Study on the effect of water on electromagnetic radiation characteristics of fractured sandstone under load

A large number of electromagnetic radiation (EMR) signals are released during loading failure of rock mass, and these signals which contain complex and abundant fracture information can provides precursor of rock mass instability. In order to investigate the effect of water on the EMR characteristics of fractured sandstone, a uniaxial compression experiment was performed on the dried and saturated sandstone samples with prefabricated parallel double cracks. The EMR signals during loading failure of rock samples were acquired and their mechanical properties and EMR signal characteristics were analyzed. Besides, the precursor of rock sample instability was extracted based on the critical slowing down theory. The experimental results show that compared with the dried rock sample, the saturated rock sample has lower compressive strength, starts to crack earlier, and exhibits a more complicated failure mode. During the loading failure of rock samples, their EMR signals respond well to the fracturing and damage. The cumulative number of pulses of saturated rock sample grows uniformly, while that of dried rock sample show a "gentle-violent" rising mode. Moreover, the cumulative number of pulses of dried rock sample is greater than that of saturated rock sample. Water reduces the crack initiation stress level, and the saturated rock sample is the first to experience a sudden jump of EMR pulse. With the increase of the loading stress, the dominant frequency of EMR gradually transitions from low frequency to high frequency. Compared with dried rock samples, saturated rock samples have a lower proportion of high-frequency signals. Since the dominant mechanism of EMR varies with the change of failure stage, water first promotes the EMR signals of rock samples in the early stage of loading; then, it weakens the EMR signals in the middle and late stages of loading. Based on the critical slowing down theory, the EMR pulse signals were analyzed, which conduces to the extraction of potential precursor of rock sample failure and instability. Compared with dried rock samples, the precursory characteristic of saturated rock sample is more obvious. The research results provide some guidance for the stability of water-bearing fractured rock mass and the monitoring and early warning of related geological hazards.