Open Cut » Rock Mechanics
The aim of this project was to calculate tensile strength indices derived from comminution tests on uniform, non-standard size samples of coal measure rock types that include sandstone, siltstone and claystone. A methodology has been developed that permits estimation of material strength for thinly bedded rock units that are not amenable to conventional strength tests. Furthermore, this contributes towards rock mass strength characterisation processes as inputs for mine design.
The project deliverables are:
- Calculation of empirical correlations between the Short Impact Load Cell (SILC)-measured tensile strength and Brazilian Tensile Strength (BTS) to enable a rapid, small-scale geotechnical method to characterise tensile strength of coal measure rock types, including thinly bedded lithological units.
- An improved understanding between rock characteristics and tensile fracture propagation.
- A refined methodology for sample selection, preparation and testing to enable a reproduceable method for characterising rock strength. A practical guideline for conducting SILC-based tensile strength estimation from thinly bedded coal measure rock types was produced.
These three deliverables were based on testing using the SILC device on 1,112 cylindrical samples of sandstone, siltstone and claystone at 4 size fractions (8 to 16 mm in diameter) and with fabric orientated both perpendicular and longitudinal to the core axis of the sample. An additional 87 repeat samples formed part of the QAQC procedure. Rock type and texture were derived from a combination of visual logging, high-resolution photography and point hyperspectral mineral interpretations. Standard BTS (50 mm diameter) geotechnical tests were performed on 15 sandstone and 12 siltstone samples, and miniaturised BTS (16 mm diameter) on 41 sandstone and 28 siltstone samples for comparison.