Stress and displacement of surrounding rock of loess tunnels based on joint strength

The stress and displacement of surrounding rock of tunnels are one of the traditional research subjects in the tunnel engineering. However the impact of tensile strength on stress and displacement of the surrounding rock of structured loess tunnels needs to be evaluated reasonably. Based on the theory of joint strength considering the tensile and shear properties of loess simultaneously, the principal stress expression for the strength failure curve is re-determined to analyze the ultimate stress equilibrium. Then, the radius of the plastic zone of the surrounding rock of loess under the axisymmetric circular tunnel is re-determined. Finally, the expression of the displacement for the surrounding rock around the tunnel is obtained. The results show that the plastic stress in the surrounding rock determined by the joint strength theory is smaller than that determined by the traditional Mohr-Coulomb theory, and the radius of the plastic zone and the displacement of the surrounding rock around the tunnel are relatively large. The joint strength theory based on tensile strength overcomes the defect of Mohr-Coulomb theory overestimating the tensile strength of loess, and it can reasonably evaluate stress and displacement of the surrounding rock.