Rock mass property determination is one of the most challenging and troublesome quests for the geotechnical community. An accurate and reliable determination of rock mass property becomes increasingly important in ground stability assessment for the mining industry. At present, rock mass classification method such as Geological Strength Index (GSI) is still the dominant method for rock mass property determination. Although such methods have been widely implemented in hard rock sector, questions arise for coal measure rock applications. Most rock mass classification methods haven't fully accounted unique geological characteristics of coal measure rocks and databases of many classification methods contain disproportionate hard rock cases comparing to soft rock cases. This paper intends to verify the applicability of some popular rock mass classification systems including GSI, GSI transition function for weak rock, and Dinc ‘s system that have potential to be extended to coal measure rocks. By comparing the predicted and back analyzed rock mass properties of three well documented slope failure cases from Bowen and Hunter coalfield, Australia, the robustness and the applicability of rock mass downgrading systems for coal measure rocks are validated. The results indicate that weak rock mass tends to acquire some soil alike behaviors as the strength decrease but fracture network is the most influential factor of rock mass quality. The results also demonstrate that GSI system can be applied to coal measure rocks although its reliability can be improved by considering the intact rock strength.

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