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October 15-17, 2018
The Australian Centre for Geomechanics looks forward to hosting the Fourth International Symposium on Block and Sublevel Caving in Vancouver in October 2018. This follows previous symposia held in Santiago in 2014; Perth, 2010 and Cape Town, 2007.
The growing popularity of caving methods around the world is largely due to the very low production cost and the intrinsic safety associated with the mining approach. It is often the only viable mining method for some of the lower grade massive orebodies that are becoming too deep for open pit mining. Cave mining has become one of the most research intensive areas of mining engineering in recent times. Mining companies need to be kept informed of the latest technological developments from caving research, and researchers require a regular platform to present their results and interact with industry practitioners.
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DAY 1, SESSION 3: CAVE MECHANICS AND NUMERICAL MODELLING
Three-dimensional simulation of cave initiation, propagation and surface subsidence using a coupled finite difference - cellular automata solution Y Hebert, G Sharrock, Itasca Australia Pty Ltd, Australia
ABSTRACT: This paper outlines a new methodology for modelling caveability and subsidence using bi‐directional coupling between the continuum code FLAC3D and the Cellular Automata code CAVESIM. FLAC3D, using the CaveHoek constitutive model, simulates the progressive failure and disintegration of the rock mass from an intact/jointed to a caved material. CAVESIM simulates gravity flow, in particular the collapse, bulking and movement of caved rock. The coupled method captures many important aspects of caveability affecting cave design such as hang‐up formation, material recovery, timing of surface breakthrough or interaction with other lifts, crater development and surface subsidence. The key to improved modelling of many of these aspects is the ability to accurately capture the impact of draw and gravity flow on cave propagation and subsidence.
Numerical simulations of a centrifuge model of caving D Cumming-Potvin, J Wesseoo, Australian Centre for Geomechanics and The University of Western Australia, Australia; M Pierce, Pierce Engineering, USA; T Garza-Cruz, L Bouzeran, Itasca Consulting Group, USA; SW Jacobsz, E Kearsley, University of Pretoria, South Africa
ABSTRACT: Validation and calibration of numerical models is vitally important, particularly in the field of cave mining where our ability to monitor the caving rock mass is limited. As part of a project investigating caving mechanics, physical models of caving were tested in a geotechnical centrifuge (Cumming-Potvin et al. 2016b). This paper describes numerical simulations of one of the centrifuge tests. Two approaches were used, so the relative strengths and weaknesses could be compared. The Itasca caving algorithm approach was implemented in FLAC3D and a bonded block model (BBM) approach implemented in 3DEC. The results showed that there was a good match with the physical model in some respects. Both numerical approaches were able to capture the discontinuity in the damage profile seen in the physical model, and the shape of the failed zones also matched the physical model well.
The match appeared to be better for the BBM approach. There is some uncertainty as to whether the mechanism of failure seen in the physical model was exhibited in the numerical models. The match between the numerical and physical models could have been improved via further calibration. However, this was outside the scope of this study. Overall, the results show that the numerical approaches used are suitable for practical use in the modelling of caving, particularly if they are suitably calibrated and/or validated using in situ monitoring data.
DAY 3, KEYNOTE ADDRESS & SESSION 11: DRAW CONTROL/FRAGMENTATION (2)
ABSTRACT: The hybrid REBOP-FLAC3D approach allows prediction of the limits of the geomechanical zones defining the cave as a function of production. The results of the model can be used to derive estimates of: 1) caveability and caving rate; 2) abutment stresses and cave loads; 3) recovery and dilution entry; 4) fragmentation and 5) breakthrough timing and subsidence.
The approach simulates the caving process by explicitly modelling each isolated movement zone derived from REBOP into FLAC3D to determine the yielded zone and cave back associated with mass drawn. After one cycle of extraction, REBOP informs the location of the movement zones and the presence of air (if it exists) to the continuum FLAC3D model. FLAC3D solves stresses associated with the presence of these zones and estimates the yielded zone surrounding the cave. FLAC3D informs REBOP which zones (initially inactive) could now be mobilized. The procedure is repeated until the draw schedule used as an input in REBOP is finished.
Two of the main advantages of the hybrid approach include the capability of studying the potential impacts of isolated draw on cave growth and point loading on the extraction level as well as the effect of including explicitly the air gap and mechanisms of fines migration and rilling on cave growth and subsidence. Two case studies are presented showing the capabilities of the hybrid approach.
SESSION 13: SUBSIDENCE AND MONITORING
lnSAR as a practical tool to monitor and understand large-scale mining-induced ground deformations in a caving environment K Makitaavola, BM Stockel, TSavilahti, Luossavaara-Kiirunavaara Aktiebolag (LKAB), Sweden; J Sjoberg, Itasca Consultants AB, Sweden; J Dudley, MA McParland, R Morin, MDA Geospatial Services, Canada
ABSTRACT: The application of InSAR technology to monitor mining-induced deformations has been successfully applied at the Kiruna mine site for more than seven years. Ground deformations are caused by the use of large-scale sublevel cave mining to extract iron ore from the underground Kiirunavaara Mine. More recently, InSAR monitoring has also been applied at the nearby LKAB Malmberget mine site, also mined using sublevel caving. In both cases, the induced ground deformations are affecting existing infrastructure, necessitating an "urban transformation" process to relocate surface infrastructure and/or residential areas. Control and follow-up of ground deformations has thus become vital, and InSAR monitoring has proven to play an ever-increasing important role in this. The technique and its use at a high-latitude (snow-covered) site, and for LKAB's specific purposes, was initially investigated and verified during a five-year research project. A slightly expanded monitoring program is now in place in Kiruna, which supplements the standard GPS-monitoring. At Malmberget, InSAR monitoring has enabled verification of the overall movement trends with respect to major shear structures in the area. Additionally, increased reliability in areas with poor GPS coverage has been achieved, as well as increased data coverage in periods between GPS-measurement campaigns. Combined use of InSAR and GPS data has also helped to calibrate and constrain numerical models, as exemplified in this paper. Work is now on-going to implement the use of InSAR to monitor the criterion for allowable ground deformations at both sites, as well as in integrated interpretation of caving mechanics and deformations.
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