Study On Post-peak Deformation Mechanism And Stability Analysis Method Of Deep Fractured Rock Mass

With the rapid development of China's economy,the demand for underground projects is increasing,but the construction conditions of underground projects are becoming more and more difficult.The buried depth and more intense tectonic activity,the in-situ stress level is the higher;The possibilities and frequency are much higher that these projects happen deep engineering disasters such as continuous large deformation and large volume landslides under the action of the strong excavation unloading,and causing casualties,machinery and equipment obsolescence,part of the tunnel was forced to stop or relocate,serious environmental damage and huge economic losses.These disasters have seriously restricted the our country such as traffic,water conservancy and hydropower project construction and operation safety.T The analysis and study on the process of deformation,failure and instability of deep fractured rock mass is of great practical engineering and social significance for the safety construction of underground engineering.Rock can be assumed to be a kind of inhomogeneous multiphase composite structure;After the external force,the micro-defects randomly distributed in the rock inside are constantly changing,appear through,cracks in the rock gradually formed macroscopic damage,Leading to instability of the rock structure.Rock post-peak stress is very complex and generally is in unstable state,its mechanical behavior is hard to be described with classical strength theory,and the brittle failure is assumed to be continuous media is there is a problem,is not correct.In this paper,Based on the result of indoor triaxial test,the failure and structural instability process of fractured rock are analyzed.In this paper,the main research contents include:1)Uniaxial and triaxial compression tests were carried out on rock-like specimens with pre-fabricated different inclination through cracks.The deformation and fracture process of post-peak fractured rock mass was studied,and the total stress-strain curves of fractured rock mass were obtained.The effects of different inclination and confining pressure on the stress-strain curves,failure modes,peak strength,residual strength and deformation characteristics of fractured rock mass were analyzed.2)According to the principle of similarity test,rock-like and fracture-like materials are made,and large-scale three-dimensional model tests are carried out for excavation deformation and failure law of deep multi-group fracture rock mass.The evolution process of surrounding rock deformation and failure of deep multi-group fracture rock mass with a certain dip angle under excavation and strong unloading is studied.The deformation and fracture process of post-peak fissured rock mass is studied from a macroscopic point of view.The experimental results provide a basis for the study of theory and numerical methods.3)According to the variation characteristics of stress-strain curves obtained from laboratory tests and based on Weibull distribution model,the non-linear continuous damage constitutive relationship of post-peak fractured rock mass is established,and the relationship between parameters of damage constitutive model and confining pressure and joint inclination is discussed.The criterion of rock damage and failure based on strain energy density theory is established,and a new extended distinct element method based on strain energy density theory is proposed.The FISH language in UDEC is used to develop a program for calculating the damage,deformation and fracture process of rocks based on SED-EDEM,which provides numerical conditions for simulating the discontinuous failure process.4)According to the failure and fragmentation pattern of fractured rock mass after excavation by large scale model test,the block group method of Monte Carlo model is proposed to realize the stability analysis of excavated fractured rock mass,and the dynamic visualization calculation program of rock mass stability analysis based on block group method is developed to realize the vector calculation of key blocks,block group generation,geometric analysis and reliability analysis of Monte Carlo model.The functions of dynamic visualization display provide technical support for the study of stability and support design of fractured rock mass.5)On the basis of the above experiments and theoretical studies,and taking the practical engineering as the background,the extended discrete element method based on strain energy density theory(SED-EDEM)is proposed to establish a three-dimensional numerical model.The whole process of deformation and failure of deep multi-fractured rock mass during excavation is analyzed,and the results of large-scale model test are compared and analyzed.In this paper,the research content provides a new method for researching the deformation and failure process of rock mass and the underground tunnel surrounding rock supporting problem,and it has guiding significance for understanding all kinds of massive landslides,large deformation and their supporting role.