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Determination of viscosity of rocks by a dynamic resonance technique Janakiraman, Coimbatore Subrahmanyam

Abstract

Results of forced vibration tests in longitudinal and transverse modes on three different rocks are presented. The experimental investigation leads to evaluation of solid viscosity parameters as a function of frequency and logarithmic decrement. Linear viscoelasticity theory is applied to the test results within the frequency range studied. The test results indicate that the rheological parameter viscosity of the rocks tested, quartzite, granodiorite and an argilite, is of the order of 10⁸ to 10⁹ poises. Methods of predicting solid viscosity parameters from forced vibration resonance tests by linear viscoelastic theories are derived. The correspondence principle, which is based on the solution to steady state sinusoidal oscillation is not strictly applicable, but does yield results which are of the same order as the measured relationships. The behaviour of rocks to idealized rheological models has been examined. Measurements of the viscosity and complex moduli are described and from a consideration of the results obtained the type of mechanical model most respresentative of the behaviour of rocks is suggested. A method for predicting directional properties of rocks using photo-elastic studies for different loading conditions is examined. This enables allowances to be made for the wide variation in dynamic test results on rocks. However, it is felt that the dynamic method of determining viscosity may have more application in the examination of rock structure, since a comparison of the laboratory and field test results at the same temperature and pressure yields a method for structural design involving rocks.

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