Development of artificial sill pillar design, Lupin Mine, Northwest Territories, part 2: pre-mining ground stress determinations

Abstract

The Echo Bay Mines Ltd. Lupin operation in Northwest Territories produces gold from a steeply dipping orebody by sub-level longhole open stope mining, leaving sill pillars in the ore. To increase ore recovery, a joint research project has been established to design and develop guidelines for artificial sill pillars. To provide background information for stability evaluations, pre-mining ground stress determinations were conducted on the 410 m and 890 m levels of the mine. Ground stress determination from overcoring strain relief measurements indicates that, generally, the maximum principal compressive stress is horizontal in a NE/SW direction, and the intermediate principal compressive stress is sub-horizontal prevailing in a NW/SE direction. The minimum principal compressive stress is sub-vertical with varying direction. Stress gradients for maximum, intermediate and minimum principal compressive stresses vary, ranging from 0.0430 to 0.0693 MPa/m, 0.0271 to 0.0505 MPa/m, and 0.0127 to 0.0397 MPa/m, respectively. A comparison of average stress gradients, however, suggests that the Lupin Mine data follow the trend established from underground stress determinations in the Canadian Shield.