The role of rock mass heterogeneity and buckling mechanisms in excavation performance in foliated ground at Westwood Mine, Quebec

Abstract

SynopsisOperations at Westwood mine in Quebec, Canada were temporarily halted in May 2015 after three largemagnitude seismic events occurred over two days. The mechanisms leading to these events, which caused severe damage to several accesses, were not well understood at first. This is partly due to the complex geology at the site, where massive, unaltered, strong, brittle, and seismically active rock can alternate with highly altered, weak, foliated, and buckling-prone rock at the metre scale. Other aspects of ground behaviour, such as the significant discrepancy in blast-hole performance between secondary and primary stopes and the propagation of damage from stopes to haulage drives in some locations, were also not well understood. In 2017, further geotechnical characterization of the rock mass was carried out and numerical back-analyses of several locations were completed using the continuum code FLAC3D. The objectives of the back analyses were to better understand the mechanisms controlling rock mass performance and to obtain a calibrated model for predictive stoping simulations. This paper presents the key aspects of the modelling, which include (1) an anisotropic rock mass strength model with properties derived from field and laboratory strength testing, and (2) a scheme to account implicitly for the deconfinement that accompanies buckling around excavations.

Development of rock mass strength block models at Cadia East mine

“…Test locations designated as disturbed are considered as an indicator of low point load index. The procedures, first applied to the study of rock strength variability at Niobec Mine in November of 2012 (Pierce 2014;Garza-Cruz & Pierce 2016) have since been applied to a number of orebodies, including Cadia East, Red Chris, Ghaghoo, Renard, Henderson, Eleonore, and Westwood (Bouzeran et al 2019). See Appendix for more detail on the procedure and data types collected.…”