Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks

摘要

One common aspect of deep mining is the massive rock mass conditions leading to a failure process where new fractures are created through the rock. Therefore, the three dominate rock mass characteristics required for deep mining deposits are the strength, elastic properties, and pre-mining stress state. This paper focuses on characterising the strength parameters and elastic properties of rocks for deep mining purposes. Too often, strength testing data does not receive proper attention. Details are provided on the specification of confining pressures for both low (excavation skin) and high (squat pillars) confinement design specific challenges, the filtering of data to assess Hoek-Brown intact rock strength envelopes, and the interpretation of testing results. Laboratory testing data from a deep mining deposit is presented to show appropriate filtering for the determination of strength by failure type. Next the importance of understanding the elastic properties is discussed and it is shown how different relative magnitudes in elastic moduli and lithologic unit geometry impact stress and strain changes between rock units. This understanding assists engineers in determining the modulus differences leading to potential stress but, more importantly, strain gradients in the rock mass that have the potential for the generation ofseismicity and rockbursts.