Seismic anisotropy in granite at the Underground Research Laboratory, Manitoba

Journal Article · Mon May 01 04:00:00 EDT 2000 · Geophysical Prospecting

DOI:https://doi.org/10.1046/j.1365-2478.2000.00195.x· OSTI ID:20076108

Holmes, G M; Crampin, S; Young, R P

The Shear-Wave Experiment 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 in situ anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any in situ shear-wave survey to date. Inversion of the shear-wave polarizations shows that the anisotropy of the in situ rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023{degree} and dip 35{degree}. The in situ anisotropy is probably due to microcracks with orientations governed by the in situ stress field and to mineral alignment within the weak gneissic layering. However, there is no unique interpretation as to the cause of the in situ 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 in situ 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.

• Research Organization: GeoScope Exploration Technologies, Inc., Calgary, Alberta (CA)
• OSTI ID: 20076108
• Journal Information: Geophysical Prospecting, Journal Name: Geophysical Prospecting Journal Issue: 3 Vol. 48; ISSN GPPRAR; ISSN 0016-8025
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
42 ENGINEERING
54 ENVIRONMENTAL SCIENCES
ANISOTROPY
EXCAVATION
GEOLOGIC FRACTURES
GRANITES
MANITOBA
ROCK MECHANICS
SEISMIC S WAVES
TUNNELS
UNDERGROUND DISPOSAL
UNDERGROUND MINING