Effects of inhomogeneity and statistical and material anisotropy on THM simulations

When modeling the material properties of host rocks for thermo-hydro-mechanical simulations in barrier integrity investigations for deep geological disposal of radioactive waste, numerous modeling aspects must be considered. If complete information were available, the material properties would be functions of space, with inhomogeneity and anisotropy expressed by spatially varying and tensor-valued coefficients. In practice, uncertainty is present in particular related to spatial variability of physical properties. This variability can be modeled by random fields, whose realizations are functions of space. A common choice is a Gaussian random field, determined by its mean and two-point covariance function. Anisotropy can occur both in the statistical covariance structure, resulting in different correlation lengths along principal axes, and in the physical properties themselves, leading to tensor-valued random fields. In this study, we focus on both cases, considering dominant material properties such as thermal conductivity, intrinsic permeability, and Young’s modulus, and present numerical simulations illustrating the effects of inhomogeneity, randomness, and anisotropy. Since spatial variability is a key feature in the analysis of in-situ data, this study quantifies the individual contribution of each of the listed effects in a well-controlled synthetic case and discusses them in the context of scale.