As projects advance to deeper levels, rockbursts occur more frequently. The rockburst failure mode is particularly problematic, as the rock mass fails abruptly, releasing large amounts of energy. Laboratory tests and observations in tunnels and mines with high overburden have shown that certain rock types have a high potential for storing elastic energy and are hence more prone to rockbursting. In this research we studied the influence of a rock's heterogeneity at grain scale on its rockburst propensity. Several artificial sample sets consisting of a very fine-grained fibreless ultra-high performance concrete (UHPC) and a constant volumetric fraction of different coarse rock grains as aggregate were produced and tested. The added rock grains were chosen based primarily on their differing stiffness characteristics. One sample set, consisting of pure UHPC, acted as reference for the matrix. The findings of this study confirm that the material's heterogeneity at grain scale has a major impact on the failure behaviour. With increasing stiffness heterogeneity between the ‘rock matrix’ and admixed grains the failure mode becomes more ductile and a lower uniaxial compressive strength is reached. Hence, the material is less prone to rockbursts as less elastic strain energy is developed prior to failure. The results agree well with various rockburst parameters, which were additionally evaluated and compared. The findings allow a better understanding of the underlying mechanism of rockbursts and demonstrate the usefulness of petrographic information in rockburst risk analysis.
Predicting the behaviour of the rock mass is of utmost importance in tunnelling and mining. Only if the potential failure mechanisms of rock and rock mass are well understood can failure be foreseen and avoided and the consequences reduced. Rockbursts are particularly problematic, as the rock mass fails abruptly, rapidly releasing great amounts of energy. Laboratory tests and observations in tunnels and mines with deep overburden have shown that certain rock types have a high potential to store elastic energy. Hence, they are more prone to rockbursting. The amount of stored energy also determines the magnitude of the event.