Underground » Environment - Subsidence and Mine Water
As an empirically-based discipline of engineering/science, subsidence engineering and its related risk assessment/management practices rely on the nature, quality, quantity and extent of subsidence monitoring data and, importantly, how the collected data are organised so that it can be accurately and effectively utilised.
After eight years of persistent efforts by a team of professional subsidence, mining and IT engineers directly employed or engaged as consultants by the NSW Resources Regulator, the project has produced the following outcomes.
- Establishment of a state-of-the-art web-based subsidence information resource called the “Standardised Subsidence Information Management System” (ie SSIMS). The System comprises a Data Submission Portal, a Subsidence Database and a Data Query Portal, supported by modern IT technologies and robust architectural and database design measures.
- Establishment of a substantial Subsidence Database as part of the SSIMS. As of 8 January 2019, the SSIMS housed 22,569 subsidence survey files that comprise a total of 1,082,350 subsidence survey data points obtained from monitoring grids above 533 extracted longwalls in NSW. The Subsidence Database will increase in size on an on-going basis as every operating longwall mine in NSW submits mining and subsidence survey data through the Data Submission Portal under the requirement of clause 67(2)(d) of the Work Health and Safety (Mines and Petroleum Sites) Regulation 2014.
- Delivery of a tangible product, ie the Data Query Portal, to the industry users and relevant regulatory agencies via the Internet, allowing them to interrogate the information stored in the SSIMS for the purposes of risk management, recovery of coal resources as well as risk-based regulation in relation to subsidence.
The established subsidence query facilities, accessible via the Data Query Portal, are supported by an innovative methodology developed by the project team, whereby each reading of a given subsidence parameter (ie vertical subsidence, compressive strain, tensile strain or tilt) is correlated with its likelihood within a defined query range. This approach is new to the conventional subsidence engineering. The quantifiable likelihood and its associated magnitude of a given subsidence parameter, as described above, will lead to improvement to risk management, recovery of coal resources as well as risk-based regulation in relation to subsidence.
Importantly, the above-mentioned subsidence query facilities provide quantifiable likelihood for the occurrences of abnormal subsidence which have been the core risks responsible for most of the subsidence incidents recorded in NSW. The likelihood of abnormal subsidence is determined subject to the magnitude of the maximum (of a subsidence parameter) predicted by the mine operator. An under-predicted maximum, observed previously from time to time in NSW, will lead to a higher likelihood of abnormal subsidence, which must be duly considered in risk assessment. It follows that strong debates on such under-predicted subsidence should not be necessary. Importantly, by focusing on the likelihood as well as its associated magnitude of subsidence, rather than the accuracy of the predicted magnitude in isolation, the methodology developed by the ACARP Project promotes significant industry cultural changes towards an improved risk-based approach to subsidence management.
Longwall extractions across all Coalfields in NSW (single seam only) have been divided into six groups according to the geometry of mine layouts. The query facilities have been established for each of the six longwall groups in relation to the key subsidence parameters, ie vertical subsidence, compressive strain, tensile strain and tilt.
The complex interactions between individual longwall panels have been addressed via a specially designed sampling procedure which works in the backend requiring no involvement of the users of the subsidence query facilities. A Users' Manual for the subsidence query facilities is available on the Internet as part of the SSIMS.
The project team have overcome some of the confusion associated with the conventional subsidence engineering and created new knowledge. The utilisation of a new concept, ie critical or super-critical longwall domains, to characterise the development of subsidence and to address the complex interactions between individual longwall panels, have led to the establishment of the innovative subsidence assessment methodology as described above.
The SSIMS, as described above, is unique in the world.
A Users' Manual, which outlines the procedures to gain access and to use the subsidence query facilities, is attached to Appendix C of this Report.