Ground Response of Circular Tunnel in Poorly Consolidated Rock

To study the surface-closure curve of a circular tunnel in poorly consolidated rocks, closed-form solutions for stresses and displacement near a circular opening subjected to a uniformly distributed external stress and internal pressure are obtained. An elastoplastic model incorporating the nonlinear Hoek-Brown criterion is used, as most poorly consolidated geomaterials display a nonlinear correlation for the strength curve. Because most existing closed-form solutions as such were obtained with a linear Mohr-Coulomb criterion, the proposed solution is compared to those results by the linear criterion to evaluate the possible effect of the linear assumption. It is concluded that the calculated results by the linear Mohr-Coulomb criterion may overestimate the surface closure in low normal stress, but underestimate the opening closure under high normal stress. For the nonlinear case, a comparison is also made between the results by using the associated flow rule for plastic deformation and by a nonassociated flow rule. It is shown, by comparing the calculated results with an experimental result, that a nonassociated flow rule should be used in general. It is suggested that a nonlinear yield criterion be used with a nonassociated flow rule to achieve an appropriate prediction for the opening surface-closure curve.