The longitudinal loading mode evaluation of fault-crossing tunnel by a new load equivalence method based on a Pasternak model

The deformation and failure of fault-crossing tunnel attributes to its weak mechanical behavior near the fault core under a certain longitudinal loading mode when a tunnel is passively subjected to a normal faulting. A reasonable analytical solution to deal with the complex dislocation issues for fault-crossing tunnel by an elastic beam model is convenient to reveal the dislocation response of tunnel. In view of this, the longitudinal loading mode of tunnel was discussed by a new load equivalence method based on a hypothetically longitudinal deformation pattern of tunnel along the transition zone. Subsequently, a numerical model was built to reveal the mechanism response of tunnel emerged in the strata containing a fault core to verify the correctness of the proposed analytical evaluation method. And then, the proposed load equivalence method was applied to the scenarios involving fault fracture zone and its adaptability was confirmed numerically and experimentally. The results showed that the presumptive loading mode under the proposed load equivalence method of tunnel was available relying on the deformation and force indices. Under the deformation profile mode at transition zone, the maximum bending moment appears at the ends of the deformed profiles, and the sections near fault core present the negative shear behavior. The analytical prediction at loading mode can be widely applied at the fault-crossing tunnel emerged in the field with fault fracture zone, and the length of the transition zone of tunnel is about 1.2 times of the width of fault fracture zone appropriately.