A number of new mining methods, such as LTCC and wider faces, have ramped up this year in Australia. What are the ramifications of this now and in the long term?
The primary driver associated with new mining methods has been to increase the longwall recoverable tonnes per metre of gateroad development in addition to increasing resource recovery. This is particularly the case for Longwall Top Coal Caving (LTCC).
In the case of widening longwall faces although there numerous instances of faces in excess of 300m successfully operating in the US, until recently this has been unprecedented in Australia. Recent experience at Oakey No 1 and Ulan has been positive.
The benefits associated with widening faces in the context of economies of scale, including the shorter term benefits associated with increased shears per shift and reduced flitting are self evident. The benefits however, need to be balanced against potential constraining impacts including maintenance requirements associated with the increased number of shields and the increased physical distances associated with repairing or replacing equipment on a wider face.
The geotechnical environment associated with widening faces also needs to be carefully considered. Increased panel widths will tend to increase the abutment load on chain pillars, particularly on the maingate chain pillar in cases where the maingate is located down dip of the tailgate (normally the case in mine planing to minimise gas ventilation impacts). Longwall abutment or face load impacts may be exacerbated dependent on the nature of the overburden strata (particularly overlying massive strata), and the subsidence caving profile dependent on panel width and cover depth. Potential geomechanical impacts should not necessarily be considered constraints as long as each mine planning case is considered unique and requiring discreet mine planning and operational controls.
With respect to Longwall Top Coal Caving, Chinese experience has demonstrated that the method enables up to 80% of “thick” seams in the 5m – 9m thickness range to be recovered. On this basis there are many thick seam resources in Australia which have the potential for LTCC extraction. Increasing cutting height to maximise seam recovery through single pass shield extraction can be detrimental due to the increased propensity for slough from the immediate face, thereby increasing tip to face distance and the potential for cavity development.
In this context, maintaining an extraction profile consistently at a (relatively lower) height during LTCC has the potential to minimise geotechnical impacts and maintain consistent productivity. If the geomechanical profile and caving conditions suit, LTCC will likely and justifiably become the preferred and optimal method of Australian thick seam recovery in the coming decades.
Looking into the future, punch longwall mining from existing highwalls will continue to present opportunity and multi seam extraction and thin seam extraction using alternative methods including plowing have huge potential in Australian underground coal resources. There are particular advantages associated with the extraction of thin high quality seams in resources which may previously have been overlooked or constrained on the basis of seam thickness.
A number of junior and mid-tier coal explorers and producers are currently carrying out exploration, feasibility studies and bringing mines onto line. What does this mean for consultants, and for the Australian industry as a whole?
IMC has been involved in the supervision and coordination / project management of a number of exploration programs carrying this through to mine planning and project development for junior and mid-tier coal explorers in recent times. Maintaining a single project team to design an exploration program, undertake mine planning, resource and reserve assessment on behalf of a client has distinct contractual advantages for the Client in the context of on-running accountability and in streamlining communication and data transfer for all aspects of the staged process.
IMC consider that increasingly, junior and mid tier clients may perceive an advantage in maintaining a single source project management group, providing there is adequate experience and capability, to manage these processes and assist in directing strategy. Beyond completion of a Bankable Feasibilty Study, there is merit in utilising the mine planning team to assist clients in on the ground development of projects and operational management. The continued transfer of acquired local knowledge and accountability from exploration to mine planning, particularly the conversion of resources to reserves and ultimately project development remains essential.
In your eyes what is the most important R&D project (private or publicly funded) happening at the moment and why?
The most important R&D project in IMC’s view is the research currently being undertaken by the Australian Coal Association in developing Clean Coal Technologies in Australia, improving the efficiency of power and the development of new ways of using coal, including gasification. Australia has the potential and the resources to lead the world in these technologies and there is no more immediate and pressing requirement for all stakeholders to secure the longer term viable future of Australian coal extraction and utilisation.
What progress has been made in improving the way roof falls are managed?
On site hazard management and Strata Control Hazard Management Plans have unquestionably had a beneficial impact in minimising the potential for roof / rib failure through improving the communication of hazardous areas in advance of mining, conditional monitoring and triggering suitable responses. Appropriate training and communication to the face crews to understand the nature, relevance, required monitoring and response to particular hazards has assisted in minimising the potential for roof / rib failures.
The impact of geological structure including faults, folds and rider seam splits remains a key component in many roof falls and there is a critical link between the identification of interpreted structure (be it for example mapped across strike from previous exposure or interpreted from geological modelling or seismic interpretation) and clarity of communication of assessed risk and required response in advance of mining. In addition, recognising any changes to the geomechanical or mining environment such as increased potential for stress or weaknesses associated with cover depth, inconsistent mine layout dimensions or the proximity of infrastructure requires similar controls and responses. Real time pressure monitoring and convergence systems on a longwall face have helped in identifying and responding to problem areas.
Defining precisely Who, What and importantly When required responses should be triggered has in IMC’s operational experience proven to be effective in minimising the potential for roof and or rib failure. This is the case on both on development and under the impact of abutment loading.
