Underground » Mining Technology and Production
The aim of this project is to provide the Australian coal industry with a roof support design methodology for longwall installation roadways (ie faceroads) that can be utilised by colliery engineers who have sufficient experience and training in relation to underground coal mine strata mechanics. This has been achieved and the design methodology (and software package) is referred to as Analysis and Design of Faceroad Roof Support (ADFRS). The intended benefits to underground operations, in the provision of this information and resource, are a safer and more productive workplace.
In relation to other strata control issues, such as coal mine pillar and roof support design (for standard roadway widths), there has been comparatively very little research undertaken in relation to the geotechnical design and management of longwall installation roadways. As a result, in terms of a satisfactory outcome, faceroads within Australia have been quite problematic and by way of example of the 207 cases associated with the two-pass dataset, 40 resulted in an unsatisfactory outcome involving the use of standing support, PUR and/or high levels of remedial tendon support with two faceroads 'lost' and having to be re-driven due to major roof falls.
The authors were also aware of several other faceroads that were abandoned in recent years due to major roof falls however due to a lack of site specific information, they could not be included in the database. Nonetheless a failure rate of approximately 20% is judged to be unacceptable. The authors' contend the principal reason for such a failure rate is the clear absence of suitable design equations that relate the required levels/type of roof support as a function of the competency (or some valid measure of the competency) of the roof and the horizontal stress acting across the roadway.
ADFRS now fills the gaping void that existed in the Australian underground coal industry with respect to the geotechnical design and management of longwall installation roadways. ADFRS is based on a sound mechanistic understanding of the roadway development and widening process and the design equations (with strong to very strong correlations) are fully consistent with measured roof behaviour.
Over the last two decades (particularly subsequent to the findings associated with the Moura disaster in 1994, ie Windridge, 1995), many aspects of strata management have evolved, such that risk management has become the "core" of the strata management process at most Australian collieries. This is borne out with the advent of strata management plans, roadway and longwall hazard plans and in relation to ground support, the categorisation of various zones as a part of the Mine Manager's Support Rules.
The ADFRS design methodology has been formulated to complement the mine site risk management approach to strata control/management. However because there are factors affecting longwall installation roadway behaviour that are either specific to or more pronounced at an individual colliery, it is imperative that the ADFRS design recommendations, resulting in the formulation of a ground support design strategy, be assessed within the framework of a properly facilitated mine site risk assessment and that a properly considered TARP is in place prior to any development taking place.