Underground » Mining Technology and Production
Although longwall mining is the principal source of coal from Australian underground mines, the geomechanics of rock failure around an operating longwall has not been clearly understood. In recent years, there have been significant events at many longwall mines associated with this knowledge gap that have had a severe impact upon longwall productivity. Through a series of investigations, with extensive field studies at 13 sites, the CSIRO has been able to substantially define the controls on LW geomechanics in both qualitative and quantitative terms.
This project has conducted field investigations at three Central Qld mines. The results of these individual investigations have been reported progressively to each minesite and Kenmare and Southern are contained electronically on the final report CD. The summary report, also gives an overview of the issues and outcomes at each of these three sites. In addition, the summary report reviews previous literature and approaches to longwall geomechanics, describes the CSIRO approach and some of the technologies that have been developed through the project, and combines experience from all of the work to date to describe 3D controls on longwall geomechanics. The project has been acknowledged as being a world leader in defining 3D mechanisms for a wide range of longwall environments. The project has been successful in developing new assessment technology that will enable longwall mines in Australia and elsewhere to better determine geotechnical risk and solutions to specific site issues.
The assessment approach advocated by CSIRO is a broad based approach that relies on the utilisation of several independent technologies. The use of these independent technologies provides cross validation and increased confidence in mechanisms and recommended corrective action defined in this process.
As well as the combined use of these technologies, the site studies have highlighted two important areas that require an increased focus in site strata control management plans:
- improved geological/geotechnical assessment; and
- face control.
On every site the geological characterisation has been a key requirement. On many occasions some initial glossing over or averaging of the geology has occurred. This has invariably led to unexplained issues which are only explained when the geology and rock properties are studied in more detail.
Face control management using chock pressure analysis is essential if mines are to address many problem areas. In many cases, it has been found that poor operating methods and face maintenance procedures have resulted in low setting or yield loads. This can result in many of the face problems that the mine is trying to solve.