Tensile damage behavior of water-saturated amphibolite at different clay contents: Bridging the micro and mesoscale

Understanding the tensile rupture behavior of rocks with varying clay contents is fundamental for assessing engineering stability. This study conducted Brazilian splitting tests on water-saturated amphibolite with different clay contents, investigating the microscopic fracture and damage characteristics using acoustic emission (AE), 3D laser scanning, and scanning electron microscopy (SEM) technologies. The evolution of microscopic damage and its correlation with macroscopic tensile strength characteristics were quantitatively analyzed. The influence mechanism of clay content on tensile mechanical properties was elucidated. The results indicated that varying clay contents resulted in contrasting trends in the splitting mechanical properties of water-saturated amphibolite. Specifically, the tensile mechanical parameters of water-saturated specimens with high clay content decreased, whereas those with low clay content increased. Compared to dry amphibolite, the densification of water-saturated specimens with low clay content was enhanced due to lower cumulative AE energy and a decrease in the fractal dimension of fracture surfaces. Conversely, the densification of water-saturated specimens with high clay content was diminished by higher cumulative AE energy and an increase in the fractal dimension of fracture surfaces, aligning with the observed changes in macroscopic mechanical properties. The process of water-rock interaction was categorized into three stages: clay mineral expansion, pore filling, and microcrack initiation. Water-saturated amphibolite with low clay content experienced the clay mineral expansion and pore-filling stages, while specimens with high clay content also underwent the microcrack initiation stage, which was the primary reason for the variability in tensile properties among water-saturated specimens with different clay contents.