This paper illustrates a methodology used to investigate the stability of raises in fractured rock masses. A worked example is utilized to demonstrate how a rock mass can be represented by a fracture system and the resulting system subsequently linked to a numerical stress analysis model. This paper discusses the advantages and limitations of this approach and how it will eventually lead to a design tool that can take into consideration both structure and stress. This paper is part of on-going work on the design of raise systems in underground mines.
The design of underground excavations in rock must account for the influence of structure, stress, as well as the size, shape of an excavation and its intended use. Although there are several analytical, empirical and numerical tools available, it is recognized that these tools have inherent advantages and limitations. The design of mining infrastructure such as ramps, shafts, ore and waste pass systems, and ventilation raises, although critical has not received the same level of attention as the design of drifts and stopes. Furthermore, although infrastructure excavations are often grouped together there are important differences in the underlying design philosophy. The design of the main mine shaft, for example, can be conservative given the important economic and operational ramifications of failure. On the other extreme, there are cases where ore pass raises have been treated as expendable structures that are expected to fail after some time in operation. The stability of ore pass systems, like other excavations, is influenced by the resulting stresses and prevalent structural regimes. They are also expected to maintain their structural integrity, even when subject to impact loads, or wall wear as a result of material being transferred though. Ore pass problems in Canadian mines have been documented by Hadji-georgiou et al. (2005).