不同卸载速率下煤岩采动力学响应试验研究

深刻认识采动应力路径下岩体力学响应的加载速率效应，是科学界定实际工作面推进最优速率的重要基础。基于平煤矿区煤岩初始地应力环境，定量分析了千米级赋存深度煤岩保护层开采条件下应力演化特征，展开更为符合真实应力状态的不同加载速率下煤岩体力学行为实验模拟，同时与未考虑采动试验结果进行对比分析。研究结果表明：（1）常规三轴压缩试验，试样强度受加载速率影响较小，在1~4 MPa/min时并无明显变化，达到5 MPa/min时强度才有明显的上升，约为115 MPa。（2）随加载速率增加，采动过程中煤岩体强度呈现下降后上升再下降的趋势，1 MPa/min和4 MPa/min加载速率下煤岩体强度达到最大，其峰值应力约为64 MPa，较3 MPa/min提高了12%。（3）低加载速率下试件内部的微小裂隙可以充分发育、扩展，试样裂隙密度随加载速率增加呈减小趋势，其中1 MPa/min约为5 MPa/min的1.61倍，适当降低开采速度可提高瓦斯抽采效率。（4）不同开采速度煤岩在整个采动过程中体积应变不仅出现了相对初始状态的压缩现象，还出现了破坏阶段的体积膨胀，可将其作为采动特征，明显区别于未考虑采动下的体积压缩，且采动下煤岩强度明显偏小，破损程度更大。研究成果可为类似地质条件开展保护层开采设计奠定一定的理论基础。

Experimental Study on the Mechanical Response Mechanism of Different Unloading Rate to Coal Rock Mechanics

A deep understanding of the loading rate effect of rock mass mechanical response under mining stress path is an important basis for scientifically defining the optimal advancing rate of actual working face. Based on the initial crustal stress environment of Pingdingshan mining area, the evolution law of stress under the condition of protective layer mining with the depth of kilometer was analyzed quantitatively and the research on the mechanical behavior of coal and rock mass under different loading rates was carried out, which is more in line with the real stress state. At the same time, the comparative analysis with the results of tests without considering the mining was carried out. The results show that: (1) In the conventional triaxial compression test, the strength of the sample is less affected by the loading rate, and there is no obvious change at 1 ~ 4 MPa/min, and only when it reaches 5 MPa / min, the strength increases significantly, about 115 MPa. (2) With the increase of loading rate, the strength of coal and rock mass shows a trend of decreasing, rising and falling again. The strength of coal and rock mass reaches the maximum under the loading rate of 1 MPa/min and 4 MPa/min, and its peak stress is about 64 MPa, which is 12% higher than that of 3 MPa/min sample. (3) The micro cracks can be fully developed and expanded under low loading rate, and the fracture density of the specimen decreases with the increase of loading rate, in which 1 MPa/min is 1.61 times of 5 MPa/min, and the gas drainage efficiency can be improved by properly reducing the mining speed. (4) The volume strain of coal and rock in the whole mining process at different mining speeds not only appears the volume compression in the relative initial state, but also appears the volume expansion in the failure stage, which can be regarded as the mining characteristics, which is obviously different from that in the relative initial state without considering the mining test, which is always the volume compression; under mining. The strength of coal and rock is obviously smaller, and the damage degree is greater. The research results can lay a theoretical foundation for similar geological conditions to carry out protective layer mining design.