Valley, Benoît

2014, Milkereit, Bernd, Saleh, Ramin, Huang, JW, Valley, Benoît

2011-10-26, Pun, Winnie, Saleh, Ramin, Zwaan, D., Milkereit, Bernd, Valley, Benoît, Pilz, Marco, Milkereit, Claus, Milkereit, R.

2012-12-1, Saleh, Ramin, Jeyaraj, R., Milkereit, Bernd, Liu, Q., Valley, Benoît

In an active underground mine there are many seismic activities taking place, such as seismic noises, blasts, tremors and microseismic events. In between the activities, the microseismic events are mainly used for monitoring purposes. The frequency content of microseismic events can be up to few KHz, which can result in wavelengths on the order of a few meters in hard rock environment. In an underground mine, considering the presence of both small wavelength and strong elastic contrasts, the simulation of seismic wave propagation is a challenge. With the recent availability of detailed 3D rock property models of mines, in addition to the development of efficient numerical techniques (such as Spectral Element Method (SEM)), and parallel computation facilities, a solution for such a problem is achievable. Most seismic wave scattering studies focus on large scales (>1 km) and weak elastic contrasts (velocity perturbations less than 10%). However, scattering in the presence of small-scale heterogeneities and large elastic contrasts is an area of ongoing research. In a mine environment, the presence of strong contrast discontinuities such as massive ore bodies, tunnels and infrastructure lead to discontinuities of displacement and/or stress tensor components, and have significant impact on the propagation of seismic waves. In order to obtain an accurate image of wave propagation in such a complex media, it is necessary to consider the presence of these discontinuities in numerical models. In this study, the effects of such a contrast are illustrated with 2D/3D modeling and compared with real broadband 3-component seismic data. The real broadband 3-component seismic data will be obtained in one of the Canadian underground mines in Ontario. One of the possible scenarios investigated in this study that may explain the observed complexity in seismic wavefield pattern in hard rock environments is the effect of near field displacements rather than far field. Considering the distribution of seismic sensors in a mine and the presence of seismic events within a mine, the recorded wavefield may represent a near-field displacement, which is not the case for most of seismic studies. The role of receiver characterization on the recorded event near the surface or around fault zones is also investigated. Using 2D/3D modeling, the effects of Vp/Vs variation on vertical and horizontal components of recorded amplitude has been shown.

2011, Pun, Winnie, Milkereit, Bernd, Valley, Benoît, Qian, Wei

As a proxy for stress in mines, passive monitoring from microseismics and active monitoring from controlled source resistivity survey may be utilized to better understand stress state changes. Repeated measurements over a continuous period of time are necessary to study any variations in the subsurface structure due to mining processes and natural events. The controlled source time-lapse surveys must be repeatable for meaningful studies such that any changes in the data are related to the earth?s response. This paper presents in-mine geophysical data from passive microseismics and active borehole-to-borehole resistivity surveys which show promising characteristics for stress monitoring.

2012-5-5, Valley, Benoît, Milkereit, Bernd, Pun, Winnie, Pilz, Marco, Hutchinson, Jean, Delaloye, Dani, Madjdabadi, Behrad M., Dusseault, Maurice, Thibodeau, Denis, Forsythe, Anneta, Hawkes, C., Kinakin, D., Proskin, S., Thibodeau, D.

Optimization of the mining sequence in terms of economics (maximizing net present value) often leads to multi-front mining methods generating pillars. Significant resources are tied up in these pillars, but mining them is often challenging. In order to improve our understanding of rock mass behaviour while extracting these pillars, an extensive monitoring program has been designed and implemented at Vale’s Coleman mine (Sudbury, Canada). The program focuses on existing and new technologies that have potential for monitoring deformation and rock mass property changes. It includes both active and passive methods: gravimeters, multi-point borehole extensometers, fiber optic strain meters, fixed and portable three-component seismic arrays, borehole imaging and sonic logging, and, repeated LiDAR surveys. This paper reports results from an initial project phase, when only a small amount of mining has taken place. The goal was to test and compare technologies in order to assess their sensitivity, accuracy, repeatability and suitability for underground mining conditions. Value is gained by having a broad range of monitoring devices running side by side, enabling comparisons and benchmarking.

2010, Valley, Benoît, Pun, Winnie, Milkereit, Bernd, Thibodeau, Denis

A key challenge for underground rock mechanics laboratories is to identify and develop the proper techniques to characterize rock mass changes and to monitor the processes under study. The International Fault Slip Control Research Initiative (IFSCRI), being led by the Centre for Excellence in Mining Innovation (CEMI), aimed at conducting underground experiments to improve our understanding of what controls induced and triggered seismicity. A preliminary project is dedicated to the development and testing of monitoring techniques that could potentially capture stress and strain field changes as well as characterize rock mass degradation processes (fracturing). A prerequisite to monitor rock mass change is to have techniques and methodologies available that present a high repeatability index when nothing changes. In this project, the rock mass changes of a 150m x 100m x 30m volume in a crown pillar will be monitored while it is being mined out. The stress, strain and rock mass changes induced will be captured by a dense borehole array, heavily equipped with various geophysical tools. The contemplated techniques include deformation measurement using multi-point borehole extensometers, micro-seismicity monitoring, noise and seismic tremor analyses, seismic tomography, borehole logging (televiewers, sonic logs and other physical properties logging), cross-hole DC/IP, an accelerometer network and strain measurement using optical fibers. This communication presents the experimental design process involving the anticipation of the rock mass response during mining. Initial data collection targets testing of the applicability of the proposed techniques and the evaluation of their repeatability index.