A LABORATORY INVESTIGATION INTO THE ELASTIC PROPERTIES OF LIMESTONES*

Abstract

AbstractMeasurements have been made by the resonance method of the longitudinal bar velocities and the transverse velocities of 29 chemically pure limestones of varying porosity. The elastic anisotropy factors of the limestones were found to vary over a wide range. For the isotropic limestones, both the longitudinal and the transverse velocity decrease in general with increasing porosity, but this decrease is somewhat irregular. The irregularities in the velocity were found to correlate with the irregularities in the electrical resistivity of the samples when saturated with a standard salt solution, and with those in their tensile strength. This correlation indicates an influence on the velocity of the geometry of the pore space of the rock and of its counterpart: the geometry of the matrix. Indications have been obtained that a condition akin to weathering may be partly responsible for the irregularities in the velocities.Saturating the samples with water was found to result in a decrease of their velocities. An investigation of the available literature, combined with measurements made in our laboratory with a low frequency pulse method, indicate that water saturation results in a decrease of the velocity at low frequencies and in an increase of the velocity at high frequencies.Since other investigators have shown that the velocities of dry rock are hardly effected by the frequency, one must conclude that the velocities of water saturated rock do change appreciably with frequency.The values of Poisson's ratio were found to decrease with increasing porosity, but more so for the dry samples than for the water saturated samples. A possible explanation is that the cross‐contraction and cross‐dilatation is partly consumed in changing the diameters of the pores, thus reducing the effect on the outer diameter of the sample; this mechanism would be partly resisted by water filling the pores.