Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression |
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Authors: | Florian Amann Edward Alan Button Keith Frederick Evans Valentin Samuel Gischig Manfred Blümel |
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Institution: | (1) Engineering Geology, Institute of Geology, Swiss Federal Institute of Technology, Sonneggstrasse 5, 8092 Zurich, Switzerland;(2) Geoconsult, Pvt. Ltd, Plot 473, Industrial Estate, Udyog Vihar, Sector 19, Phase V, Gurgaon, India;(3) Institute for Rock Mechanics and Tunnelling, Graz University of Technology, Rechbauerstrasse 12, 8010 Graz, Austria |
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Abstract: | The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal,
underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France)
in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes
combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered
from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing
servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal
to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation
and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold
occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress–strain
behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress. |
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