基于竖向位移差的块系岩体超低摩擦效应理论分析

Theoretical analysis of anomalously low friction effect of block rock media based on vertical displacement difference

深部块系岩体在强冲击扰动下其相对压紧程度会随时间变化,引起超低摩擦效应,而块体间竖向位移差是表征块体间相对压紧程度的直观指标。以块系岩体为研究对象,建立了考虑上覆岩层压力的岩体动力模型,推导得出垂直冲击作用下新的块体间竖向位移差公式并与试验结果进行了对比,验证了理论公式的正确性。最后分析了块体间阻尼、块体质量、垂直冲击幅值和频率等影响因素对相邻两块体间竖向位移差影响规律并以其最小值变化判断超低摩擦效应发生难易程度。竖向位移差最小值越小,超低摩擦效应愈趋显著。研究表明:块体模型受垂直冲击扰动作用时,块体在时间尺度上依次发生强迫振动和自由振动,而其运动过程按竖向位移差变化可分为超强挤压、强挤压、弱挤压和相互脱离4个阶段,相互脱离阶段和弱挤压阶段是超低摩擦效应易发阶段;块体质量、结构面阻尼变化对竖向位移差幅值及周期有明显影响,块体间竖向位移差最小值随块体质量增加以对数规律递增、随块体间结构面阻尼增加以线性规律递增;块体质量和结构面阻尼越小,超低摩擦效应更易发生。垂直冲击频率和幅值亦对块体间竖向位移差影响显著,竖向位移差最小值随垂直冲击载荷幅值增加而线性递减,随垂直冲击频率增加以对数规律递增,即低频、强冲击扰动更易诱发超低摩擦型冲击地压。

Due to the strong impact disturbance,the relative compaction of deep block rock media changes with time and results in anomalously low friction effect.The vertical displacement difference between blocks is a visual indicator of the relative compression between the blocks.A dynamic model of block rock media considering the overburden pressure was established in this study.The new formula of vertical displacement difference between rock blocks subjected to vertical impact loading was derived and compared with the experimental results.It verified the correctness of the theoretical formula.The influence of various factors,including the mass of the block,the structural surface damping,the frequency and amplitude of vertical impact loading,on the regularity of the displacement difference between the blocks was analyzed.The occurrence of the anomalously low friction effect was assessed by the change of the minimum vertical displacement difference.The anomalously low friction effect occurs easily with the smaller minimum vertical displacement difference.The results show that when the block model is subjected to vertical impact disturbance,the block will go through forced vibration and free vibration.Its vertical movement can be divided into four stages:super strong extrusion,strong extrusion,weak extrusion and mutual separation according to the change of the vertical displacement difference.The phase of mutual separation and the weak extrusion are prone to induce anomalously low friction effects.The block mass and structural surface damping changes have a significant effect on the vertical displacement difference amplitude and period.The minimum value of the vertical displacement difference between blocks increases with the logarithm of the mass of the block,and increases linearly with the increase of the damping of the structural surface between the blocks.The smaller the block mass and structural surface damping,the more significant the anomalous low friction effect.The vertical impact loading frequency and amplitude make the vertical displacement difference between blocks change significantly.The minimum value of the displacement difference decreases linearly with the increase of the vertical impact loading amplitude,and increases in logarithm with the increase of the vertical impact frequency.The study concludes that low frequency and strong impact disturbance are more prone to induce anomalously low friction typels rock burst.