Coupling analysis of longitudinal deformation profile and ground reaction curve

At present, most of the existing studies on the spatial excavation effects are conducted by means of the elastic and elastic-perfectly-plastic models. However, the rock masses with different ranges of geological strength index (GSI) exhibit different behaviors during post-peak stages. An appropriate mechanical model should be adopted to study the longitudinal deformation profile (LDP). Then, LDP can be coupled to ground reaction curve (GRC) so as to aid the support design. By use of the finite difference method, a simple analysis approach is proposed. Based on the Hoek-Brown and Mohr-Column failure criteria, this method can obtain LDPs and GRCs using elastic-perfectly-plastic, elastic-brittle-plastic and plastic strain-softening models. The calculated results are compared with those from other existing methods to verify the calculation accuracy of the proposed method, and a further study is made to investigate the virtual support pressure at a certain location behind the excavation face. The results indicate that the higher the value of GSI, the greater the difference of virtual support pressure for the three models, and thus it is more necessary to consider the post-peak mechanical behavior of higher value of GSI realistically; for an intermediate and relatively high value of GSI, an elastic-perfectly-plastic model leads to a conservative estimation of the support design as the distance to the excavation face is within approximately 0.8 of the tunnel radius, and the case is quite contrary while the distance is over 0.8 of the tunnel radius.