静水圧下における岩石の弾性定数および応力-歪み曲線について

抄録

Simultaneous measurements were made on longitudinal strain as well as velocities of P and S waves traveling through a rock specimen of granite under hydrostatic pressure up to 3.4 kilobars. When inelastic strain is defined by the difference of measured strain from linear stress-strain relation, it decreases nonlinearly with increase in applied pressure. The velocities of P and S waves drastically increase over lower pressure range because of nonlinear decrement of crack density pre-existing in the rock specimen. Two models of Dugdale-Barenblatt crack and circular crack were used to elucidate a possible mechanism of changes in crack density and inelastic strain. From a relation between crack density and inelastic strain for a composite material made of circular cracks and elastic matrix, it was found that average aspect ratio of cracks pre-existing in the rock specimen decreases with increase in applied pressure and is of the order of 10^-3. However, nonlinear decrement of crack density and inelastic strain cannot be sufficiently interpreted by use of the composite material containg only circular cracks. They are attributed to reduction of crack size in response to applied pressure. A composite material containing only Dugdale-Barenblatt cracks makes it possible reasonably to explain the measured results. The cohesive force introduced in Dugdale-Barenblatt crack model plays an important role for crack size to vary in response to hydrostatic pressure. The cohesive force was estimated from analysis of the measured results to be 1.8 kilobars.