A study of the mechanism and regularity of failures in the surrounding rock of a deep buried bias tunnel embedded in geologically bedding strata: taking one tunnel of the Zhengwan line as an example

Deep buried tunnels embedded in geologically bedding thin to medium thick strata often have the bias problem of geological bedding, which leads to partial collapse, bias deformation and support structure damage of tunnels. This paper takes one tunnel of the Zhengwan line as an example and examines the mechanism and regularity of failure in tunnels embedded in geologically bedding strata by using the methods of theoretical analysis and numerical simulation. The result show that (1) the surrounding rocks of the deep buried tunnel embedded in geologically bedding strata will undergo tensile fracture of rocks, shear failure of structural plane and failure of rock mass according to the angle between the tangential stress and structural plane. The tangential stress is parallel to the structural plane, and the tensile fracture of rocks mainly occurs. A the plastic zone of surrounding rock here is the widest, the displacement of surrounding rock here is the largest, and the surrounding rock is in an extremely unstable state. (2) The failure regularity of the tunnels embedded in geologically bedding strata is directly related to the strength parameters of the structural plane, the range of plastic zone and displacement of the surrounding rock decreases with the increasing friction angle of the structural plane, and the decreasing trend slows down gradually. When the friction angle of the structural plane exceeds the friction angle of rock mass, the continuous increase in the friction angle of the structural plane has little effect on the stability of the surrounding rock. (3) The bias distribution characteristics of the plastic zone and the displacement of the surrounding rock rotates wholly with the change in the dip angle of the structural plane, and for the bottom of the tunnel, the most unfavorable inclination of the structural plane is 0°, the maximum heave of the tunnel bottom is greater than that under other dip angles; for the tunnel arch, the most unfavorable inclination of the structural plane is 40°, the maximum convergence value around the tunnel is greater than that under other dip angles, and the most unfavorable position is at the inverted arch waist.