Underground » Strata Control and Windblasts
The Australian underground coal mining industry consumes 5 to 6 million rock bolts per annum. It has been independently concluded that between 30%-35% do not perform to specification. This represents an annual expenditure of $35-$40 million. There are no standardised methods for assessing rock support consumables, installation techniques and support behaviour. The actual anchorage and failure mechanisms of resin anchors have yet to be adequately quantified, with rock support systems primarily evolving from an experience base rather than a knowledge base. A need exists to develop this engineering knowledge base.
The research was concerned with:
- Establishing a rockbolt testing facility in Australia that addresses many of the problems and limitations associated with past research efforts into rockbolt anchorage and failure mechanisms.
- Utilising this new testing facility to establish standard laboratory testing procedures for both rockbolt support components and rockbolt support systems.
- Advancing the understanding of the anchorage and failure mechanisms of fully encapsulated rockbolts.
- Fostering national and international collaboration between researchers in the field of rockbolting.
This End of Grant Report summarises the theses of the two students and supplementary research. An Honours thesis has been based on:
- A literature review to establish the range of testing procedures utilised by researchers and the outcomes of this research.
- Numerical modeling to establish whether the mechanics associated with applying load to a rock bolt in field testing or laboratory testing is representative of the in-situ loading environment.
A Masters thesis based on a two-staged research program followed the Honours thesis. In the first stage, a literature review was undertaken that focused specifically on the anchorage mechanisms associated with fully encapsulated rock bolts. A prototype rock bolt testing facility was established and a number of preliminary tests were conducted to calibrate the facility and to evaluate the proposed testing procedures.
- The second stage of the research encompassed modifications to the test facility and test procedures, development of a range of new tests, and introductory research into some of the parameters found to influence load transfer during the stage 1 research. Stage 2 testing examined the performance of both individual components and the overall system associated with resin encapsulated bolts.
The outcomes of this testing program should be considered preliminary since they are based on a limited number of tests associated with developing and evaluating a standardised rock bolt testing facility. Many will be re-evaluated more precisely when the research resumes under a new ACARP grant to take effect in early 2001. However, they do give insight into some of the complexities associated with testing and understanding the anchorage mechanisms of fully encapsulated rock bolts. The more significant findings to date include:
The data being generated by the UNSW rock bolt testing facility is the subject of considerable discussion between some areas of the research and consulting community. This is particularly so in regards to the correlation being measured between the applied axial bolt load and the lateral pressure change measured in the surrounding rock mass once the encapsulation medium yields. It needs to be established if this is simply a Poisson's effect, or a response to the confining action of deformed ribs on a rock bolt or a combination of both. Investigations have been ongoing into this since the completion of the ACARP project and some developments are presented in this report.
A noteworthy feature of the research has been the successful collaboration between national and international researchers, consultants and strata product companies in the field of rock bolting. This collaboration has stimulated and advanced the knowledge base and has been a valuable source of both technical advice and rock bolting consumables.