Three-dimensional Refined Constitutive Theory Of Rock Mass And Its Integration In Stress Control-based Design And Analysis Of Deep Tunnel

Marching into the deep earth is a strategic scientific and technological problem that must be solved.The intelligent construction of deep-buried rock tunnels is an important development trend of tunnel engineering construction nowadays.Refinement of data collection,precise analysis,and accurate control are the core contents of intelligent construction,and also the main technical bottleneck restricting the efficient and safe construction of deep-buried tunnels.The traditional calculation model does not reflect the mechanical characteristics of deep-buried rock mass,and the calculation parameters of the model are mainly determined by laboratory rock mechanics test or back analysis by field deformation.There is a lack of methods for real-time,rapid,and dynamic acquisition of rock mass parameters,and for three-dimensional（forward）analysis and dynamic design.At the same time,the existing tunnel engineering design ideas are mainly based on the control of deformation（deformation control）,ignoring the mechanism of the process control（stress control）of the stress release and transfer of surrounding rock during the excavation of deep tunnels.The stability calculation theory and design analysis method of deep-buried rock mass are facing new major challenges.Given the above problems,theoretical analysis,numerical simulation,and experimental tests were used to study the three-dimensional and nonlinear strength characteristics and mechanical behavior of deep-buried rock mass under high stress and complex stress conditions.Based on digital in-situ test,the mechanical parameters of rock mass were obtained,and the three-dimensional（forward）analysis and dynamic design of rock mass engineering were carried out.The three-dimensional design analysis theory and"stress control"design analysis method of deep-buried rock tunnels were formed.The main results of this study include:1.A smooth GZZ three-dimensional strength criterion and post-peak dilatancy angle model for deep rock mass were proposed（a）Strength theory of deep rock mass（smooth GZZ strength criterion）.For the non-smoothness and non-convexity of the original generalized Zhang–Zhu strength criterion（GZZ）,a smooth GZZ criterion was proposed by modified the original GZZ,and the smoothness proof and full convexity condition of the new criterion were given.Using 15 sets of true triaxial experimental data collected in literature,the fitting accuracy and reliability of the new criterion were analyzed,and its applicability in the deep rock mass was also discussed.（b）Post-peak dilatancy model of the deep rock mass.Aiming at the shortcomings and application limitations of the existing rock dilationcy angle model,such as many parameters and difficulty in applying to deep rock mass,a post-peak dilation model with a simple form,few parameters and clear physical meaning was proposed considering the effects of confining pressure and plastic shear strain.The method of extracting the dilatancy angle based on the complete stress-strain curve was given,and the fitting accuracy and applicability of the new dilatancy angle model were analyzed by using different types of rock dilatancy angle data.According to the dilatancy angle data of the intact and jointed granites,as well as the coal rock dilatancy angle data of different sizes,the applicability of the new dilatancy angle model to the engineering rock mass was explored.2.A non-associated plastic flow rule and an elastic-plastic numerical and semi-analytical method considering the three-dimensional strength and dilatancy characteristics of deep rock mass were established（a）The plastic non-associated flow rule and numerical calculation method considering the dilatancy effect of the deep rock mass.The non-associated flow coefficientβwas introduced into the smooth GZZ criterion,and the plastic non-associated flow rule considering the three-dimensional strength and the dilatancy characteristics of the rock mass was established.The specific mathematical form and value method ofβwere given through theoretical derivation.The correctness and reliability of the non-associated flow rule and the numerical calculation method were verified by the semi-analytical solution of the circular tunnel,the deformation test data of model tests with different buried depths,and the field deformation monitoring data of the deep-buried Grand Canyon tunnel.（b）Three-dimensional elastic-plastic semi-analytical method for deep circular tunnels.Based on the smooth GZZ strength criterion,a new elastic-plastic semi-analytical solution for deep-buried circular tunnels was proposed and verified with numerical solutions.A unified incremental softening equation of out-of-plane（axial）stress was proposed,and the consistent softening law of axial stress in the plastic zone of deep-buried tunnels was revealed.The influence of rock mass quality（GSI）,dilatancy angle,initial test axial stress,as well as theoretical models such as constitutive law（elastic-perfect plasticity,strain-softening and elastic-brittle plastic）and strength criterion（Hoek-Brown criterion and smooth GZZ）on the stability of surrounding rock,were discussed.（c）Numerical simulation and model test of surrounding rock progressive failure of variable stress（burid depth）rock mass tunnel.Based on the existing model test data,two value methods of model rock parameters and corresponding reliability were given.The comparison between the numerical calculation results of surrounding rock deformation and the monitoring datas of model tunnel verified the correctness of the smooth GZZ strength criterion and its numerical calculation method.The progressive failure law of surrounding rock under complex stress conditions and variable buried depth conditions were revealed.The differences of tunnel deformation and failure under the structure and self-weight stress field were summarized.3.A three-dimensional forward analysis method and stress control design analysis method for deep buried rock tunnels based on digital in-situ testing were proposed（a）Three-dimensional continuous analysis and dynamic design method of surrounding rock stability in deep tunnels.A 3D forward analysis and dynamic design method for rock mass engineering based on digital in-situ testing was proposed.The distribution and transfer law of deep surrounding rock stress and deformation were analyzed by taking the deep buried tunnel of Sichuan Grand Canyon as an example.The numerical calculation results obtained by different strength criteria were compared with the in-situ deformation monitoring data to verify the correctness and reliability of the smooth GZZ strength criterion and its numerical calculation method.The mechanical influence mechanism of the intermediate principal stressσ₂ and the three-dimensional stress state on the stability of the surrounding rock and the distortion of the steel arch in the deep tunnel was quantitatively explained.The differences in the analysis results of different analysis models,plane strain and three-dimensional model near the tunnel face,were compared.Finally,it was clarified that the longitudinal stiffness and overall stiffness of the supporting system should be paid attention to in the design and construction of deep tunnels.（b）Three-dimensional spatial effect and stress control design analysis method of the deep-buried tunnel.The three-dimensional finite element numerical simulation of the excavation process of tunnels with different buried depths was carried out.The distribution and evolution characteristics of the plastic zone of the deep-buried tunnels with the excavation,the stress state of the excavation surface and the nonlinear variation law of the extrusion deformation with the buried depth were analyzed.The rotation law of the principal stress axis during the excavation of deep tunnels was revealed,and the quantitative evaluation indicators of the transfer degree were proposed.The complex stress paths near the excavation face of deep tunnels and the time evolution mechanism of nonlinear extrusion deformation.were revealed.Based on the idea of stress control,the stress control mechanism of surrounding rock was studied and the corresponding quantitative stress control approach was given.The important role of advanced core rock mass reinforcement in active control of surrounding rock stability was quantitatively evaluated,and the consistency law of pre-extrusion deformation and pre-convergence deformation of advanced core rock mass was found.Finally,the importance of stress control and active control in the engineering design and control of deep-buried tunnels was discussed.