UNSPECIFIED (1993) ULTRASONIC-IMAGING AND ACOUSTIC-EMISSION MONITORING OF THERMALLY-INDUCED MICROCRACKS IN LAC-DU-BONNET-GRANITE. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 98 (B12). pp. 22231-22243. ISSN 0148-0227

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Abstract

Concurrent ultrasonic tomography and acoustic emission monitoring were employed to study thermally induced microfracturing in an unconfined, 15-cm cube of Lac du Bonnet granite from Atomic Energy of Canada Limited's Underground Research Laboratory. An electrical resistance cartridge heater, placed in a central vertical borehole, was used to cycle the sample to progressively higher peak temperatures between 75-degrees-C and 175-degrees-C. Tomography data were collected, at room temperature, before and after each thermal cycle. Acoustic emission monitoring proceeded during both heating and cooling phases of each thermal cycle. Microfractures opened above 80-degrees-C and eventually coalesced into a macroscopic fracture plane. The macroscopic fracture originated at the outer edges of the sample and then extended inward, parallel to the fast velocity direction, and eventually intersected the borehole. Both acoustic emission locations and slowness difference tomography clearly delineated the fracture plane. We attribute the development of the macroscopic fracture to a thermal gradient cracking mechanism acting upon a brittle, anisotropic medium.

Item Type:	Journal Article
Subjects:	Q Science > QE Geology
Journal or Publication Title:	JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Publisher:	AMER GEOPHYSICAL UNION
ISSN:	0148-0227
Date:	10 December 1993
Volume:	98
Number:	B12
Number of Pages:	13
Page Range:	pp. 22231-22243
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/20929

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