has a good stability.(4)Through field monitoring of Yangmeishan tunnel analysis shows that in situ observation results show that the front section of surrounding rock for mudstone,poor lithology,and based on the displacement of surrounding rock,stress of surrounding rock,and steel frame internal force monitoring,with the excavation of the tunnel,the tunnel vault and large distortion of left,right shoulder,the surrounding rock pressure is bigger also,the largest steel pressure also appears in the vault,but displacement in the allowing range of deformation,in soft rock area shows that optimized support scheme to succeed.