Fundamental principles of an effective reinforcing roof bolting strategy in horizontally layered roof strata and three areas of potential improvement

It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times primarily due to the prevailing industry view that few, if any further improvements can be made to the current state of the art. On the contrary, this paper will contend that reinforcing roof bolting systems can be further refined by considering both the specific manner by which horizontally bedded roof strata loses its natural self-supporting ability and the specific means by which reinforcing roof bolts act to promote or retain this natural self-supporting ability. The Australian coal industry’s seeming insistence on minimising bolt-hole diameter to maximise load transfer and targeting full-encapsulation by any means has led to a significant, albeit unintended consequence in terms of overall roof bolting effectiveness, namely the promotion of increased resin-pressures during bolt installation and the associated potential for the opening up of bedding planes that may otherwise remain closed during the bolt installation process. Given that the natural self-supporting ability of roof strata is strongly linked to whether bedding planes remain open or closed, it stands to reason that minimising resin pressures should be of significant benefit. Three issues are primarily focused on three key issues that relate directly to the function of the roof bolting system itself, namely: (i) the importance of proper resin mixing in the context of maximising load transfer strength and stiffness, (ii) the importance of minimising resin pressures developed during bolt installation and (iii) the importance of maximising the effectiveness of the available bolt pre-tension. The logic being that if: the reliability of resin mixing with varying hole diameter is substantially improved, if resin pressures generated during bolt installation are substantially reduced, if the length of the bolted interval directly influenced by high resin pressures generated during bolt installation is substantially reduced, and if roof bolt pre-tension levels are increased, why wouldn’t individual roof bolt effectiveness and thus roof reinforcement improve? The potential benefits to the mining industry of improving the individual effectiveness of each installed roof bolt, even by relatively small incremental amounts, should be of interest to all mine operators and is an important topic for discussion amongst the mining community.