Mechanical behavior and fracture mechanism of red-bed mudstone under varied dry-wet cycling and prefabricated fracture planes with different loading angles

Abstract

Red-bed mudstone is a common geological material in engineering construction in the Southwest region in China. Its initial fractures are easily influenced by the combined effects of dry-wet cycling and external loads. Therefore, evaluating the mechanical behavior and fracture mechanism of red-bed mudstone under dry-wet cycling and prefabricated fracture planes with different loading angles is of great significance. In this study, the cracked straight through Brazilian disc (CSTBD) specimens with a prefabricated crack were tested using an RMT testing machine. Multiple-scale analysis methods, including digital image correlation (DIC) and acoustic emission (AE) techniques, 3D scanning, and scanning electron microscopy (SEM), were employed to comprehensively analyze the mechanical evolution and fracture damage mechanism of mudstone under dry-wet cycling. The experimental results indicate that as the loading angle increases, the peak load gradually increases, while an increase in the number of dry-wet cycles leads to a decrease in peak load. At the same time, dry-wet cycling causes the expansion and connection of initial microcracks, forming weak layers that affect the morphology of the main crack and the distribution of secondary cracks. Furthermore, with an increasing number of dry-wet cycles, the acoustic emission count significantly decreases, and the relative high value range of acoustic emission count expands. 3D scanning results show that an increase in the number of dry-wet cycles results in rougher fracture planes, while an increase in loading angle generally increases the roughness of the fracture planes. Additionally, SEM observations reveal that with an increasing number of dry-wet cycles, intragranular fracture patterns and microcrack distribution become more widespread, and tensile and shear fracture patterns are also observed in the center of the fracture plane. These research findings have important practical value for evaluating the stability and reliability of red-bed mudstone under dry-wet cycling and prefabricated fracture planes with different loading angles.