Study On Deformation And Instability Mechanism And Stability Control Technology Of Tuff Tunnel Under High Geostress

In this paper,relying on the project of Ailashan Highway Tunnel,by means of field investigation,theoretical analysis,regression analysis,numerical analysis and field test,the influencing factors,failure mechanism and deformation control technology of large deformation in tuff section of ailashan highway tunnel are systematically studied,the main conclusions are shown as followed:(1)Through the investigation of large deformation and failure in the construction site,monitoring data analysis and theoretical analysis,it is concluded that the failure characteristics of tuff large deformation section mainly include:large deformation,fast deformation rate,long deformation duration,concentrated dominant parts of deformation,and large deformation has the characteristics of squeezing large deformation without collapse.The main influencing factors of large deformation failure are:initial high ground stress field,weak tuff,construction method,support measures and groundwater,etc.(2)Based on the measured values of the hydraulic fracturing method of the Ailashan Highway Tunnel,the three-dimensional geological model of the tunnel is established by combining the numerical simulation and regression analysis.The linear regression equation of the initial stress field of the tunnel is obtained,and the value and distribution law of the ground stress along the axis of the tuff section of the tunnel are explored.(3)Based on creep effect,the excavation deformation law of tuff section of the tunnel is proved,and the large deformation grade of the tunnel is divided.(4)Based on the investigation of the support parameters and deformation control technology of typical soft rock tunnel with large deformation at home and abroad,the support parameters and deformation control technology of the constructed section with large deformation are summarized,and the key technology of the support parameter optimization of the project is obtained.The suitable support scheme for the large deformation section of tuff is selected by using the research methods of numerical simulation analysis and field verification.The influence of different excavation methods on tuff surrounding rock under high geostress is studied by numerical simulation.The results show that the two-step reserved core soil method is more suitable.(5)On the premise of support safety,this paper puts forward the recommended limit displacement value of large deformation section of Ailashan Tunnel,and puts forward the reserved deformation amount of different levels of large deformation,and establishes the monitoring deformation management level standard of large deformation section,so as to determine the stability and safety of support structure,and effectively guide the construction.The above research results have been well applied in the construction of tuff section of Ailashan Highway Tunnel,and the large deformation problem of tuff section has been successfully treated,which ensures the construction quality and safety of the site,and can provide reference for similar projects.