Static and dynamic moduli of a weak sandstone

Abstract

Static moduli derived from the slope of a stress-strain curve and dynamic moduli derived from the velocity of elastic waves are significantly different for rocks, even though they should be equal according to the theory of linear elasticity. Proper knowledge about this difference might be useful because dynamic measurements are often the only information available about a rock. In tests on a dry sandstone, static and dynamic moduli are always different, except immediately after the direction of loading has been reversed. The results support the assumption that the difference between static and dynamic moduli can be ascribed to the difference in strain amplitude between static and dynamic measurements. At low stress levels, static and dynamic moduli increase with increasing stress during initial loading. In uniaxial compaction tests, the static compaction modulus decreases with increasing stress at higher stress levels, revealing a sensitivity to the location of the failure envelope. However, the corresponding dynamic modulus is totally insensitive to the failure envelope.