In the framework of a deep geological radioactive waste disposal in France, the hydromechanical properties of the designated host rock, the Callovo-Oxfordian claystone (COx), are investigated in laboratory tests. Experiments presented in this study are carried out to determine several coefficients required within a transversely isotropic material model. They include isotropic compression tests, pore pressure tests, and deviatoric loading tests parallel and perpendicular to the bedding plane. We emphasize the adapted experimental devices and testing procedures, necessary to detect small strains under high pressures, on a material, which is sensitive to water and has a very low permeability. In particular, we discovered a significant decrease of elastic stiffness with decreasing effective stress, which was observed to be reversible. In both isotropic and deviatoric tests, a notable anisotropic strain response was found. The Young modulus parallel to bedding was about 1.8 times higher than the one perpendicular to the bedding plane. A notably low Poisson ratio perpendicular to the bedding plane with values between 0.1 and 0.2 was evidenced. While the anisotropy of the back-calculated Biot coefficient was found to be low, a significant anisotropy of the Skempton’s coefficient was computed. The performed experiments provide an overdetermined set of material parameters at different stress levels. Using all determined parameters in a least square error regression scheme, seven independent elastic coefficients and their effective stress dependency are characterized. Parameters measured under isotropic loading are well represented by this set of coefficients, while the poroelastic framework with isotropic stress dependency is not sufficient to describe laboratory findings from triaxial loading.

中文翻译：

---

Callovo-Oxfordian 粘土的横向各向同性多孔弹性行为：一组与应力相关的参数

在法国深部地质放射性废物处置的框架内，在实验室测试中研究了指定寄主岩石 Callovo-Oxfordian 粘土岩 (COx) 的流体力学特性。本研究中提出的实验用于确定横向各向同性材料模型中所需的几个系数。它们包括平行和垂直于层理平面的各向同性压缩试验、孔隙压力试验和偏载试验。我们强调在对水敏感且渗透性非常低的材料上检测高压下的小应变所必需的适应性实验设备和测试程序。特别是，我们发现随着有效应力的降低，弹性刚度显着降低，这被观察到是可逆的。在各向同性和偏心测试中，都发现了显着的各向异性应变响应。平行于层理的杨氏模量比垂直于层理平面的杨氏模量高约 1.8 倍。证明垂直于层理平面的泊松比非常低，值在 0.1 和 0.2 之间。虽然发现反向计算的 Biot 系数的各向异性很低，但计算了 Skempton 系数的显着各向异性。所进行的实验提供了一组不同应力水平下的超定材料参数。使用最小二乘误差回归方案中的所有确定参数，表征七个独立的弹性系数及其有效应力依赖性。在各向同性载荷下测得的参数由这组系数很好地表示，