ACARP Project C12007 - Fitness for Purpose of Powered Roof Supports - was undertaken by the University of Queensland. This project developed a concept to characterise load cycles of longwall shields which enabled most of the interaction between a longwall support and the roof to be quantified. A characteristic load cycle is the change in support pressure with time from setting the support against the roof to the next release and movement of the support. The concept was validated through the back-analysis of more than 500,000 individual load cycles in five longwall panels at four mines and in seven geotechnical domains.

The validation process depended upon the development of new software capable of handling the large quantity of data emanating from a modern longwall and accurately delineating load cycles. Load cycle analysis can now be used quantitatively to assess the adequacy of support capacity and the appropriateness of set pressure for the conditions under which a longwall is being operated. For existing sites, the load cycle characteristic concept allows for a diagnosis of strata-support problem areas, enabling changes to be made to set pressure and mining strategies to better manage or avoid strata control problems.

Currently, the computer program is suited only for use at the research level and can only be used for uni-directional cutting and 2 leg supports. Also the existing code can only be applied to historical data.

The current project addresses these issues and aims to develop a real-time analysis system. In this project, four maps of critical load cycle features, generated by the software developed during C12007, are used to understand how well the supports and the set pressures being achieved are coping with the mining conditions.

• The first map shows time-weighted average pressure in each leg and provides a general indication of the severity of the roof loadings.
• A second map shows the number of yield events experienced by each leg within a loading cycle and indicates when supports do not have an adequate capacity for the conditions. Yielding is obviously associated with support convergence and can be expected to lead to deterioration of roof conditions if it continues throughout the cycle, particularly those of extended duration. Time is often a critical component in the optimum operation of a longwall. For example, it is possible to mine successfully through periods where the supports are overloaded, provided cycle times for each support are kept to a minimum.
• A third map shows cycle times.
• A fourth map identifies regions where the set pressures are regarded as too low for the conditions. Deterioration of roof conditions can often lead to difficulties in setting the supports to a pressure that will adequately support the roof. Poor roof conditions are generally exacerbated when only relatively low set pressures are achieved.

The rate of loading throughout all or part of the loading cycle was also found to be a good indicator of how the support was interacting with the strata and it is proposed to develop a map of this load cycle feature.

With a rapid response analysis system, it should be possible to identify the build-up of periodic weighting events and avoid stopping under high loading conditions that result in overloaded supports. It should likewise be possible to rapidly identify when set pressures are too low for the conditions and initiate increases in support set pressures. The rapid identification of faulty support components should reduce incidents of roof control problems even where loading conditions are reasonably favourable. Roof support problems will be mitigated to maintain high performance of the longwall as a whole.

Contact Information
Isles Road, Indooroopilly, Qld Australia 4068
Phone:+61 7 3365 5888
Fax:    +61 7 3365 5999
Email: jkmrc@uq.edu.au