Research on the shear failure behavior and acoustic emission characteristics of natural sandstone structural surfaces after high-temperature treatment

Abstract

As one of the elements constituting the rock mass structure, the structural plane plays a controlling role in the stability of rock mass engineering. For rock mass engineering in high-temperature environments, studying the shear failure characteristics of structural planes under high temperatures is of great significance for revealing the instability mechanism of rock masses. Using the operation and maintenance of tunnels with yellow sandstone geological structures in high-temperature environments as the engineering background, samples were taken on-site, and precision carving technology was used to produce natural yellow sandstone structural plane samples with the same morphology. Shear tests and acoustic emission monitoring were conducted on the natural sandstone structural surface specimens under different high-temperature treatments (200 °C, 400 °C, 600 °C, and 800 °C) and different normal stresses (5 MPa, 10 MPa, and 15 MPa). The shear characteristics of sandstone structural surfaces after different high-temperature treatments, changes in morphology after high temperature and shear effects, and acoustic emission characteristics during the shear process were analyzed. The results show that the roughness of JRC_t of the structural surface specimens decreases with increasing treatment temperature, and the roughness of JRC_s of the specimens after shear also decreases. When the temperature reaches 600 °C, JRC_t decreases by approximately 20%, and the volume and mass damage caused by shear increase with temperature. Heat treatment significantly affects the shear curve of the structural surface, with a 39% reduction in shear strength at 800 °C under normal stress of 5 MPa compared to room temperature specimens. The temperature effect becomes less significant with increasing normal stress. The higher the treatment temperature, the later the onset time of intensive AE events, and the more concentrated the period of intensive AE events occurrence. At the same time, the fewer the ringing counts, energy, amplitude, cumulative ringing counts, and cumulative energy, the more evenly distributed the AE events throughout the entire shear process. The inflection magnitude of cumulative energy is greater than that of ringing count and time curve, and it occurs earlier than the cumulative ringing count, shear AE energy exhibits the best sensitivity to temperature. Higher AE energy mainly occurs during the post-peak damage stage, with the energy release caused by structural surface damage being more intense than rock fractures. With increasing temperature, the number of AE events decreases, the AE energy at the same position significantly decreases, and the range of AE signal localization becomes narrower and more concentrated near the structural surface. Structural surface damage is in good agreement with the acoustic emission location map, indicating that acoustic emission can well reveal the damage characteristics of structural surfaces. Shear wear occurs in specific local areas leading to shear failure, and nibbling fractures mainly occur at protrusions, with the energy released by nibbling fractures being greater than that released by frictional wear. This study aims to provide experimental evidence for the shear mechanism of the yellow sandstone structural plane. The combination of direct shear tests on structural surfaces and acoustic emission tests can be applied to monitor and predict the shear failure characteristics of engineering rock mass structural surfaces. This is crucial for early warning and prevention of rock engineering disasters.