Fault growth and acoustic emissions in confined granite

Applied Mechanics Reviews
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Abstract

The failure process in a brittle granite was studied by using acoustic emission techniques to obtain three dimensional locations of the microfracturing events. During a creep experiment the nucleation of faulting coincided with the onset of tertiary creep, but the development of the fault could not be followed because the failure occurred catastrophically. A technique has been developed that enables the failure process to be stabilized by controlling the axial stress to maintain a constant acoustic emission rate. As a result the post-failure stress-strain curve has been followed quasi-statically, extending to hours the fault growth process that normally would occur violently in a fraction of a second. The results from the rate-controlled experiments show that the fault plane nucleated at a point on the sample surface after the stress-strain curve reached its peak. Before nucleation, the microcrack growth was distributed throughout the sample. The fault plane then grew outward from the nucleation site and was accompanied by a gradual drop in stress. Acoustic emission locations showed that the fault propagated as a fracture front (process zone) with dimensions of 1 to 3 cm. As the fracture front passed by a given fixed point on the fault plane, the subsequent acoustic emission would drop. When growth was allowed to progress until the fault bisected the sample, the stress dropped to the frictional strength. These observations are in accord with the behavior predicted by Rudnicki and Rice's bifurcation analysis but conflict with experiments used to infer that shear localization would occur in brittle rock while the material is still hardening.
Publication type Article
Publication Subtype Journal Article
Title Fault growth and acoustic emissions in confined granite
Series title Applied Mechanics Reviews
DOI 10.1115/1.3121387
Volume 45
Issue 3S
Year Published 1992
Language English
Publisher American Society of Mechanical Engineers
Contributing office(s) Earthquake Science Center
Description 9 p.
First page S165
Last page S173
Conference Title Symposium on Material Instabilities in conjunction with the 22nd Midwestern Mechanics Conference
Conference Location Rolla, MS
Conference Date Oct 1, 1991
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