Underground » Strata Control and Windblasts
This ACARP project sought to demonstrate that significant improvements could be obtained in the up-time efficiency of longwall gate road development units by optimising roof support practices and utilising improved support technology. The project built on the results of earlier ACARP-sponsored projects (No. 3032 : "Roadway Roof Stability and its Attainment through Pre-Tensioned Bolting", ACIRL, 1995 and No. C4025 : Prestressing of Strands to Improve Cable Performance, BFP, 1997). The basic premise of this project was that reduction or removal, where possible, of support from the critical path of the development process would result in increases in development rate and/or reduced costs.
The project, greatly assisted by contributions from a large number of mine site personnel, gathered geotechnical and operational data from collieries covering a broad range of Australian situations, namely:
- sites in the Bowen Basin, Southern, Western and Newcastle Coalfields,
- depths of cover ranging from just over 100m to 500m, associated with low to high horizontal as well as vertical stress environments,
- coal, tuff, siltstone, laminite and sandstone roof measures, and
- methods ranging from simultaneous cutting and bolting to place changing.
The project then sought to optimise support practice, and examined the impact of support practice on productivity and costs.
The project has concluded that significant productivity gains can accrue from the rationalisation of support practice. Although the drilling and installation of a roof bolt only takes a few minutes, the total number of bolts installed over a given period, ie. a shift, tends to dictate overall operational productivity.
Improvements in development rates have assisted operations in to maintain continuity of longwall production and improving coal resource utilisation.
The benefits of improved and rationalised support practices go beyond productivity gains and direct cost savings. The project successfully demonstrated that the rationalisation of both primary bolting and secondary support practices could result in major overall reductions in material handling requirements. Not only does this reduce the demand on the transport and services function, it can improve the ergonomics of the bolting operation and reduce the risk of handling injuries. The project also successfully demonstrated that optimised support technology can improve aspects of roadway serviceability; the reduction or elimination of standing support in tailgates, for example, can result in improved ventilation.