Underground Thick Seam Mining: Old Problems, New Technologies

In Australia, single pass longwall is the most favoured method of extracting coal from 4.5m to 6m thick seams.  More than six billion tonnes of measured underground mineable coal reserves in Australia exist in thick seams (more than 4.5m) in difficult geological conditions. Often, mining thick seams results in poor resource recovery and high hazards levels. Hazards have included rib and roof control (due to height and accessibility), pillar stability, spontaneous combustion (due to ventilation difficulties and quantity of slack coal).

Project Objectives

The objective of the project was to undertake a critical appraisal of thick seam mining opportunities, taking into account:

• Improved geotechnical understanding of the driving mechanisms controlling and constraining particular mining systems
• Rapid development of mining equipment and monitoring/control technologies
• Constraints on different mining methods due to hazard management imperatives (ventilation, gas, dust and spontaneous combustion)
• Increasingly available and sophisticated levels of remote control and progressive use of automation

Outcomes

The project work includes:

• Establishing an updated review of international underground thick seam mining methods and experience
• Reviewing each method to identify particular features and constraints which might limit its application in the Australian mining industry
• Developing a detailed database of Australian underground coal reserves to categorise the potential thick seam reserves according to parameters that might affect the choice of mining method
• Linking the database with the matrix of mining methods and critical parameters (especially geotechnical and other operational parameters) to determine a priority listing of appropriate methods for Australia.

Findings

Single pass longwall is the most favoured option for the 4.5m to 6m thick seam range, but is unlikely to be extended to greater than 6m height within the next 10 to 15 years. Alternative methods must be developed.

Methods such as multi-slice longwall, caving methods and hydraulic mining do warrant further investigation. Subject to appropriate geotechnical, equipment and monitoring/control technologies being developed, these alternative methods may find application in Australia within 15 years.

Where To From Here

Recommendations from this research have led to a sequel ACARP project, titled "Technology and Feasibility of Potential Underground Thick Seam Mining Methods" which started in April 1999. The project focuses on the priority mining methods identified in this study:

• Single pass longwall
• Multi-slice descending longwall
• Hydraulic mining
• Caving (soutirage) methods.