Evolution of Soil Fabrics toward Critical State for Granular Soils: A Comprehensive Investigation

The critical-state theory (CST) serves as the foundation of modern soil mechanics and has gained widespread acceptance for explaining the behavior of granular materials. The classical CST does not address the fabric anisotropy of granular materials, leading to questions about the uniqueness of the critical state when considering such anisotropy. Recently, the development of anisotropic critical-state theory (ACST) highlights that fabric anisotropy of granular materials should reach a unique normalized value at the critical state. However, ACST does not specify which fabric tensor is used to characterize the microstructure of soils. In this study, we present a comprehensive characterization of various soil fabrics, including contact-based fabric tensor, void-based fabric tensor, and particle-void fabric, respectively. We employ three-dimensional clumped particles to approximate different shapes of Toyoura sand particles, which makes the characterization of soil fabric more accurate. Discrete element method simulations of conventional triaxial compression tests under both drained and undrained conditions are conducted on soil samples with different initial confining pressures and void ratios. The evolution of various fabrics toward the critical state is compared and discussed. Moreover, we establish relationships among contact-based fabric, void-based fabric, particle-void fabric, mean effective stress, and void ratio at the critical state. The study provides new insights into understanding the relations between the critical state and the microstructure of granular soils.