花こう岩の圧縮強度と変形特性に及ぼすひずみ速度の影響

Abstract

Triaxial compression tests at 50 MPa confining pressure and room temperature have been conducted under various constant axial strain rates ranging between 10-7 s-1 and 10-3 s-1 by using dried specimens of Inada granite. The experimental results showed that the ultimate strength, axial strain at failure, Poisson's ratio and anelastic energy which may be considered as the energy required to generate new cracks or to propagate pre-existing cracks in the compression process, increased with increasing strain rate. In addition, Young's modulus and fracture angle which is the angle contained by fracture plane and lateral section of specimen, decreased with increasing strain rate.By comparing the strain rate dependence of the compressive strength and elastic constants of granites determined experimentally in the present study and the previous works, it can be decided that the strain rate dependence of the different rocks showed different features although the rocks were same granites in petrologic classification. First, the compressive strength increased linearly as the logarithm of the strain rate increase at intermediate strain rate range (considered as from 10-8 s-1 to 10-1 s-1, approximately) in any granite. At high confining pressure, the strain rate dependence of the strength is enhanced in fine-grained granites; in contrast, the dependence is enfeebled in medium-grained granites. Secondly, the strain rate dependence of Young's modulus had more complex behaviors than that of the strength. At the intermediate strain rate range, there are three types of granites which were (1) their Young's modulus did not depend on the strain rate, (2) their modulus increased with the increase of the strain rate, and (3) their modulus decreased with the increase.