Research On Relevant Probloms About Failure Mechnism Of Surrounding Rock In Deep Buried Tunnel

In China, more and more long-large-deep tunnel appears, even tunnel group, fast construction and the forecasting and controlling for the disasters caused by surrounding rock mass such as rock burst has becoming the major task for tunnel construction. But researches on the failure mechanism of surrounding rock are still not matured owing to complex and uncertain geology in tunnel, and the current study, thinking little of the failure process, mostly focuses on stress condition and failure criterion.Funded by"research on the stability and reliability of tunnel and underground space structure"(a key project of National Nature Science Foundation of China) and taken Chongqing Tongyu tunnel as an engineering example, this paper dicussed the failure mechanism of surrounding rock in deep buried tunnel from the microscopic damage mechanics and fractal theory. And meanwhile, tunnel in-situ-stress was tested and simulated. Rock burst, a familiar brittle fracture of hard rock in deep-buried tunnel, was forecasted by using BP neural network. From the research, the following conclusions were achieved:(1)From research on damage property of tunnel surrounding rock by using RFPA^2D, a software based on microscopic damage mechanics, it was found that hard rock mass in deep buried tunnel tensilely fractured firstly at the roof, then at the spandrel, and finally extended to the deep level. At the same time, rock fracture, mainly in the form of splitting for limestone under un-axial compressing conditions, evolved four steps from being pressed to denser, elastic deforming, damage localizing and perforation of fractured elements, which were homologous to the four steps of stress strain curve, the damaged rock showed a characteristic of non-linear and localizing, and AE account reflected the damage degree of rock.(2)Self-similarity in time and space of failure process was obtained from research on fractal characteristic of surrounding rock in deep buried tunnel. A method of estimating failure degree by fractal dimension was brought forward. From the data and photo obtained in situ investigation, the fractal dimension of surrounding rock in Tongyu tunnel was computed by manual work and the software Fractalfox2.0 based on box accounting method, and found that space dimension Ds (s=0,1,2,3,one dimension to three dimension separately stands for point, string, area, and body) is equal to the sum of fractal dimension D_f, and damage variable D , i.e. D = D_s - D_f.