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Cylinders of Barre and Westerly granites have been compressed to failure in static fatigue tests under dry and wet conditions at 1 Kb confining pressure and temperatures of 24 ø and 200øC. The effect of increasing temperature and water content is, as expected, to weaken the rocks appreciably and to reduce the time to failure, at constant stress, by about two orders of magnitude. The activation energy estimated for dry Barre granite deformed in the temperature range 24 • to 200•C is 10.2 Kcal/mol which seems reasonable and is consistent with other work at higher temperatures. Extrapolation of the static fatique equations obtained for specimens deformed at 200•C, both wet and dry, to 108 years yields maximum stress differences near 3 Kb. While such extrapolations may be reasonable for intact material over time-spans of interest to national concerns, the stresses obtained seem unreasonably high for tectonic deformations. The discrepancy probably results from the very short durations of the tests which do not permit effective operation, at these low temperatures, of the several thermally-activated weakening effects of H20 on silicates.

No abstract