The Research On Failure Mechanism And Numerical Simulation Analysis Of Zonal Disintegration In Deep Tunnel

With the decreasing of shallow resources and developing of human living space, lots of planning and constructing underground engineering are becoming deeper. The roadways of mineral resources, tunnels of traffic constructions and caverns of hydropower have reached more than 1000m depth. With the increasing of underground engineering excavation depth, a series of new characteristic scientific phenomena appeared in the deep rock mass engineering. Zonal disintegration is nonlinear failure phenomenon which is completely different from the failure mode of shallow caverns, and the traditional continuum mechanics theory failed to give satisfactory explanation. The zonal disintegration in deep rock mass has become a hot and difficult issue in the field of geotechnical engineering today. So further study for the formation conditions, formation mechanism and influencing factors of zonal disintegration has important theoretical significance and engineering application value, and the study can provide important scientific basis for the development of deep mineral resources and construction of deep hydroelectric and transportation engineering in our country.Taking the deep tunnel of Dingji coal mine in Huainan mine area as engineering background, many true 3D geomechanical model tests were carried out under different conditions. These model tests were designed to reveal formation conditions and influence factors of zonal disintegration. Based on the strain gradient theory and continuum damage mechanics, the zonal disintegration elastic damage softening model and zonal disintegration energy damage failure criterion were put forward. Based on ABAQUS platform, the numerical analysis method of zonal disintegration was put forward. The numerical simulation of zonal disintegration was carried out under different conditions. The formation condition and failure mechanism of zonal disintegration was effectively revealed. In this article the main research contents are as follows:(1) Many true 3D geomechanical model tests in different conditions were carried out under high geostress. The influence of cavern shapes and stress conditions and soft interlayer on zonal disintegration in deep tunnel was studied. The formation condition and influence factor of zonal disintegration was revealed. The interval distribution of relatively complete zone and fracture zone in the surrounding rock was observed. The oscillatory change rule of radial displacement, radial strain and stress was illustrated.(2) The relationship between the strain localization and post-peak strain softening of rock and zonal disintegration was analyzed. The effect of strain gradient should been considered in the study of zonal disintegration. Based on the strain gradient theory and continuum damage mechanics, the zonal disintegration elastic damage softening model was put forward. The correlation between rock fracture and energy dissipation is analyzed. Based on strain energy density theory, the zonal disintegration energy damage failure criterion was established.(3) Eight-nodes hexahedron high order element considering strain gradient effect was constructed using Hermite interpolation function. The shape function and stiffness matrix of high order element was derived. Based on ABAQUS platform, the numerical analysis method of zonal disintegration was put forward, and the corresponding zonal disintegration program was developed. The zonal disintegration numerical simulation for model test was carried out. The results of numerical simulation and model test were basically consistent. The reliability of zonal disintegration elastic damage softening model and numerical analysis method was effectively confirmed.(4) Using the model test, theoretical research and numerical analysis, the failure mechanism of zonal disintegration was revealed. When the direction of maximum principal stress is parallel to tunnel axis and the value exceeds uniaxial compressive strength of surrounding rock, the zonal disintegration will appear. At higher axial stress, the stress in surrounding rock exhibits the oscillatory variation of peak and trough alternate. This is the key reason of zonal disintegration.