Elasto-plastic analysis in conventional tunnelling excavation

Abstract

A new, rigorous approach for calculating the distribution of stresses and displacements around a circular opening excavated in a strain-softening generalised Hoek–Brown rock mass is presented. As most of the current solutions are relevant to elastic-perfectly plastic and elastic-brittle plastic material, it is worth developing a new analytical-numerical approach to address this end. This paper presents an elasto-plastic solution for the axisymmetrical problem of excavating a circular opening in generalised Hoek–Brown material. In the plastic region it is assumed that all the strength parameters are linear functions of the plastic shear strain. By invoking the Runge–Kutta fourth-order method the problem is solved numerically, and states of stress and displacement in the plastic region are determined. The accuracy and practical application of the proposed approach are shown through several examples. For elastic-perfectly plastic and elastic-brittle plastic cases, the proposed approach shows excellent agreement with closed-form solutions. Similarly, for the strain-softening case, this method is in good agreement with current rigorous methods. The influence of the softening parameter, appearing in the evolution of strength parameters, is examined by the construction of different ground reaction curves, and the influence of different definitions for dilation angle in the plastic region is investigated.