Study On Mechanism Of Collaborative Bearing Effect Of Rock-Support System In Deep Tunnel Construction

With the rapid development of global economy and the gradual expansion of human living space,many underground projects under construction and planning continue to march into the deep rockmass.At present,the underground tunnels for mining mineral resources and traffic construction,underground caverns for water conservancy and hydropower projects and nuclear waste disposal projects at home and abroad have reached a depth of more than 1000 km.With the increase of buried depth,the geomechanical environment of deep rock mass changes greatly compared with that of shallow rock mass.The nonlinear mechanical characteristics of rock mass are more significant,and the stability of surrounding rock is more prominent.Due to the lack of sufficient understanding on the mechanism of collaborative bearing effect between deep rock mass and supporting structures,the engineering analogy method based on empirical design often leads to the supporting structure being too conservative in some cases,causing a lot of waste,and in the other cases too dangerous,resulting in the support failure or even tunnel collapse,which brings great harm to the safety of tunnel construction.Therefore,it is of great theoretical and engineering significance to carry out the research on mechanism of collaborative bearing effect of rock-support system for deep tunnel construction,whether for the optimization of supporting structure design or the stability analysis of surrounding rock.Based on the engineering background of Xianglushan Tunnel of Yunnan Water Diversion Project in China,this paper studies the mechanical characteristics and nonlinear strength criterion of deep surrounding rock under high geostress by means of laboratory test.Then the mechanical model of collaborative bearing effect of rock-support system considering material nonlinearity and contact nonlinearity in deep tunnel construction is established.Next,the numerical analytical method of collaborative bearing effect of rock-support system based on elastoplastic contact iteration is established.Finally,the true three-dimensional geomechanical model test on Xianglushan tunnel construction is carried out,which reveals the mechanism of collaborative bearing effect of rock-support system,and verifies the reliability of the mechanical model of collaborative bearing effect of rock-supporting structures.The main results obtained by the paper are as follows:(1)The laboratory physical and mechanical tests of 1000 meter deep limestone and silty mudstone from Xianglushan tunnel are carried out,and the nonlinear mechanical characteristics,failure modes and mechanical parameters of deep soft rock and hard rock under different stress conditions are obtained.Based on the Hoek-Brown criterion,a nonlinear strength model considering the post-peak softening characteristics of surrounding rock is proposed,and the corresponding UMAT program is developed based on ABAQUS platform.(2)The mechanical test of the rock-concrete interface under different roughness conditions was carried out.Based on the fractal geometry theory,a nonlinear contact model of the surrounding rock-lining interface was proposed.Combined with the nonlinear strength model of deep surrounding rock,the mechanical model of collaborative bearing effect of rock-supporting structures considering material nonlinearity and contact nonlinearity in deep tunnel construction is established.In view of the difficulty that there is no closed analytical solution to the problem of rock-support interaction,the iterative calculation method of "incremental support load method" is proposed,and the corresponding solution program is developed by MATLAB.(3)The numerical calculation method for collaborative bearing effect of rock-support system based on elastoplastic contact iteration is established,and the corresponding calculation program is developed based on ABAQUS platform.Through numerical calculation of construction process of Xianglushan Tunnel,the influence law and sensitivity ranking of rock-lining interface roughness,tunnel depth and support time and other factors on the cooperative bearing effect of rock-support system are obtained.(4)The true three-dimensional geomechanical model test of Xianglushan Tunnel is carried out.The complex geological conditions and dynamic construction process of the construction site are truly reproduced.The variation laws of stress and displacement in surrounding rock,contact pressure between surrounding rock and lining,and bolt axial stress are obtained.The collaborative bearing effect of rock-support system during deep tunnel construction is revealed.The reliability of the mechanical model and corresponding numerical method of the collaborative bearing effect of rock-support system is proved,which provides scientific guidance for the construction of deep tunnel and the design optimization of supporting structure...