Study On Stability Of Surrounding Rock In Deep Buried Hard Rock Tunnel

The risk of rock burst will be higher and more nonlinear effect is manifested in the surrounding rock with the ground stress increased gradually because of the tunnel buried depth increasing. With special nonlinear mechanical behavior significant, the traditional theory for rock mechanics faces a new challenge.This research work is being supported by grants from National Science Fund for Distinguished Young Scholars of China (NO.50625824). The secondary stress after excavated, a very important influencing factors for the stability of surrounding rock is studied. Rock burst, a familiar brittle fracture of hard rock in deep-buried tunnel, is forecasted using the method of optimal relative membership degree based on the maximum entropy principle. And meanwhile, the creep characters of surrounding rock and supporting structure are researched. The nonlinear characteristics in construction process of hard rock deep tunnel namely the relationship between energy dissipation and stability of surrounding rock are analyzed by means of nonlinear dissipative scientific theory.The main work and research conclusions are as follow:?An improved stress restoring method based on the historical stress restoring method is discussed. And the principle of improved stress restoring method is that: calculation the strain variation of the three directions; then restoration the secondary stress; calculation the secondary stress(?_x??_zand?₄₅) according to the pressure based on strain variation. The key coefficient of improved stress restoring method, equivalent coefficient, is obtained by laboratory test and numerical experiments. It is discussed the relationship between the rock mechanics parameters, cofining pressure and equivalent coefficient, and its feasibility and rightness are tested by field practice.?Secondary stress of hard rock tunnel sections is obtained by field test through improved stress restoring method. And the results are compared with that of elastic mechanics method. It is discussed that there is a relation between excavation distance and principal stress of surrounding rock, the influence scope of plane stress and shear stress to correct the improved stress restoring method. Furthermore, the principle how the ground stresses variation effect of stress field in some sections of tunnel has been studied.?The prediction standards of rock burst are selected including the conditions of mechanics?integrity?energy and brittle on the basis of the analysis rock burst criterion prediction at home and abroad. The concept of relative membership degree on the rock burst prediction was introduced. The weight of standards and fuzzy matrix of relative membership degree are calculated. Uncertainty in rock burst prediction is described and compared according to the information entropy. Generalized to weighted distance is also defined to characterize the differences in rock burst Based on the maximum entropy principle, the establishment of a rock burst prediction fuzzy optimization model. The results from the application to practical example and comparisons with other methods are fairly good. And the prediction model is applied in putaoshan tunnel and the predictions are consistent with the actual rock burst. Furthermore, it is discussed the ralationship between the random error-weight and predict results.?The triaxial compression creep test on supporting structure and micritic dolomite of the deep tunnel concrete specimens is performed by using the MTS-815 hydraulic servo system. A combined viscoelastic plasticity model is developed after the characteristics of concrete creep deformation were analyzed, which can be used to describe the creep behavior and whole creep process of the deep tunnel support structure. The combined model is characterized by a visco-elasto-plastic deviatoric behavior and an elasto-plastic volumetric behavior. The viscoelastic constitutive law corresponds to a Burger model, and the plastic constitutive law corresponds to a Mohr-Coulomb model. The characteristics of viscoelastic plasticity can be described by the combined model. The problem which the typical Burgers model was only can be used to describe viscoelasticity creep is resolved perfectly. In addition, the methods to solve triaxial compression creep model parameters are given and the parameters of supports for deep tunnel are determined to analyze the stability of surrounding rock.?Shear strain time series of several typical points which placed in the tunnel at deep hard rock location are selected to reconstruct phase space. Some nonlinear dynamics indexes (largest Lyapunov exponents and Kolmogorov entropy) are calculated to study the deformation heterogeneity in evolution process of excavation and the nonlinear stability of surrounding rock. And the evolution of surrounding rock system at chaotic state is sensitive to initial conditions.?The deformation features of surrounding rock in deep hard rock tunnel are analyzed after long-term monitoring measurement. It is fund that the deformation features are different greatly from shallow tunnel. By applying whole domain method,local region method and mixed optimizing model(chaotic reconstruct phase space mixed with Gray Model)to the engineering, the deformation of surrounding rock is predicted and the results of these displacement-predicting models agree well with the measured results. In addition, analysis is made about the comparison prediction results with every method to discuss the comprehensive error and precision.