Failure mechanism of coal under freeze–thaw conditions from the spectrum analysis of ultrasonic scanning data

The samples of anthracite and bituminous coal are studied in cyclic freeze–thaw at different water contents. In the freeze–thaw cycles, the samples were subjected to continuous ultrasonic sounding. It is found that different contents of water have an essential influence on the spectrum of recorded signals. Regarding the water-unsaturated check samples, the spectrum change is reversible, and the freeze–thaw treatment results in no failure. An increase in the water content of the samples fosters the irreversible change in the spectra of the signals against the background of macro-cracking along stratification planes. Anthracite exhibits higher persistence to freeze–thaw damage than bituminous coal.