Ford, NT, Silverton, TR & Cottrell, MG 2008, 'Rock Mass Characterisation of a Prospective Base Metal Deposit Using a Combined FracMan/ELFEN Approach', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium
, Australian Centre for Geomechanics, Perth, pp. 605-617.
This paper demonstrates how the combined use of a discrete fracture network tool (FracMan) and a combined continuum-discrete element tool (ELFEN) has resulted in significant improvements in the understanding of the fundamental mechanisms contributing to rock mass behaviour in poor ground allowing geotechnical risks to be better understood and managed.
The Golder Associates’ FracMan combined with Rockfield Software’s ELFEN code has been applied to the problem of quantifying the geotechnical risk for a number of potential mining methods being considered for the recovery of a selected lead/zinc ore body in Algeria.
FracMan enables the generation of a rock mass model based on geotechnical data obtained from boreholes, photographs and face mapping. It then permits the creation of integrated three-dimensional (3D) stochastic models using a discrete fracture network (DFN) description. The synthetic fractures in a DFN model can have any size and shape, and can be located deterministically, stochastically, or conditioned to field measurements. The stability of excavations (both 3D benched slopes and complex underground shapes) can be analysed using FracMan. This allows for the identification of completely defined rock blocks formed by finite fractures and allows for the factor of safety of these blocks to be determined in both supported and unsupported ground. The underlying Monte Carlo technique enables sensitivities to ground variability and the quantification of the geotechnical risk for an excavation to be determined.
A FracMan model of the selected rock mass from a lead/zinc deposit in poor ground was created using the available geotechnical data. The resulting DFN formed the basis of a series of conceptual models, analysed using the combined continuum-discrete element capabilities of ELFEN. Various potential excavation shapes for underground mining were considered to assess the viability of the mining method and quantify the associated geotechnical risk. ELFEN has been used to examine the fundamental mechanisms contributing to rock fragmentation and the consequent flow of material, this approach enables the rock mass performance to be predicted with confidence.
The use of FracMan modelling and ELFEN to determine the geotechnical risk is a relatively new approach and provides a more powerful tool than traditional methods of rock mass assessment, allowing greater confidence in calculating geotechnical risk during the process of mining method selection and design.
Baecher, G.B., Einstein, H.H. and Lanney, N.A. (1977) Statistical description of rock properties and sampling. Proceedings 18th U.S. Symposium on Rock Mechanics, Barton, C.M., Colorado School of Mines Press Colorado, pp. 1–8.
Chitombo, G. (2005) The International Caving Study (ICS) End of project report. ICS II. JKMRC, The University of Brisbane, Queensland, Australia.
Collins, T. (2004) Image J: Image Processing and Analysis In Java. Toronto: Wright Cell Imaging Facility, Toronto Western Research Institute.
Cottrell, M.G. (2002) Rational Computational Strategies for Modelling High Velocity Impact, PhD thesis, University of Wales Swansea.
Curran, J. (2006) Unwedge v.3.0 Tutorial Manual. Rocscience.
Dershowitz, W., Lee, G., Geier, J., Foxford, T., LaPointe, P. and Thomas, A. (2004) Fracman, Interactive Discrete Feature Data Analysis, Geometric Modelling, and Exploration Simulation, User Documentation, Golder Associates Inc, 231 p.
Elmo, D., Vyazmensky, A., Stead, D. and Rance, J.R. (2007) A Hybrid FEM/DEM Approach To Model The Interaction Between Open Pit And Underground Block Caving Mining. Proceedings 1st Canada–U.S. Rock Mechanics Symposium. Vancouver B.C. 27–31 May 2007.
Goodman, R. and Shi, G. (1985) Block Theory and Its Application to Rock Engineering, Prentice–Hall, London.
Hoek, E. (2000) Practical Rock Engineering. Rocscience.
Hoek, E., Carranza, T.C. and Corkum, B. (2002) Hoek–Brown Failure Criterion – 2002 Edition. Proceedings of the Fifth North American Rock Mechanics Symposium, Toronto, Canada Vol. 1, pp. 267–273.
Klerck, P.A. (2000) The finite element modelling of discrete fracture in quasi brittle materials. PhD thesis, University of Wales Swansea.
Klerck, P.A., Sellers, E.J. and Owen, D.R.J. (2004) Discrete fracture in quasi brittle materials under compressive and tensile stress states, Computer Methods in Applied Mechanics in Engineering, Vol. 193, pp. 3035–3056.
Mandelbrot, B.B. (1985) Self-Affine Fractals and Fractal Dimension, Physica Scripta, 32 p, pp. 257–260.
Mathews, K.E., Hoek, E., Wyllie, D.C. and Steward, S.B.V. (1980) Prediction of Stable Excavations for Mining at Depths Below 1000 Metres in Hard Rock. CANMET 802–1571.
Owen, D.R.J., Feng, Y.T., de Souza Neto, E.A., Cottrell, M.G., Wang, F., Pires, F.M. and Yu, J. (2004) The Modelling Of Multi-Fracturing Solids And Particulate Media, International Journal of Numerical Methods in Engineering, Vol. 60, pp. 317–339.
Pine, R.J., Coggan, J.S., Flynn, Z. and Elmo, D. (2006) The Development of A Comprehensive Numerical Modelling Approach For Pre-Fractured Rock Masses. Rock Mechanics and Rock Engineering, 39, 5, pp. 395–419.
Rance, J.M., Van As, A., Owen, D.R.J., Feng, Y.T. and Pine, R.J. (2007) Computational Modelling Of Multiple Fragmentation In Rock Masses With Application To Block Caving. Proceedings 1st Canada–US Rock Mechanics Symposium, Vancouver, Canada.
Rockfield (2008) ELFEN Finite Element/Discrete Element code. Rockfield Software Ltd, Swansea.
Trueman, R., Mikula, P., Mawdesley, C. and Harries, N. (2000) Experience In Australia With The Application Of The Mathews' Method For Open Stope Design, Canadian Institute of Mining Bulletin 93, pp. 162–167.
Vyazmensky, A., Elmo, D., Stead, D. and Rance, J.R. (2007) Combined Finite-Discrete Element Modelling Of Surface Subsidence Associated With Block Caving Mining. Proceedings 1st Canada–U.S. Rock Mechanics Symposium. Vancouver, Vol. 1, pp. 467–475.
Yu, J. (1999) A contact interaction framework for numerical simulation of multi-body problems and aspects of damage and fracture for brittle materials. PhD thesis, University of Wales Swansea.
Zhang, L. and Einstein, H.H. (1998) Estimating The Mean Trace Length Of Rock Discontinuities. Rock Mechanics and Rock Engineering, 4, Springer, pp. 217–235.
Zhang, L. and Einstein, H.H. (2000) Estimating the Intensity of Rock Discontinuities. International Journal of Rock Mechanics and Mining Science, 37, Elsevier, pp. 819–837.
Zhang, L., Einstein, H.H. and Dershowitz, W.S. (2002) Stereological Relationship Between Trace Length And Size Distribution Of Elliptical Discontinuities. Géotechnique, 52, Institute of Civil Engineers, pp. 419–433.