Abstract: Cyclic wetting and drying usually occurs in rock mass during groundwater water level variation caused by rainfalls and season changing. In order to investigate the influence of cyclic wetting and drying on dynamic mechanical properties of rock, a series of uniaxial dynamic compression tests on sandstone under cyclic wetting and drying are carried out by ?50 mm variable cross-section split Hopkinson pressure bar (SHPB) apparatus. Sandstone specimens from Beifeng shaft -259 m of Hengyuan coalmine are processed into a cylindrical shape with a length to diameter ratio of 0.5. The corresponding dynamic stress-strain curves are obtained. It is found that as the Stefan effect of free water, wetting and drying 1 time gets a potentiation effect on sandstone; thus its dynamic uniaxial compressive strength is the highest. Then, with wetting and drying cycles increasing, dynamic uniaxial compressive strength reduces in a power relationship for physical weakening effect of water erosion; and the size of impact fragments becomes much smaller. The results show that when wetting and drying 12 times, dynamic uniaxial compressive strength of sandstone reduces about 24% compared with the result in wetting and drying 1 time, which shows a strong deterioration effect.

Key words: rock mechanics, split Hopkinson pressure bar (SHPB), wetting and drying cycle, dynamic strength, coalmine sandstone