1887
Volume 48 Number 3
  • E-ISSN: 1365-2478

Abstract

The at Atomic Energy of Canada Limited's Underground Research Laboratory was probably the first controlled‐source shear‐wave survey in a mine environment. Taking place in conjunction with the excavation of the Mine‐by test tunnel at 420 m depth, the shear‐wave experiment was designed to measure the anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any shear‐wave survey to date. Inversion of the shear‐wave polarizations shows that the anisotropy of the rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023° and dip 35°. The anisotropy is probably due to microcracks with orientations governed by the stress field and to mineral alignment within the weak gneissic layering. However, there is no unique interpretation as to the cause of the anisotropy as the fabric orientation agrees approximately with both the orientation expected from extensive‐dilatancy anisotropy and that of the gneissic layering. Eight raypaths with shear waves propagating wholly or almost wholly through granodiorite, rather than granite, do not show the expected shear‐wave splitting and indicate a lower anisotropy, which may be due to the finer grain size and/or the absence of gneissic layering within the granodiorite. These results suggest that shear waves may be used to determine crack and mineral orientations and for remote monitoring of a rockmass. This has potential applications in mining and waste monitoring.

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2001-12-24
2024-03-29
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