煤岩组合体应力传递与强度特征倾角效应

Dip effect of stress transfer and structural instability mechanism of coal-rock combination

大倾角煤层安全高效开采的关键在于对围岩稳定性的有效控制,揭示煤岩组合体采动力学行为倾角效应是大倾角煤层多尺度围岩协同控制的基础。针对煤岩组合体在不同倾角时的层间应力传递、主应力偏转及非均衡变形破坏等力学特征,采用岩石力学试验、数值模拟与理论分析综合互馈的研究手段,分析了煤岩组合体内部主应力展布形态以及变形破坏规律的倾角效应。结果表明:倾角在0°~60°变化时,交界面处的煤岩组合体主应力大小和方向的演化特征分为2类;当层面倾角小于临界倾角α0时,煤岩组合体第1主应力随倾角增大而减小,第3主应力呈“煤减+岩增”的单调演变趋势,主应力方向呈“煤顺+岩逆”的偏转状态;当层面倾角大于临界倾角α0时,煤岩组合体第1主应力随倾角增大而增大,第3主应力变化幅度增大,主应力方向呈“煤逆+岩顺”的偏转状态;煤岩组合体受倾角影响时的2种状态的力学特征不同使得煤岩组合体由“交界面上侧岩体+非交界面部分煤体”转变为“交界面下侧煤体+非交界面部分煤体”的组合破坏模式,即对应于组合体的剪切变形破坏规律向界面处的滑移破坏规律的转变,因而煤岩组合体的强度随倾角增大而降低。研究结果揭示了煤岩组合体应力非均衡传递规律及其破坏机理的倾角效应,对大倾角煤层安全高效开采具有一定的理论参考意义。

The key to safe and efficient mining of steeply dipping coal seams is an effective control of surrounding rock. Revealing the dip effect on mining mechanical behavior of coal-rock combination are the basis for the multi-scale surrounding rock collaborative control in steeply dipping coal seams. According to mechanical characteristics of coal-rock combination such as stress transfer between layers, principal stress deflection and non-equilibrium deformation and failure at different inclination angles, the dip effect of principal stress distribution and deformation and failure law in coal-rock combination is analyzed by research methods of rock mechanics experiment, numerical simulation and theoretical analysis combined with feedback. The results show that: when the angle changes in the range of 0°–60°, the evolution characteristics of the size and direction of the principal stress of the coal-rock combination at the interface are divided into two categories;When the dip angle is less than the critical angle α0, the first principal stress decreases with the increase of the dip angle, the third principal stress exhibits a monotonic evolution trend of “coal decrease + rock increase”, and the principal stress direction is a deflection state of “coal clockwise + rock counterclockwise”. When the angle is larger than the critical angle α0, the first principal stress of the coal-rock combination increases with the increase of the angle, the variation of the third principal stress increases, and the principal stress direction is in the deflection state of “coal counterclockwise + rock clockwise”. When the coal-rock combination is affected by the dip angle, the mechanical characteristics of the two states are different, so that the combined failure mode of coal-rock combination changes from “the rock mass on the upper side of the interface + non-interface part of the coal body” to “the lower side of the interface + non-interface part of the coal body”. That is, corresponding to the transformation of the shear deformation failure law of the composite body to the slip failure law at the interface. Therefore, the strength of coal-rock combi-nation decreases with the increase of dip angle. The research results reveal the non-equilibrium transfer law of stress in coal-rock combination and the dip effect of its failure mechanism, which has certain theoretical reference significance for the safe and efficient mining of steeply dipping coal seams.