Abstract
Weak rocks can be found in many mines around the world with strengths varying from extremely weak (R0) to very weak (R1) and to weak (R2). R0 materials are usually treated as soils, whereas materials from the middle to upper R2 strength range can be assumed to behave as a rock mass. The problem is therefore the handling of so-called R1 to R2 materials.
Based primarily on experience in weathered rocks in Brazil, an adaptative approach is herein proposed to provide a quick field estimation of rock strength based on subdivisions R1−, R1+, R2− and R2+, which are used to estimate the likely rock mass strength and behaviour.
This chapter proposes adjustments to Rock Mass Rating (RMR)—Bieniawski classification for weak rock masses focusing on a connection to strength rather than a behavioural (stable–not stable) approach.
A low-end transition Hoek–Brown relationship is proposed to represent the strength of weak rock masses, which bridges the gap between a more matrix-controlled rock mass behaviour (R1−) and inter-block shear failure (R2+). Strength parameters estimated with this low-end transition function are compared to bearing plate load test results and to back-analysis results of a mine slope excavated in altered rocks.
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Cella, P., Castro, L., Carter, T. (2020). Mining Slopes in Weathered and Weak Rocks. In: Kanji, M., He, M., Ribeiro e Sousa, L. (eds) Soft Rock Mechanics and Engineering . Springer, Cham. https://doi.org/10.1007/978-3-030-29477-9_13
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