A case study of large scale rock mass preconditioning by confined blasting

A number of caving operations are expected to be in deposits or geological systems located at much greater depths than current. These deposits are characterised by strong rock masses and higher stress regimes. These conditions will impose greater technical and mining challenges and therefore risks in terms of the caving processes, cave establishment and subsequent production. In order to mitigate such potential risks, rock mass “preconditioning” techniques are being implemented into mine design and planning. The term “preconditioning” has been adopted within the mining industry to describe the process of “modifying” a rock mass to enable better control or management of the cave mining process. It is currently achieved through techniques such as hydraulic fracturing, confined blasting or a combination of both. This paper summarises the results of a comprehensive geotechnical; monitoring and advanced blast modelling program involving large scale confined blasting tests at the first of a series of panel caves in the Cadia East mining complex in New South Wales, Australia. One of the objectives of this program was to obtain information to calibrate and evaluate the application of a newly developed explosive-rock interaction model. Results from the modelling work were used to understand the complex mechanisms at play under fully confined blasting conditions. In addition they helped identify improvements in explosive charge initiation and blasthole layouts to enhance the extent of rock mass preconditioning within the existing mining geometry and production constraints