Background review Subsidence from coal mining activities This background review was commissioned by the Department of the Environment on the advice of the Interim Independent Expert Scientific Committee on Coal Seam Gas and Coal Mining. The review was prepared by Sinclair Knight Merz Pty Ltd and revised by the Department of the Environment following peer review. June 2014 Background review: subsidence from coal mining activities Copyright © Copyright Commonwealth of Australia, 2014. Subsidence from coal mining activities, Background review is licensed by the Commonwealth of Australia for use under a Creative Commons By Attribution 3.0 Australia licence with the exception of the Coat of Arms of the Commonwealth of Australia, the logo of the agency responsible for publishing the report, content supplied by third parties, and any images depicting people. For licence conditions see: http://creativecommons.org/licenses/by/3.0/au/ This report should be attributed as ‘Subsidence from coal mining activities, Background review, Commonwealth of Australia 2014’. The Commonwealth of Australia has made all reasonable efforts to identify content supplied by third parties using the following format ‘© Copyright, [name of third party] ’. Enquiries concerning reproduction and rights should be addressed to: Department of the Environment, Public Affairs GPO Box 787 Canberra ACT 2601 Or by email to: [email protected] This publication can be accessed at: www.iesc.environment.gov.au Acknowledgements This background review was commissioned by the Department of the Environment on the advice of the Interim Independent Expert Scientific Committee on Coal Seam Gas and Coal Mining. The review was prepared by Sinclair Knight Merz Pty Ltd with input from Don Kay and revised by the Department of the Environment following peer review by Professor Joan Esterle (University of Queensland) and relevant Queensland, New South Wales and South Australian Government departments. Disclaimer The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment or the Interim Independent Expert Scientific Committee on Coal Seam Gas and Coal Mining or the statutory Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development (IESC). While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Commonwealth and IESC do not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication. Addendum Changes to state government departments have occurred since the finalisation of this report by the authors. The Queensland, New South Wales and South Australian Government agencies were contacted and updated information provided in September 2013; however, no guarantees can be made as to the completeness of these updates. Up-to-date information should be sourced from the relevant department. page ii Background review: subsidence from coal mining activities On 1 January 2013, the Queensland Water Commission (QWC) ceased operations. The Office of Groundwater Impact Assessment (OGIA) retains the same powers as the former QWC under Chapter 3 of the Water Act 2000 (Qld). Sinclair Knight Merz Pty Ltd is now Jacobs SKM. page iii Background review: subsidence from coal mining activities Contents Copyright .............................................................................................................................................. ii Acknowledgements .............................................................................................................................. ii Disclaimer ............................................................................................................................................. ii Addendum ............................................................................................................................................ ii Summary ................................................................................................................................................. vi Abbreviations ........................................................................................................................................... x Glossary.................................................................................................................................................. xii 1 Introduction ......................................................................................................................................... 1 1.1 Background to the report ............................................................................................................ 1 1.2 Underground coal mining in Australia ........................................................................................ 1 2 Subsidence due to coal mining .......................................................................................................... 3 2.1 Underground coal mining methods ............................................................................................ 3 2.2 Underground mechanisms causing subsidence ...................................................................... 10 2.3 Subsidence profile .................................................................................................................... 12 2.4 Subsidence parameters ........................................................................................................... 13 2.5 Surface subsidence development ............................................................................................ 16 2.6 Factors influencing mine subsidence ....................................................................................... 18 3 Predicting subsidence due to coal mining ........................................................................................ 25 3.1 Empirical prediction methods ................................................................................................... 25 3.2 Analytical or numerical prediction methods ............................................................................. 26 3.3 Assessing potential impacts of subsidence due to coal mining ............................................... 28 4 Monitoring subsidence induced by longwall coal mining ................................................................. 31 4.1 Ground survey methods ........................................................................................................... 31 4.2 Remote sensing methods ........................................................................................................ 32 4.3 Sub-surface subsidence monitoring in boreholes .................................................................... 33 5 Minimising and remediating subsidence induced by longwall coal mining ...................................... 38 5.1 Panel backfilling ....................................................................................................................... 38 5.2 Grouting .................................................................................................................................... 38 5.3 Panel and pillar extraction ........................................................................................................ 39 6 Coal mining subsidence regulations ................................................................................................ 40 6.1 New South Wales ..................................................................................................................... 40 6.2 Queensland .............................................................................................................................. 41 7 Review of findings ............................................................................................................................ 42 7.1 Past and current subsidence research .................................................................................... 42 7.2 Subsidence investigation methods .......................................................................................... 42 7.3 Differences between data and research in New South Wales and Queensland ..................... 43 page iv Background review: subsidence from coal mining activities 7.4 Key findings .............................................................................................................................. 44 8 References ....................................................................................................................................... 46 Appendix A: longwall mining in New South Wales and Queensland .................................................... 50 Appendix B: Southern Coalfield subsidence controversy 1900 to 1974 ............................................... 55 Appendix C: detailed assessment of geological factors influencing subsidence .................................. 58 Appendix D: the incremental profile method for subsidence prediction ................................................ 64 Appendix E: case studies ...................................................................................................................... 66 page v Background review: subsidence from coal mining activities Summary This report