The Applicability of the Ground Response Curve to Tunnelling Problems that Violate Rotational Symmetry

The applicability limits of the closed-form solution to the problem of ground response to tunnelling are sounded out by systematically investigating the effect of deviations from some of the important assumptions underlying the closed-form solution. The ground response curve (GRC) expresses the relationship between tunnel support pressure and the radial displacement of the tunnel boundary on the basis of a rotationally symmetric model. The assumptions underlying rotational symmetry are a circular tunnel, a hydrostatic and uniform initial stress field, an isotropic and homogeneous ground and uniformly distributed support pressure. Deviations from these assumptions generally necessitate potentially time-consuming numerical analyses. The paper revisits the classical problem of tunnel excavation in a linearly elastic, perfectly plastic ground obeying the Mohr-Coulomb yield criterion, and analyses the effects of non-uniformity and anisotropy of the initial stress field and of a non-circular tunnel geometry. The results show that the GRC also provides a reasonably accurate approximation of average tunnel convergence for a wide range of ground conditions that violate rotational symmetry.