Artificial freezing has been proved to be an effective method and technology to prevent water seepage and shaft flooding accidents in soft water-rich rock strata in western area of China. Many studies have been undertaken using frozen rocks to understand the mechanical and physical properties as well as their degradation mechanisms. However, the existing researches on the real-time dynamic damage process of frozen rocks are very limited, so that the damage mechanisms of frozen rock under compressive loading condition remain unknown. In this study, acoustic emission (AE) method and digital microscope were adopted to study the mechanical properties and microstructure of sandstone samples taken from Meilin Temple Mines at depth of 700 m in Ordos, China. The uniaxial compression tests were performed at four different sub-zero temperatures. The AE signals (e.g., energy) were recorded during freezing and loading processes at negative temperatures. The results showed that AE activities mainly occurred in the initial freezing phase and reduced afterwards. In the uniaxial compression test, AE signals were also observed in the initial loading stage, while no obvious results was observed from rock samples in room temperature. Based on the monitored acoustic emission data, the internal micro-crack change of frozen sandstone was revealed and the damage process was analyzed to evaluate the real state of frozen sandstone at the shaft construction site.
Coal has been the primary energy source in China for a long time, and the western region of China is one of the main production areas. In order to mine the coal in this region, vertical shafts are drilled through Cretaceous and Jurassic strata, which are characterized by high water content, low mechanical strength and loose cementation. Hence, it is of critical importance for the mining projects to study the mechanical properties of the typical rock in western areas (Liu et al., 2015).