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Microseismic Analysis in Caving Prediction

20ASC and Itasca Consulting Group, Inc. (the Minneapolis office of HCItasca) are continuing a long tradition of collaboration as joint research partners in the Mass Mining Technology (MMT) Project, an industrially-funded project supporting fundamental research into the mechanics of caving, blasting and flow in underground mass mining. The strength of collaboration between ASC and Itasca lies in the ability to study fundamental modes of rock fracture, using the Particle Flow Code (PFC) to create and test "synthetic rock" and comparing the predicted spatial and temporal trends in fracturing directly with microseismic data obtained in the laboratory or field. This represents a powerful combination of tools that can be applied to a wide range of rock mechanics problems. The technique has been successfully employed within pioneering research projects to reproduce in situ seismicity measured in massive brittle rock (Hazzard and Young, 2004) and has been applied to the analysis of damage around underground excavations (Young et al., 2004).

The primary objectives of the MMT research are to extend the technique to the prediction of jointed rock mass behaviour in three dimensions, to use this in the development of improved tools for prediction of cave growth, fragmentation, and subsidence and to extract more value from microseismic data in caving prediction and monitoring. At the core of the new methodology is the construction and testing of "Synthetic Rock Mass" (SRM) samples for predicting rock mass behaviour. SRM samples are three-dimensional and simulate rock as an assembly of bonded spheres (intact rock) with an embedded discrete network of discshaped flaws (joints).

The Lift 2 block cave at Rio Tinto's E26 Mine in Southeast Australia has been employed as a case study to test the potential for application of SRM technology and advanced microseismic analysis to caving prediction. ASC employed a number of novel microseismic data techniques that enhance the information currently retrieved from microseismic catalogues to develop an understanding of the fracturing and yield that accompanied undercutting and caving at a case study block cave. Through a series of analyses, cave-induced microseismicity showed its potential to provide further insight into the fracture network (interpreting existing seismic parameters in terms of fracture clustering, preferred orientation, size and spacing) and its correlation with different factors present in the production environment.

Itasca constructed a number of SRM samples for the various geomechanical domains at the mine and subjected them to representative cave-induced stresses. The tests provide a significant volume of information including fracture orientations, rock mass modulus, strength, brittleness and fragmentation. Comparison of the predicted and in situ fracture modes and orientations derived from the microseismic catalogue indicated very similar trends and represented a significant validation of the SRM approach.

ASC and Itasca thank the sponsors of the MMT project for the opportunity to conduct this fundamental research. We see significant potential for the application of Synthetic Rock Mass testing and linked microseismic analyses to other mine design problems and fields of engineering and look forward to future opportunities for collaboration in consulting, design and research.

To visit Itasca Consulting Group's website click here

For more information about Particle Fluid Code click here

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