The block cave mining method takes advantage of the effects of gravity by undercutting the rock mass until it caves through the height of the undercut. The resulting relatively minor movement of the rock mass is usually sufficient to break it into fragments. The use of gravity in such a manner results in caving being a low cost mining method. The main reason for this economical efficiency is that the amount of blasting that is required in comparison to other mining methods is reduced through the use of the block caving method. These economical benefits have brought into consideration a wider range of rock masses as candidates for the method. Knowledge of these rock masses, together with the conditions imposed upon them, are significantly outside the range of current experience.
Ore fragmentation has a great influence on the performance of a block caving mine. The effectiveness of the design of the mining layout as well as many significant operational procedures depend ultimately on the accuracy of the initial fragmentation estimates.
Fragmentation in block caving mines comprises three consecutive levels. These levels of fragmentation are in situ, primary and secondary. There is a natural progression from the pre-existing in situ blocks to the resulting secondary blocks reporting to the drawpoint. During the caving process, the blocks that separate from the rock mass represent the primary blocks.
The features governing the natural fragmentation of a rock mass are the discontinuities within it. These discontinuities within the rock contrast the material from most other materials that engineers contend with and have a dominant effect on the response of a rock mass to mining operations. This thesis presents the framework and application of a fundamentally-based method, known as JKFrag, for fragmentation prediction in block caving. The basis of this method is the application of a rigorous tessellation procedure, namely a Delaunay triangulation, to a rock mass discontinuity model and the utilisation of the discontinuities as edge constraints in the tessellation.
This method provides the means to relate the discontinuities as a network and to efficiently define and measure the closed and partially closed spaces within a rock mass discontinuity model. In this application, the closed spaces represent blocks and the partially closed spaces represent the intact rock bridges which contribute to the stability of the rock mass. As there is a natural progression through the initial stages of fragmentation in block caving, the framework and data structures of the model logically renders the basis upon which this progression can be simulated.
The applicability of the developed model to in situ and primary fragmentation is demonstrated and key issues relating to the modelling of secondary fragmentation are discussed.