低加载率范围内煤岩组合体冲击倾向性的率效应试验研究

以煤岩组合体为研究对象,进行4种不同量级下的低加载率(10-3~100MPa/s)单轴压缩试验,以抗压强度、弹性模量、冲击能量指数、弹性能量指数、归一化动态破坏时间为参量,考察加载率对煤岩组合体冲击倾向性的影响。研究结果表明:随着加载率的提高,煤岩组合体的承载失效结构由煤体转化为煤岩组合体,并存在明显的临界加载率现象。煤岩组合体的抗压强度和弹性模量在临界加载率以下保持在较低值,在临界加载率以上保持在较高值;冲击能量指数随着加载率的提高先增加后减小,在临界加载率附近出现最大值;弹性能量指数随着加载率增加而提高;修正动态破坏时间在临界加载率之前降低幅度较快,在临界加载率之后缓慢下降然后趋于平稳;综合判断煤岩组合体的冲击倾向性随加载率的增加划分为两个比较明显的水平,并且在临界加载率附近表现出较为明显的冲击倾向性突变。临界加载率效应可为现场条件下确定合适的工作面推进速度提供参考。

Rate effect on the burst tendency of coal-rock combined body under low loading rate range

Uniaxial compression tests with four different orders of magnitude under low loading rate range (10-3-100 MPa/s) were conducted for coal-rock combined body.The influence of loading rate on the burst tendency of coal-rock combined body was investigated by using compressive strength,elastic modulus,impact energy index,elastic energy index and normalized dynamic failure time.The results show that with the increase of loading rate,the bearing failure structure of coal-rock combined body is converted from coal to coal-rock combined body,and the critical loading rate is obvious.The compressive strength and elastic modulus of coal-rock combined body remains at a relatively low value under the critical loading rate,and changes to a high level above the critical loading rate.The impact energy index increases first and then decreases with the increase of loading rate,and reaches the maximum value near the critical loading rate.The elastic energy index increases with the increase of loading rates.The corrected dynamic failure time decreases rapidly before the critical loading rate,and then decreases slowly and tends to be stable after the critical loading rate.It can be concluded that the burst tendency of coal-rock combined body can be divided into two distinct levels with the increase of loading rate,and the mutation rate of burst tendency near the critical load rate is very obvious.The critical loading rate effect has a certain guiding significance for determining the suitable working face advancing speed in the field condition.