轴压和围压对循环冲击下砂岩能量耗散的影响

利用动静组合加载试验装置，对具有不同轴压和围压的砂岩进行循环冲击试验，研究循环冲击过程中砂岩单位体积吸收能的变化特性、单位体积吸收能与平均应变率的关系以及轴压和围压对循环冲击作用下岩石能量耗散的影响。围压分别设置为4、8、10、12 MPa等4个系列，轴向静载荷分别设置为49、84、105、125 MPa等4个系列，入射杆上的入射波峰值大小近似相等，入射能大小为230 J。研究结果表明，砂岩单位体积吸收能随循环冲击次数的增加而增加。平均应变率和单位体积吸收能具有良好的正线性关系，围压从低到高增加过程中，二者间拟合直线的斜率K随轴压增加的变化关系为“增加-基本不变-减小”。当轴压较小时，K随围压的增加先增加后降低，轴压越小K由上升到下降转折点处的围压越大；当轴压增加到125 MPa时，K随围压的增加始终降低。研究结果为具有不同地应力条件下工程岩体爆破设计提供理论依据。

Effects of axial compression and confining pressure on energy dissipation of sandstone under cyclic impact loads

Cyclic impact tests on sandstone under different axial and confining pressures are conducted with a modified three-dimensional split Hopkinson pressure bar (SHPB). The main research contents are change property of energy absorption per unit volume, relationship between energy absorption per unit volume and average strain rate, effects of axial compression and confining pressure on energy dissipation of sandstone under cyclic impact loads. Confining pressures are set as 4, 8, 10 and 12 MPa; and four levels of axial stresses are 49, 84, 105 and 125 MPa respectively. Incident waves in input bar are approximately equal and incident energy is equal to 230 J. The results show that energy absorption per unit volume increases with the increasing number of cyclic impacts, when the cyclic impact loadings are a constant. Energy absorption per unit volume has a good linear increasing relationship with average strain rate. The linear-fitted slope K of average strain rate and energy absorption per unit volume indicates a trend of “increase, constant, then decrease” with the increasing axial stress. When the axial stress is smaller, K increases and then becomes lower with the increasing of confining pressure. The smaller axial stress is, the bigger the confining pressure corresponding to slope’s turning point is. After the axial stress reaches to 125 MPa, K continually reduces with the increase of confining pressure. The conclusions may provide the theoretical basis for blasting design of rock mass engineering under different in-situ stress conditions.