After conducting true triaxial tests on sandstone in a laboratory setting, this study aims to determine the safe tunnelling rate of the roadway by examining the instability and failure characteristics of surrounding rock under different disturbance stresses in deep underground roadway excavation. Results showed that the mechanical properties, deformation, and failure characteristics of sandstone differed under different loading and unloading rates. Specifically, as the loading rate increased, the crack initiation stress increased while the damage stress remained unchanged, and the deformation anisotropy of the rock decreased. In contrast, as the unloading rate increased, the residual stress of the rock decreased, the brittleness increased, and the deformation anisotropy of the rock increased. Additionally, the expansion of the rock went through three critical stages: (1) A–B: a sharp increase in the dilatancy of sandstone (M) in a short period, accompanied by a large number of cracks, (2) B–C: a weakened stage of expansion ability, in which M continued to decrease over time, albeit at a slower rate, and (3) C–D: a stage of enhanced expansion ability, during which M began to increase again, albeit at a slower rate than its rate of decrease. This final stage was the longest.

No abstract

Establishing the relationship between the deformation of coal samples and acoustic emission response is the basis for the deformation prediction of coal samples. Using a combination of laboratory tests and theoretical analysis, acoustic emission tests of the uniaxial loading process were conducted on coal samples in the study area and the test results were analyzed, focusing on the rule of variation of acoustic emission counts with loading time. Based on the analysis of stress, strain, time, and acoustic-emission parameters variation, the relationship between the deformation of coal samples and acoustic emission response was established and analyzed. The analysis results show that during the loading process, the acoustic emission counts show the characteristics of stage changes, which can be divided into three stages: the initial stage with sporadic acoustic emission events, the middle stage with a stable increase of acoustic emission events, and the final stage with the rapid increase of acoustic emission events. This stage division has good consistency with the deformation stages of coal samples. Moreover, the acoustic emission counts have obvious and easily identifiable characteristics of changes in the deformation process of coal samples. The acoustic emission count can be used as a sensitive indicator in this study area to predict the deformation of coal samples. It provides a reference for the application of acoustic-emission prediction technology in this study area, which is important to improve the accuracy of geohazard prediction.

No abstract