Abstract: Coupling wetting-drying cycles and dynamic loading deteriorates the physical and mechanical properties of coalmine rock, damages underground structure and even induces geological hazards and accidents in coalmine underground engineering. In the light of longitudinal wave velocity variation and Weibull distribution statistical damage theory, we deduced the damage evolution equation of coalmine sandstone under coupling wetting-drying cycles and dynamic loading, and investigated the damage evolution with the dynamic elastic modulus determined by different methods. We found that the method of determining dynamic elastic modulus as the average slope between 30% and 70% peak stress on dynamic stress-strain curve is more suitable for the damage evolution rule of tested coalmine sandstone. Moreover, we further examined the influence of wetting-drying cycle on total damage variable and total damage ratio, and unveiled that under coupling wetting-drying cycles and dynamic loading, damage variable enlarged with the proceeding of cyclic wetting and drying, while damage ratio increased first and then reduced with the growth of dynamic strain. Finally, we built and validated a dynamic constitutive model for coalmine sandstone under coupling wetting-drying cycles and dynamic loading. The test results are expected to offer basis for the stability analysis in deep underground rock engineering.

Key words: coalmine sandstone, wetting-drying cycles, dynamic loading, dynamic elastic modulus, damage evolution, constitutive model