Open Cut » General
This report combined different approaches to investigate the estimation of coal measures rock mass strength from laboratory properties, and in particular their use in the evaluation of open cut coal mine excavated slopes. The report is presented in two parts:
- Report A: Guidelines for Estimating Coal Measure Rock Mass Strength from Laboratory Properties- Empirical Approach; and
- Report B: Guidelines for Estimating Coal Measure Rock Mass Strength from Laboratory Properties- Synthetic Rock Mass Models.
Report A develops approaches including GSIw that improve the estimation of strength of coal measure rock masses from laboratory properties and the analysis of failed slopes. It focuses on weak rocks, i.e. those commonly with a uniaxial compressive strength of less than 20 MPa, which are not well accounted for in many geotechnical indices. The report includes a literature review to determine the current state-of-the-art analysis of coal mine slope failures in the Australian context; analysis of laboratory data to look for trends in geomechanical properties relevant to basin or coal measures; laboratory testing of massive limestone and artificial materials to test upscaling assumptions; and investigations of the applicability of the Geological Strength Index (GSI) to slope instability and rock mass failure. This multi-authored report has several components which are presented in order of structure size. As the studied structure increases from small (laboratory size) to big (slope scale), and with the progressive inclusion of discontinuities at various scales, the rock and rock mass properties are revealed in this report. The final output of this study, GSIw, is a redevelopment of the GSI system for low strength rocks using back analysed slope failure cases.
Report B presents the application of numerical modelling. The Synthetic Rock Mass (SRM) numerical modelling method is presented as an alternative to an empirical classification system for forward-analysis of rock mass strength and deformability properties. The main advantage of SRM models is their ability to capture the domain-specific effects of heterogeneity and anisotropy that are not easily accounted for in the GSI system. A SRM model represents the rock mass as an assembly of rigid particles that are bonded at their contact points to form a Bonded Particle Model (BPM) with discontinuities superimposed via a Discrete Fracture Network (DFN) that has been generated from face mapping and/or downhole televiewer logs. As all elements of the rock mass are represented explicitly at the microscopic scale, the need for mathematically complex rock mass constitutive models is negated and realistic macroscopic failure mechanisms are emergent. To date, SRM models have seen limited application to coal mine slopes and this project sought to address this gap by developing SRM models for a large-scale slope failure case study from a Bowen Basin coal mine.