Chain Pillar Design (Calibration of ALPS)

The aim of this project is to provide the Australian coal industry with a chain pillar design methodology and computer based design tool that can be utilised by engineers and geologists who have sufficient experience and training in relation to underground coal mine strata mechanics.

The starting point or basis of the project is ALPS, ie Analysis of Longwall Pillar Stability developed by the United States Bureau of Mines (USBM). The ALPS methodology uses tailgate performance as the determining chain pillar design criteria. The work program undertaken to calibrate ALPS for Australian conditions firstly involved the establishment and empirical review of an Australian database. Secondly, several instrumented chain pillar and tailgate monitoring sites were utilised to help characterise the chain pillar loading environments and tailgate performance.

It was found that a satisfactory design methodology was possible based solely on the empirical analyses of the database. However the monitoring sites assisted in refining the design methodology and identified some chain pillar loading environments where there was significant divergence to that proposed by ALPS.

The design methodology proposed by this study will be referred to as ALTS - Analysis of Longwall Tailgate Serviceability. It is assessed that the main goals of the project have been fulfilled, those being:

1. To establish a chain pillar design methodology that has widespread application to Australian longwall operations.
2. To quantify the variance in the chain pillar loading environment between collieries and mining localities and to incorporate this variance within the design methodology.

In addition, the study has been able to propose definitive guidelines in relation to the installed level of primary support and to conduct a subjective analysis regarding the impact of standing secondary support on the design process. This provides the Australian coal industry with a truly integrated design methodology, in relation to tailgate serviceability, that has been able to address most of the main factors controlled by the mine operator.

It is anticipated that the initial benefit from this study is that oversized chain pillars and unnecessary roadway driveage can be rapidly eliminated from our industry. Mine managers and strata control engineers will be able to make these reductions with the confidence that a credible Australian database is the foundation for the design methodology.