Evaluation of intensive preconditioning in block and panel caving – part II, quantifying the effect on seismicity and draw rates

Abstract

A combination of preconditioning by hydraulic fracturing and confined blasting referred to as intensive preconditioning was implemented at a major panel caving operation. The aim is to alter rock mass behaviour in a manner that could improve caving mechanics and extraction performance. A benchmark study involving data collected from operations in Chile, South Africa and Australia was carried out to investigate the hypothesis that operational data such as induced seismicity and draw rates could provide a quantitative measure of the impact of different preconditioning techniques. Analysis using Gutenberg and Richter (G–R) curves indicated that a massive and competent rock mass without preconditioning presents an induced-mining seismicity behaviour that is less favourable than a rock mass with intensive preconditioning, in other words, seismic events were shown to be more regular, numerous and their magnitudes higher than in the case where intensive preconditioning was applied. From draw rate data, analysis showed that the application of intensive preconditioning could improve draw rates by 15–28%, with relative differences of up to 38%. It is also important to note that this improvement in performance is achieved in a confined condition and at depths relatively greater than most block and panel caving operations.

Keywords:

• Intensive preconditioning
• hydraulic fracturing, confined blasting
• block and panel caving
• intact rock strength assessment
• acoustic emission
• damage stress thresholds
• microseismicity
• seismic behaviour
• draw rates
• caving propagation rates
• caving performance

Acknowledgments

This study formed part of the principal author’s PhD thesis (Catalan 2014) supported by the WH Bryan Mining and Geology Research Centre of the Sustainable Minerals Institute at The University of Queensland, Brisbane Australia and Newcrest Mining Limited.