| With the continuous advancement of Transportation Power and Maritime Power Strategy,more and more underground engineering is constructed within the water-rich jointed rock mass.Under this engineering environment,due to the long-term coupling effect of stress field and seepage field,the cracks in the surrounding rock of the caverns are easy to initiate,propagate and coalesce,resulting in the failure and instability of the surrounding rocks,seriously threatening the safety and long-term stability of the underground structures,and even causing severe engineering disasters.Therefore,it is necessary to clarify the time-dependent propagation and evolution characteristics of cracks in rock mass under hydraulic coupling,systematically study the time-related behaviors of crack initiation,propagation,and coalescence,grasp the influence of crack propagation and interaction on the macro-mechanical performance of surrounding rock,for controlling the occurrence of engineering disasters,and ensuring the safety of underground structures in construction and operation.However,there is still a lack of systematic understanding of the spatial propagation of cracks and the fracture mechanism of rock mass in complex environments.The time-dependent propagation of cracks and mechanical behaviors of rock mass are not clear.There is no creep mechanical model of rock mass which can comprehensively reflect the coupling effect,crack propagation evolution and interaction behavior.In addition,the accuracy of longterm stability analysis method based on the traditional creep model is poor,which is difficult to provide scientific evidence for engineering practices.In response to the problems mentioned above,we comprehensively adopt the main research methods such as laboratory test,theoretical analysis,and numerical simulation to investigate the fracture evolution mode and main influencing factors of the 3D jointed rock mass.A model of subcritical crack propagation and rock mass creep failure under hydromechanical coupling is established.A fracture-seepage-creep coupling model for rock mass and corresponding long-term performance prediction method are proposed.Applied research is carried out on the surrounding rock of typical tunnel engineering,to provide a theoretical basis for the safety and long-term stability assessment of underground engineering construction.The main research work and results of this paper are summarized as follows:(1)It is easy for the cracks in rock masses to initiate,propagate,and coalesce under the combination of high ground stress and seepage pressure,which leads to the failure of rock masses.In order to investigate the initiation and propagation modes of 3D crack under hydro-mechanical coupling,a numerical model was established by the 3D fracture analysis code of FRANC3D.The numerical simulation and the corresponding laboratory failure experiments based on the transparent resin rock-like material were carried out.Based on the contribution rate of three basic fracture modes,the criterion of energy release rate was modified and the parameters were optimized.The applicability of different fracture criteria was analyzed by comparing it with laboratory results,and then the reliability of the model was validated.Based on the numerical simulation,the distribution characteristics of fracture parameters along the crack fronts under different loading conditions were analyzed.The influences of key factors such as water pressure and lateral stress on the angles and lengths of 3D crack propagation were obtained,and the failure mechanism of jointed rock masses was revealed,which laid a foundation for the study of time-dependent characteristics of rock failure under hydromechanical coupling.(2)Crack propagation and rock failure under hydromechanical coupling have typical time-dependent characteristics,and subcritical crack propagation is one of the most important causes of rock instability.Rheological tests based on mortar specimens containing single internal 3D cracks and the corresponding numerical simulations are carried out to investigate the time-dependent characteristics of the crack propagation and the failure mode of rocks.The crack propagation-interaction behaviors and the specimen rheological failure mode were investigated based on the test results;The evolution characteristics of the cracks and pores were further analyzed based on the low-frequency nuclear magnetic resonance technology.The finite element fracture analysis software was used to establish a time-dependent crack propagation model,and the numerical simulations were carried out to investigate the propagation and interaction of crack.besides,the effects of water pressure,crack dip angle,crack shape,crack spacing and bridge angle were analyzed.(3)Under the long-term coupling effect of groundstress and underground water pressure,the subcritical propagation and interaction of cracks are important factors affecting the creep deformation and progressive fracture behavior of rocks.In order to study the creep mechanical properties and time-dependent failure modes of rocks containing 3D cracks,long-term hydromechanical coupling triaxial creep tests and conventional triaxial compression tests were carried out based on rock-like specimens with pre-fabricated 3D cracks.The subcritical propagation characteristics of cracks and creep deformation modes of specimens were compared and analyzed.A theoretical creep model of jointed rock mass was proposed by introducing water pressure and boundary effect.Based on the subcritical propagation and interaction of cracks,the creep rate model of rocks was established.In terms of the test data,the interaction parameters of cracks were analyzed,the mechanism of rock creep and the influence of water pressure were revealed,and the time-dependent characteristics of propagation and interaction of cracks and its influence mechanism on rock deformation were clarified.(4)When the underground engineering passes through the water-rich jointed rock mass,the modes of crack propagation,coalescence and interaction are more complex.The jointed rock mass presents obvious progressive damage characteristics,which seriously threatens the long-term performance of the surrounding rocks of the engineering.Therefore,based on the time-dependent characteristics of crack propagation evolution and interaction mechanism,the fracture damage characteristics,seepage coupling characteristics and rheological characteristics of jointed rock mass were studied,and a theoretical calculation model of fracture-seepage-creep coupling for rocks was proposed.The theoretical models,including fracture damage module,seepage coupling module and time effect module,were compiled by computer language and embedded into the extended finite element analysis model.Based on the above theoretical models and methods,the long-term stability analysis of surrounding rocks was carried out for a typical tunnel project with long-term coupling effect of seepage pressure and groundstress.The service life and state of the surrounding rocks were predicted.The influence mechanisms of tunnel buried depth,seepage water pressure and distribution of jointed weak zone were clarified.The research results can provide certain theoretical guidance and scientific evidence for the evaluation of long-term safety service state of similar projects. |
PDF Full Text Request