Fitness for purpose of longwall powered supports

Abstract

Powered supports account for the majority of the capital expenditure for a longwall panel and are fundamental to the success of the operation. The adequacy of the support capacity for the geotechnical and geological conditions that will be met during mining and the set pressures can significantly impact upon ground control and equipment life.The research has developed a new geotechnical model of the support roof-strata interaction process that links support load-time characteristic patterns observed during longwall operation to geotechnical and mining conditions. The model permits determination of the adequacy of the support and appropriateness of the set pressures for the conditions. This new model was developed after an extensive study of the existing methodologies for support capacity selection had concluded that they were all fundamentally flawed or oversimplified and therefore ineffective.The geotechnical model links a standard classification of the roof conditions to expected loading patterns. Its application to a variety of mining conditions lead to the development of the basis of an empirical database which has the potential to be expanded and used as a tool to estimate the support requirements and operating strategies that will be effective in a greenfields situation. The research programme made detailed studies in 5 mining panels at four mines. It is estimated that 67% of the range of extraction heights and 62% of the range of depths of cover presently being mined in Australia have been analysed and the corresponding support capacity and set pressure used have been assessed. Likewise, 40% of main and immediate roof classification combinations have been studied. The research relied upon analysis of support loading cycles for every support in the face over a total advance at all the mines of 1,590 m. Approximately 500,000 loading cycles were analysed. This analysis was made possible by the development of new software in a concurrent ACARP research project (Trueman et al, 2005) that accepts the raw data files from longwall monitoring systems and makes accurate (>95%) identification of the loading cycles. The software calculates face advance and was typically in error by only one or two metres in 150 m of advance even in worst case scenarios. While the software was operated on historical data files during the research, with some further development it could be operated in near real-time. The new software was developed after trials of existing software such as 'Shields' demonstrated that they were not capable of correct load cycle delineation. The extensive data analysis, which included a detailed study of mine geology and operating conditions in the areas of support data logging, has provided the basis for a comprehensive validation of the geotechnical model. In all areas studied, the loading patterns expected from the geotechnical analysis were observed. In addition to an assessment of support-strata interaction for normally operating supports, the impact of faulty support components on roof conditions was able to be determined. Faults on even a few isolated supports were found to potentially lead to localised ground control problems and costly production delays. The software can be used to identify these faulty support components. Immediate positive outcomes of the research were the identification and quantification of problem areas at the sites where analyses were carried out and recommendations as to the best way to avoid or alleviate the impact of these problems. ........