岩石のクラスＩＩ特性に関する一考察

Abstract

The class II behavior was investigated by both numerical simulations and experiments, and the following results were obtained.Firstly, class II behavior was presented by a spring model which consists of two tandem connected sheaves of springs with different strength, which is assumed to follow the Gaussian distribution. In the pre-failure region, spring elements fail similarly between the two sheaves, but failure concentrates on one of them after the strength failure point. And the smaller the coefficient of variation of strength, the severer the concentration of failure. Such a mechanism, that is to say, failure concentration may lead to the class II behavior as Hudson [17] has illustrated with simple diagram.The FEM stochastic model also showed that smaller coefficient of variation of strength leads to class II behavior, much similar to the result obtained from the spring model. And the FEM stochastic model also showed that end-boundary condition and/or hight-to-width ratio have little influence on the shape of stress-strain curve.Secondly, experiments showed that stress vs. recoverable-strain curves of the all tested rock samples have a positive slope in the post-failure region, under either uniaxial or triaxial compression. And it is found that an important difference between class I and class II behaviors is the difference of permanent deformation.So class I rock samples have large permanent deformation and class II rock samples have small one.Because numerical models used in this study considered only elastic deformation, they can only give an excellent approximation to the behavior of such rock which shows class II characteristics and has a minor permanent deformation.