Anelastic Strain Recovery and The Kaiser Effect Retention Span in the Carnmenellis Granite, U.K. |
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Authors: | S P Barr D P Hunt |
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Institution: | (1) Department of Mining Geology, WASM, Kalgoorlie, Australia, AU;(2) Camborne School of Mines, Exeter University, Cornwall, U.K., GB |
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Abstract: | Summary Knowledge of in-situ stress in rock masses is essential for mining and civil engineering design and the Kaiser effect method
of stress determination provides an economical alternative to currently applied investigation techniques. A practical problem
associated with this method is the loss of the Kaiser effect over time during the process of anelastic strain recovery, but
a direct relationship is observed between anelastic strain recovery and the number of acoustic emissions. The behaviour is
modelled here using the Kelvin and Burger rheological models, for the stages of creep during uniaxial laboratory loading,
anelastic strain recovery and the loss of the Kaiser effect, with constants being calculated and compared for samples loaded
under geological and laboratory conditions. It is found that the loss of the KE at low stress levels compares directly with
the process of anelastic strain recovery and fits the Burger model over the time scales of interest. A difference between
primary and secondary (undercored samples) recovery is demonstrated with a slower recovery for primary relaxation and with
samples taken from geological stress environments recovering more slowly than those loaded under laboratory conditions, for
all stress levels tested. |
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