Accounting for the effect of rock mass anisotropy in stress measurements.

Safety and efficiency of mining operations depend on the quality of design of mining excavations and sequence. A crucial ingredient in mining design is the adequate information of both the original in situ stress and the stress disturbance caused by mining. The main method of stress determination - the overcoring - has a number of drawbacks. 1. It requires an open access to the location of the measurements, which is especially difficult if the stress is to be measured ahead of deep underground excavation. 2. It presumes the rock to be isotropic, while in many cases the rock anisotropy is significant. Subsequently, the isotropic stress reconstruction procedure of the overcoring method can give erroneous stress magnitudes and directions (e.g., Amadei and Goodman, 1982). The rock memory methods - DRA and the Kaiser effect are free from the influence of anisotropy. Moreover the DRA technique can, in principle, provide as a by-product a sufficient number of measurements to reconstruct the full anisotropic tensor of moduli, or compliances sufficient to characterise rock anisotropy, introduce corrections to the overcoring stress reconstruction procedure and quantify the effect of rock anisotropy on the stress concentrations induced by the excavation. In this paper, we present the procedure for the anisotropy characterisation based on DRA and analyse the sensitivity of the procedure and the effects of the rock anisotropy on stress measurements.