Abstract

The Q-slope classification system is used to assess the stability of excavated rock slopes and provide an indication of long-term stable, reinforcement-free slope angles. Q-slope is based on over 500 rock slope case studies from mines, road and rail cuts hosted in igneous, sedimentary and metamorphic rocks around the world. Q-slope has successfully been applied to slopes ranging from less than 5 m to more than 250 m in height in both civil and mining environments since its introduction in 2015. This paper describes the application of Q-slope to excavated coal mine slopes which are often hosted in complex, interbedded sedimentary strata. Q-slope application to coal mine slopes is compared to the likelihood of failure calculated by the Slope Stability Assessment Methodology (SSAM). A relationship between Q-slope and SSAM is also provided.

Introduction

Empirical rock mass classification systems and design charts provide geotechnical engineers: (i) a rapid means of predicting of slope behavior; and (ii) guidance on stable slope geometry (e.g. bench face angle, height and width). They are most effective when the geometry, geology, hydrogeology and geomechanical properties of the slope under review are similar to known performance of precedent slopes [1], [2], [3].

The Q-slope classification system [4], [5] and SSAM [6], [7] are two classification systems that have been designed for excavated rock slopes.

This paper describes the application of Q-slope to 38 failed and intact slopes from Australian open cut coal mines. It further describes the relationship between Q-slope and SSAM to predict slope performance.

The Q-slope Classification System

The Q-slope classification system was introduced by Barton and Bar [4] to provide a correlation between Q-slope ratings and long-term stable, reinforcement-free slope angles. Q-slope is an adaption of the Q-System [8] which was initially developed to assess tunnel and rock cavern stability and support requirements. Q-slope is based on over 500 open pit mine bench slopes and road and rail cuts from Asia, Australia, the Americas and Europe, which are hosted in igneous, sedimentary and metamorphic lithologies [5], [9]. Q-slope has also been applied to saprolitic and highly weathered rocks [10] and faulted rocks and fault zones [11].

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