Geomechanical behaviour and deformation of coal mine roof strata around faults: toward an engineering geological model

The development of an accurate engineering geological model and adequate knowledge of spatial variation in rock mass condition are important prerequisites for mine planning and risk management in underground coal mines. In longwall mines in particular, evaluating and predicting geomechanical features and rock conditions ahead of mining is critically important because panel extraction is somewhat inflexible. Good longwall face conditions often depend on continuous production and concomitant goaf collapse. This thesis examines aspects of how faulting and rock mass conditions can be evaluated at underground coal mines, using a Bowen Basin coal mine (Carborough Downs) as a case study, and then situating these results into a regional and global context. A mine-wide analysis of faulting was undertaken, and compared with in situ stress field and local-scale measurements of joint and cleat at two sites. Results indicate that a range of faulting styles including normal and reverse faulting are prevalent across the mine, with the dominant discontinuities in the target Leichhardt coal seam limited to butt and face cleat, in addition to other joint populations pervading the overlying and underlying siltstone and sandstone strata. In particular, principal horizontal stress axes coincide with the strike of face cleat. The large-scale structural geology has affected the engineering geology and influenced mine panel layout. Rock mass classification was also undertaken at 68 sites across the mine using rock mass rating (RMR), coal mine roof rating (CMRR), roof strength index (RSI) and the Q-system. Both the Leichhardt Seam and overburden rock show marked spatial variability in terms of RMR, CMRR and Q, but RSI showed limited sensitivity to changes in rock mass condition. Relationships were developed between different parameters with varying degrees of success. While there are no clear relationships between rock mass classification parameters and faulting, a central graben zone shows heterogeneous rock mass properties. A fracture aperture-spacing analysis was undertaken in varying proximity to faults, and the fracture aperture-size scaling laws apparently replicate power-law relationships identified in other studies. However, it was found power-law equations of fracture “intensity” need to be interpreted carefully, and a refinement is proposed to the previous method in which such power-law scalings have been to applied as measures of fracturing “intensity”.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2016

Author dc:creator

• Brook, Martin

• Geotechnical
• Coal mine
• Strata control
• Longwall
• Bowen Basin

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/2972

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/56079