Viscoelastic Plastic Deformation Of Tunnel Surrounding Rock And Analysis Of Stratigraphic Settlement

Due to the needs of daily production and life,more and more projects involve the excavation of tunnels.In recent years,the accidents related to tunnel are common so it is necessary to study the deformation of tunnel rock mass.Because the deformation of rock mass is the result of multi factors,the study of the influence of various factors on the deformation of the surrounding rock and the settlement of the ground surface is beneficial to effectively control the deformation of the surrounding rock and the surface subsidence.In this paper,the surrounding rock deformation and surface settlement caused by tunnel excavation is analyzed theoretically.Based on the Levy-Mises constitutive relation and the D-P yield criterion are used.Selecte the Nishihara model,calculate visco elastic plastic deformation of surrounding rock,discuss the deformation law of surrounding rock with Hoek elastic modulus formula;Analyse the deformation and supporting effect of surrounding rock under the condition of variable support with convergence constraint method;Considering the rheological properties of rock mass,obtain viscoelastic complex function solutions of shallow buried tunnel and analyse surrounding rock deformation and surface settlement of shallow buried tunnel;Based on stochastic medium theory,propose the convergence radius of shallow tunnel calculated by the reduction factor and conduct a prediction for the surface subsidence.The main results are as follows:(1)The structural characteristics of rock mass and excavation disturbance have great influence on the deformation of surrounding rock.The better the rock mass is,the smaller the excavation disturbance is,the smaller the deformation of surrounding rock is;When the excavation speed is faster,the deformation of tunnel surrounding rock is more severe;The excavation velocity has little effect on the final deformation of surrounding rock.(2)Support can restrain the deformation of surrounding rock and tunnel excavation should be supported as early as possible;increase the support stiffness at low stress as far as possible while increase the maximum support reaction at high stress as far as possible.(3)The restraining effect of supporting structure on tunnel deformation is limited and in order to achieve better supporting effect large enough supporting force must be exerted.When the lateral pressure coefficient is greater than 1,the surface forms a wide and shallow formation deformation;when the lateral pressure coefficient is less than 1,the surface becomes narrow and deep.(4)Applicable convergence radius of the shallow tunnel obtained by reducing the displacement of tunnel surrounding rock can be used to predict the subsidence well.The research results above have certain reference value for the analysis of rock mass deformation and the stratum subsidence caused by tunnel excavation.