干湿循环条件下煤矿砂岩分离式霍普金森压杆试验研究

由于降雨、季节引起地下水位升降等原因，地壳中岩体常处于干湿循环状态。为研究干湿循环对岩石动态力学性能的影响，以安徽恒源煤矿北风井-259 m处砂岩为研究对象，采用?50 mm变截面分离式霍普金森压杆试验装置，对长径比为0.5的煤矿砂岩试件经干湿循环作用后实施单轴冲击压缩试验，获得了砂岩动态单轴压缩应力-应变曲线。研究发现，由于自由水的Stefan效应，干湿循环1次对砂岩具有增强作用，单轴动态抗压强度最高；其后，随着干湿循环次数的增加，砂岩受水侵蚀物理弱化作用，砂岩动态单轴抗压强度呈乘幂关系降低，砂岩试件的冲击破碎块度逐渐变小。试验结果表明，干湿循环12次时砂岩动态抗压强度比干湿循环1次降低约24%，表现出较强的劣化效应。

Split Hopkinson pressure bar tests on sandstone in coalmine under cyclic wetting and drying

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.