Multiscale interactions of elastic anisotropy in unsaturated clayey rocks using a homogenization model

• Published in: Acta geotechnica 2023-05, Vol.18 (5), p.2289-2307
• Main Authors: Ip, Sabrina C. Y., Borja, Ronaldo I.
• Format: Article
• Language: English
• Subjects: Anisotropy; Clay; Clay minerals; Complex Fluids and Microfluidics; Elastic anisotropy; Elastic properties; Elasticity; Engineering; Evolution; Foundations; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Homogenization; Hydraulics; Mechanical properties; Microstructure; Research Paper; Rock; Rocks; Saturation; Soft and Granular Matter; Soil Science & Conservation; Solid Mechanics; Stiffness
• ISSN: 1861-1125; 1861-1133
• DOI: 10.1007/s11440-022-01784-2

The microstructure of a geomaterial plays a significant role in determining its macroscale properties. Most clay rocks have an anisotropic microstructure due to preferential orientation of the pores and mineral grains, which results in transversely isotropic mechanical properties. Their anisotropic microstructure is complex and spans multiple orders of magnitudes. The interactions between anisotropy at different scales in these rocks can give rise to emerging properties such as saturation-dependent elastic anisotropy. In this study, we develop a homogenization model with three levels of upscaling to capture the multiscale interactions of elastic anisotropy in unsaturated clay rocks. The model provides an enriched description of the elastic behavior of clay rocks during changes in the degree of saturation by bridging the nano-, micro- and macroscale microstructures. Stress-point simulations are presented to demonstrate the interactions between anisotropy at different spatial scales that result in the elastic behavior of clay rocks observed in the literature, including constant anisotropy, evolving anisotropy and a rotation of the principal orientation of anisotropy. The results highlight that constant and evolving elastic anisotropy can originate from the same microstructural features that either neutralize or enhance one another. Overall, the proposed model offers a quantitative link between anisotropy at multiple scales in clay rocks and its macroscopic anisotropic stiffness.