Abstract

Sedimentary rocks often shows anisotropic deformation behaviors owing to sedimentary structures. It is significantly important to correctly determine deformation anisotropy (principal orientation and elastic parameters of anisotropy) for the construction and disaster prevention of rock structures. In this study, three consolidated-drained triaxial tests of Japanese mudstones are conducted with measuring six full strain tensor, and the deformation anisotropy in each specimen is detected. The results demonstrated as follows; Strain tensor responses during triaxial compression shows non-co-axial stress-strain behaviors. The anisotropic behaviors are occurred owing to the bedding orientation because the principal orientation almost agrees with bedding orientation of mudstone. The transversely isotropic elastic parameters of mudstone are also determined by using the full strain responses. The ratio of the Young’s modulus of bedding plane to that of the perpendicular orientation shows the values of 0.55–2.83.

1 Introduction

Deformation properties of rocks must be correctly determined for reasonable construction of rock structures; e.g., tunnels, rock foundations and so on. Rocks often show anisotropic deformation behaviors due to the sedimentary structure. Deformation anisotropy of sedimentary rocks have been studied for a long time (e.g., Hayano et al. 1999), and those studies usually assumed the principal orientation of anisotropy to agrees with the vertical orientation. However, in a geologically active area like Japan, sedimentary layers were often bent and folded by crustal movements, and then, the vertical orientation may not be agreed with the sedimentary structures (bedding plane). To evaluate correct deformation properties of sedimentary rocks, both principal orientation of anisotropy and the anisotropic elastic parameters (deformation anisotropy) should be determined. Furthermore, such anisotropic rocks show non-axisymmetric deformation behaviors in laboratory triaxial test, and the behaviors are changed owing to bedding orientation (Togashi et al. 2018a). Then, we proposed methods of determining deformation anisotropy by a single laboratory test by measuring such non-axisymmetric strain tensor response (Togashi et al. 2017, Togashi et al. 2018b).

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