Study on instability mechanism of anisotropic structural planes of coal and rock under unloading
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摘要: 目前针对岩体结构面滑移失稳方面的研究未考虑开挖过程中的卸荷效应，且对煤岩异性结构面的研究较少。为了探究触发煤岩异性结构面滑移的条件及其影响因素，通过建立异性结构面力学模型，理论推导了卸荷作用下异性结构面解锁滑移的判据，采用通用离散单元法程序（UDEC）建立平滑结构面数值模型，以验证理论分析异性结构面解锁滑移触发条件的准确性，分析异性结构面解锁滑移的影响因素。研究结果表明：煤岩异性结构面解锁滑移与结构面倾角、内摩擦角及水平应力与轴向应力的比值有关；当水平应力等于轴向应力时，异性结构面始终处于稳定闭锁状态，不会发生解锁滑移；水平应力和轴向应力增大、内摩擦角减小均会增大异性结构面解锁滑移难度；对于下行解锁滑移，当结构面倾角小于
$45^\circ + \dfrac{{{\varphi _{\rm{f}}}}}{2}$ （$\varphi _{\rm{f}} $ 为内摩擦角）时，其增大会增大解锁滑移难度，大于$45^\circ + \dfrac{{{\varphi _{\rm{f}}}}}{2}$ 时其增大会减小解锁滑移难度；对于上行解锁滑移，当结构面倾角小于$ 45^\circ - \dfrac{{{\varphi _{\rm{f}}}}}{2} $ 时，其增大会增大解锁滑移难度，大于$ 45^\circ - \dfrac{{{\varphi _{\rm{f}}}}}{2} $ 时其增大会减小解锁滑移难度；对于异性结构面稳定闭锁状态，结构面倾角不大于30°时，若轴向应力大于抗压强度，则煤岩组合体发生脆性破坏。Abstract: Currently, the research on the slip instability of rock mass structural planes has not considered the unloading effect during heading. There is relatively little research on the anisotropic structural planes of coal and rock. In order to explore the conditions and influencing factors that trigger the slip of anisotropic structural planes of coal and rock, a mechanical model of anisotropic structural planes is established. A criterion for unlocking slip of anisotropic structural planes under unloading is theoretically derived. A smooth structural plane numerical model is established using universal distinct element code (UDEC) to verify the accuracy of theoretical analysis of the triggering conditions for unlocking the slip of anisotropic structural planes. The influencing factors of unlocking slip of anisotropic structural planes are analyzed. The research results indicate that unlocking slip of anisotropic structural planes of coal and rock is related to the inclination angle of structural planes, internal friction angle, and the ratio of horizontal stress to axial stress. When the horizontal stress is equal to the axial stress, the anisotropic structural plane is always in a locked state without slipping. Increase of axial pressure and horizontal pressure and decrease of internal friction angle will increase the difficulty of unlocking slip on anisotropic structural planes. For downward unlocking slip, when the inclination angle of the structural plane is less than$45^\circ + \dfrac{{{\varphi _{\rm{f}}}}}{2}$ ($\varphi _{\rm{f}} $ is internal friction action), its increase will increase the difficulty of unlocking slip. When it is more than$45^\circ + \dfrac{{{\varphi _{\rm{f}}}}}{2}$ , its increase will reduce the difficulty of unlocking slip. For upward unlocking slip, when the inclination angle of the structural plane is less than$45^\circ - \dfrac{{{\varphi _{\rm{f}}}}}{2}$ , its increase will increase the difficulty of unlocking slip. When it is more than$45^\circ - \dfrac{{{\varphi _{\rm{f}}}}}{2}$ , its increase will reduce the difficulty of unlocking slip. For the locked state of structural plane, when the inclination angle of the structural plane is no more than 30°, if the axial stress is greater than the compressive strength, the brittle failure will occur in coal rock combination. -
图 3 异性结构面微小单元体结构力学模型
Figure 3. Structural mechanical model of tiny unit body of structural plane
图 4 结构面解锁与闭锁数值化结果
Figure 4. Numerical results of structural plane unlocking and locking
图 6 异性结构面下行解锁滑移位移云图
Figure 6. Displacement nephogram of downward unlocking slip of structural plane
图 7 不同因素对结构面下行解锁滑移的影响
Figure 7. Influences of different factors on downward unlocking slip of structural plane
图 8 异性结构面上行解锁滑移位移云图
Figure 8. Slip displacement nephogram of upward unlocking of structural plane
图 9 不同影响因素对结构面上行解锁滑移的影响
Figure 9. Influences of different factors on upward unlocking slip of structural plane
图 10 结构面倾角为25°时煤岩组合体应力−时间曲线
Figure 10. Stress-time curves of coal-rock combination at 25° of structural plane angle
图 11 结构面倾角为25°时煤岩组合体裂隙演化规律
Figure 11. Fracture evolution pattern of coal-rock combination at 25° of structural plane angle
表 1 模型块体参数
Table 1. Block parameters of the model
岩性 密度/（kg·m−3） 体积模量/GPa 剪切模量/GPa 岩 2 850 50 30 煤 1 600 30 20 
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表 2 模型结构面参数
Table 2. Structural plane parameters of the model
接触面 法向刚度/
（GPa·m−1）切向刚度/
（GPa·m−1）黏聚力/MPa 内摩擦角/（°） 非滑移区域 2 000 2 000 1.0 45 滑移区域 2 000 2 000 0 16
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