Subjects: Mine Engineering Technology >> Mine Geology submitted time 2025-07-17
Abstract： Clay minerals, primarily including kaolinite, chlorite, illite, and montmorillonite, are widely distributed in fault zones. These minerals are characterized by small particle size, large specific surface area, and a strong tendency to adsorb water and cations. Their hydration and swelling behavior causes volume expansion upon water absorption, forming water films that act as lubricants and reduce the friction coefficient. Additionally, clay minerals exhibit low friction coefficients, low healing rates, and velocity-strengthening behavior. These combined properties significantly affect the strength and slip stability of granite faults. The South China region, located in the middle of the South China Block within the Mesozoic Eurasian tectono-magmatic belt and spanning the Yangtze and Cathaysian plates, has experienced intense tectonic activity due to plate subduction, resulting in the widespread formation of granite. This study focuses on the interaction mechanisms between granite faults and clay minerals. While the effects of individual clay minerals on the frictional properties of granite faults have been extensively studied, the coupled influence of multiple clay minerals on the friction coefficient and velocity dependence remains unclear. Therefore, this study investigates the combined effects of multiple alteration minerals on the frictional behavior and velocity dependence of granite fault gouge.In this research, three clay minerals—montmorillonite, chlorite, and kaolinite—were mixed in binary combinations (1:1) and as a ternary mixture (1:1:1). These mixtures were then blended with granite powder in specific proportions to prepare experimental samples. Under a constant normal stress of 20 MPa and a constant water content of 5%, velocity-stepping and healing experiments were conducted using a direct shear apparatus, accompanied by acoustic emission (AE) monitoring to track microcrack development. The velocity dependence parameters and healing behavior of the samples were observed, and post-experiment scanning electron microscopy (SEM) was used to examine their microstructures.The results indicate that, unlike intact granite where tensile cracks dominate, fault gouge exhibits prominent shear fractures during rupture, with Riedel shear bands—particularly R-shears—being most common. The friction coefficient of the fault gouge decreases in a two-stage linear trend with increasing clay content, with a steeper slope in the first stage, indicating a faster reduction in friction. Comparative analysis of different clay mineral combinations reveals that montmorillonite consistently plays the dominant role in controlling the mechanical properties of granite fault gouge, whether in binary or ternary mixtures.
Peer Review Status:
Awaiting Review
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