The angle for setting foot reinforcement bolt based on the failure mode of shallow tunnel in loess

Abstract During the construction of shallow tunnel in loess, installation angle of foot reinforcement bolt (FRB) has a significant effect on settlement at tunnel vault. In this paper, according to the failure modes of shallow tunnel in loess, considering the internal force transmission, deformation coordination, and arch foot displacement between the steel frame and the FRB, a mechanical calculation model for joint load-bearing and displacement of the steel frame for primary support and the FRB is proposed, and found that the maximum anti-sliding force is at angle of 47 degrees of FRBs. The calculated angle is used at different sections of the Jianzicha No. 2 tunnel, measured settlement and deformation of the tunnel vault in field tests showed the angle is applicable in construction. By using the finite element simulation, the influence of anchor pipe angle on the settlement of tunnel vault was studied. The results showed that, FRBs at 47 have the best effect in controlling settlement.