Damage Mechanics Analysis of Underground Opening in Jointed Rock Mass

Mechanical effects of discontinuity are of paramount importance in estimating deformation and collapse behaviour of geotechnical structures in discontinuous rock mass. Although several numerical methods have been proposed to treat distinct discontinuities of relatively large scale such as fault, there is no powerful method which can take into account the effect of distributed discontinuities of small scale. Kyoya et al. ¹⁾²⁾ proposed a damage mechanics theory for discontinuous rock mass which treats the behaviour of rock mass involving distributed discontinuities. In the theory, the effect of distributed discontinuities is characterized by a second order symmetric tensor, called the damage tensor, which is originally proposed by Murakami and Ohno³⁾⁴⁾ in their creep damage theory for metallic materials. In this paper, the damage mechanics theory is applied to an underground opening problem in jointed rock mass, and then the numerical results by finite elements are compared with a conventional finite element analysis. It is shown that the damage model presents presumably reasonable results for deformation and failure zone around the cavern. That is, the damage analysis can estimate the anisotropic behaviour of rock mass caused by the distributed discontinuities.