Stability of underground excavations is of utmost concern in both mining and civil engineering projects. The brittle Hoek-Brown parameters (m = 0 and s = 0.11) introduced by Martin et al. (1999) were found to be very useful in assessing the stability conditions of underground excavations. However, observations in granodiorite at the Underground Research Laboratory (URL), in quartzite at Thompson Mine, and in stopes in sulphide ore bodies reveal that the use of the current brittle Hoek-Brown parameters over-predicts the depth of failure in some rock types. These observations lead to a conclusion that the brittle Hoek-Brown cohesive parameter s is not constant at 0.11 for all rocks but varies depending on rock type.; The objectives of this thesis are to identify the factors that cause brittleness in rocks and to develop a brittle rock rating system for selected rocks, such that the rating system can be used to get the appropriate brittle Hoek-Brown parameter s for different rock types.; A numerical code, RFPA2D (Tang, 1997) was used to quantitatively determine the effect of material heterogeneity on brittleness of rocks. A flowchart and procedure are developed to rate the brittleness of selected rocks based on grain size, mineralogy and foliation conditions. (Abstract shortened by UMI.)
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