Study On Unloading Effect And Deformation Failure Mechanism Of Jointed Surrounding Rock In High Temperature And High Pressure Tunnels

With the in-depth implementation of the construction of ’ transportation power ’,the construction of transportation infrastructure has developed rapidly.The number and mileage of tunnels in China have also increased rapidly and gradually developed in the direction of ’ deep,long and large ’.With the increase of buried depth,the problems of high temperature and pressure encountered during tunnel excavation are becoming increasingly prominent.The loading and unloading mechanical properties of rock mass at high temperatures are different from those at normal temperatures.The stress adjustment and deformation and failure mechanism of tunnel surrounding rock under high temperature and pressure are also more complex than shallow engineering.Therefore,in view of the characteristics of high temperature and high pressure in deep buried tunnels and the characteristics of the development of joint fissures in rock masses in southwest China,it has become a practical need to carry out research on the mechanical characteristics of loading and unloading of jointed rock masses under high temperature and high pressure,as well as research on the evolution of temperature and stress fields in jointed surrounding rock during tunnel excavation,as well as the mechanism of disaster occurrence.In this thesis,theoretical derivation,experimental investigation and numerical simulation are combined.The unloading effect and deformation failure mechanism of jointed surrounding rock of deep buried high temperature and high pressure tunnel are studied as the main line.The loading and unloading mechanical properties of high temperature and high pressure jointed rock mass,the multi-field evolution and disaster mechanism of surrounding rock in high temperature and high pressure tunnel excavation,and the stability judgment of surrounding rock in deep tunnel excavation were studied.The main research results are as follows :(1)The evolution and distribution characteristics of temperature and stress fields in surrounding rock of high temperature and high pressure tunnel excavation are clarified through theoretical derivation.The theoretical solution of the temperature field of surrounding rock in tunnel excavation is solved by combining Laplace transform and Bessel equation.At the same time,the complex variable function method is used to solve the temperature stress and the total stress of the surrounding rock during the cooling process.The evolution law of temperature field and stress field of surrounding rock is clarified.Finally,based on the theory of fracture mechanics,the expression of stress intensity factor at the joint end of rock mass with temperature is derived.(2)The mechanical properties,crack development laws,failure modes,and energy evolution laws of jointed rock masses under uniaxial compression at normal and high temperatures are revealed.Uniaxial compression tests of intact and jointed rock masses were conducted at room and high temperatures.The mechanical properties of single filling and cross filling jointed rock masses under different temperature states are clarified.The variation laws of mechanical properties of different jointed rock masses are explained from the perspective of mesoscopic numerical models.The development rules and failure characteristics of failure cracks in different jointed rock masses are revealed.The failure cracks are divided into five categories.The energy index characteristics of each jointed rock mass during compression are analyzed based on the energy principle.The energy evolution law of jointed rock mass during compression is revealed,and the evolution process is divided into four stages.(3)The damage evolution model and damage constitutive model of high temperature jointed rock mass are constructed.Based on the principle of damage mechanics,considering the coupling effect of temperature and load,the damage evolution equation of high temperature jointed rock mass under load is derived.Based on the damage evolution equation,a damage constitutive model of jointed rock mass considering initial damage and high temperature thermal damage is established.The correctness of the model is verified based on the experimental results.(4)The calculation model of loading and unloading strength of intact rock and jointed rock mass under different temperatures is established.Triaxial tests of intact rock and jointed rock under axial compression and unloading confining pressure at room temperature and high temperature were carried out.The loading and unloading mechanical properties of different jointed rock masses at room temperature and high temperature are clarified.The loading and unloading failure modes and crack development characteristics of each jointed rock mass are revealed.The Boltzmann model was used to fit the variation of loading and unloading strength of intact rock,single joint and cross joint rock mass with temperature.Based on the parameter characteristics of the triaxial loading and unloading strength change model of the three types of specimens,a unified calculation model of the loading and unloading strength of intact rock and jointed rock mass with temperature change is obtained.Based on the experimental results,the rationality of the model is verified,and the absolute error between the experimental value and the calculated value is within 5 %.(5)The multi-field evolution law of surrounding rock and the deformation and failure evolution mechanism of jointed surrounding rock under high temperature and high pressure are clarified.Considering the heat conduction process of surrounding rock after tunnel excavation,the variation law of temperature,stress and displacement field of surrounding rock after tunnel excavation under different temperature fields and different initial stress fields is clarified by numerical simulation.The excavation deformation failure law and surrounding rock disaster mechanism of layered jointed surrounding rock with different dip angles and cross jointed surrounding rock with different angles are revealed.The evolution process of deformation and failure can be divided into two major stages.(6)A ’deduction-inversion-superposition ’inversion method of ground stress field of deep buried tunnel considering the influence of high ground temperature is proposed.Based on the detailed investigation of the project,a complex three-dimensional refined geological model is established.Based on the characteristics of regional ground temperature distribution,a ’deduction-inversion-superposition ’inversion method of ground stress field considering the influence of high ground temperature is proposed.The comparison verifies the rationality and necessity of considering the influence of high ground temperature in the inversion of deep buried engineering ground stress field.The inversion error of more than 80% of numerical points in the inversion results using this method is less than 10%.Finally,the stability of surrounding rock in tunnel excavation is judged from the perspective of temperature,stress and displacement evolution of surrounding rock after excavation in high temperature and high pressure section.