FAILURE DESIGN OF JOINTED ROCK STRUCTURES BY MEANS OF A HOMOGENIZATION APPROACH

Conceived as a potential alternative to the methods usually employed f or evaluating the stability of jointed rock masses, the homogenization approach developed in this paper stems from the intuitive idea that, from a macroscopic point of view, a rock mass intersected by a regular network of joint surfaces may be perceived as a homogeneous continuum . The failure criterion of such an equivalent medium is theoretically determined from the knowledge of the failure conditions of the individ ual constituents, namely the intact rock matrix and joint interfaces. Owing to the existence of privileged material directions associated wi th the joint orientation distribution, this criterion turns out to be of the anisotropic frictional type, as shown by the closed-form expres sion obtained in the particular case of two mutually orthogonal joint sets. This criterion is then applied to the investigation of two illus trative engineering problems: the calculation of the load-bearing capa city of a shallow foundation on a jointed rock half-space and the stab ility analysis of an excavation. Both problems are handled by means of the kinematic method of yield design, making use of the previously de termined macroscopic failure condition. The upper bound estimates thus derived appear to be significantly better than those obtained from a direct analysis in which the intact rock matrix and joints are conside red separately. In spite of some limitations regarding its range of ap plicability, which are underlined throughout the paper, the homogeniza tion approach may constitute an appropriate general framework for the design of densely jointed rock structures. (C) 1998 John Wiley & Sons, Ltd.