Study On The Zonal Fracture Characteristics Of Deep Surrounding Rock Under The Coupling Of High Ground Stress And High Ground Temperature

Under high ground stress conditions,deeply buried tunnels are susceptible to zonal rupture after excavation,which is compounded by the effects of high ground temperature.Therefore,it is necessary to study the mechanism of zonal rupture of surrounding rocks under the coupling effect of high ground stress and high ground temperature.In this thesis,based on the Jijinshan tunnel along the Sichuan-Tibet route,the rupture mechanism of the deep surrounding rocks under the coupling of high ground stress and high ground temperature is studied by combining theoretical calculation analysis and threedimensional numerical simulation,and the main findings are as follows:(1)The geological and mechanical characteristics of the deep rock mass under the coupling effect of multiple fields are investigated.The mechanical characteristics are mainly manifested in the complexity of the surrounding rock stress field,large deformation of the surrounding rock,strong rheological characteristics and brittle-ductile transformation characteristics;meanwhile,by summarising the zonal rupture phenomenon observed in the field so far,the root cause of the zonal rupture phenomenon is qualitatively analysed.(2)By analysing the temperature field of the surrounding rock,the temperature stress expression is obtained;on this basis,based on the double shear unified strength theory and combined with the differential equilibrium equation,the elastic-plastic stress of the surrounding rock is analysed,and the theoretical formulae for calculating the radius of the plastic zone and the radius of the loosening circle of the surrounding rock under the action of heat-force coupling are proposed;and the effects of the initial ground stress,ground temperature difference,intermediate principal stress and the radius of tunnel excavation on the radius of the plastic zone are analysed,so as to study the The influence of initial ground stress,ground temperature difference,intermediate principal stress and tunnel excavation radius on the radius of the plastic zone is analysed,thus investigating the parameters of the plastic zone.The results show that:(i)the radius of the loosening circle increases with the increase of the initial ground stress and the ground temperature difference,with the initial ground stress playing a major role in the radius of the loosening circle and showing a non-linear relationship;(ii)the radius of the loosening circle increases approximately linearly with the increase of the tunnel excavation radius,and decreases with the increase of the intermediate principal stress coefficient,and the smaller the intermediate principal stress coefficient,the more sensitive the stability of the surrounding rock to the intermediate principal stress.The smaller the intermediate principal stress coefficient,the more sensitive the stability of the surrounding rock is to the intermediate principal stress.(3)The applicability of the double-shear unified strength theory to deep rock masses is analysed by summarising the commonly used damage criteria for existing rock masses;at the same time,the effect of high ground temperature on the thermodynamic parameters and initial ground stress of rock masses is investigated to analyse the temperature effect on the zonal rupture of surrounding rocks;on this basis,the stress field in the rupture zone of surrounding rocks is analysed based on the double-shear unified strength theory,and theoretical formulae for the radius of the rupture zone and the distance between adjacent rupture zones are proposed,and then the mechanical mechanism of the zonal rupture of surrounding rocks is analysed.(4)Based on the G351 Line Jijinshan Tunnel Project,a three-dimensional numerical model was established and coupled thermal-force analysis was carried out using the finite-difference calculation software FLAC 3D.The effects of thermodynamic parameters such as burial depth,lateral pressure coefficient,linear expansion coefficient,ground temperature,cohesion and internal friction angle on the rupture of the surrounding rock were analysed.The results show that with the increase of burial depth,lateral pressure coefficient,linear expansion coefficient and ground temperature,or the decrease of cohesion and internal friction angle,the number of plastic zone strips increases and the length becomes longer,and the zonal rupture tends to be more serious;among them,the linear expansion coefficient has the greatest influence on the zonal rupture of deep surrounding rocks.