不同预静载水平下锚固结构扰动承载特性研究

Study on disturbance bearing characteristics of anchorage structure under varying pre-static load levels

  • 摘要: 动载扰动作用是影响深部煤炭资源开采过程中围岩稳定性的重要因素,分析扰动荷载作用下锚固结构的承载力学响应对巷道支护具有重要意义,本文采用FLAC–PFC(Fast lagrangian analysis of continua–Particle flow code)耦合的数值模拟方法对锚固试件进行了拉拔数值试验研究,分析了不同预静载水平下动载扰动对锚固结构力学特性、能量演化规律、破坏特征及损伤规律的影响. 研究结果表明:(1)动载扰动作用后,锚固试件峰值拉拔强度及对应位移均低于静载锚固试件,且随着预静载水平的增大,峰值拉拔强度和承载能力分别降低了4%~25%和7%~20%;(2)锚固试件的声发射振铃计数和累计振铃计数整体上呈平静期、稳定增长期和加速增长期的演化规律. 累计振铃计数随着预静载水平的增大从3309增加至4178;(3)预静载水平的增大导致锚固试件内部弹性能逐渐减小,耗散能逐渐增大,且弹性能始终大于耗散能. 耗散能占比与预静载水平呈正相关. 基于能量演化规律,可将弹性能耗比曲线在扰动后斜率由平稳转变为加速增长这一变化,作为锚固结构失稳破坏的前兆特征;(4)随着预静载水平增大,锚固试件内部力链数由1098减少至1009,裂纹分布范围逐渐由试件中上部向深部延伸;(5)随着预静载水平增大,锚固试件加载过程中初始损伤和扰动损伤分别增大了0.18和0.22,锚固结构更容易失稳破坏. 研究成果可为动载扰动作用下锚杆支护设计提供理论参考.

     

    Abstract: Dynamic load disturbance is an important factor affecting the stability of surrounding rock during deep coal mining. It is crucial to analyze the bearing capacity response of anchorage structures under varying disturbance loads to ensure effective roadway support. In this study, the FLAC–PFC (Fast lagrangian analysis of continua–Particle flow code) coupled numerical simulation method was used for the pull-out numerical test of anchorage specimens, and the influence of dynamic load disturbance on their mechanical characteristics, energy evolution law, failure characteristics and damage law were analyzed under varying pre-static load levels. The results showed that the pre-static load level had a significant effect on the disturbance-bearing capacity of the anchorage structure. When the pre-static load did not exceed the yield strength of the static load anchorage specimen, the peak pull-out strength and displacement were reduced by 4% and 7%, respectively, compared with the static load anchorage specimen (the pre-static load of anchorage specimen is 0), and the mechanical properties did not change significantly. When the pre-static load exceeded the yield strength, the accumulation of pre-static load damage led to a linear deterioration in the mechanical performance under dynamic load disturbance, and the peak strength and displacement decreased by 25% and 20%, respectively. In practical engineering, it is suggested that the upper limit stress of the disturbance load should be maintained at below 80% of the static load peak stress to avoid disturbance damage caused by the accumulation thereof. Overall, the evolution law of the acoustic emission and cumulative ringing counts of the anchorage specimens entailed the quiet, stable growth, and accelerated growth periods. The cumulative ringing count increased from 3309 to 4178 with increasing pre-static load levels. The increase in the pre-static load level led to a decrease in elastic energy and an increase in dissipation energy, and the former was invariably greater than the latter. The proportion of dissipated energy was positively correlated with the pre-static load level. Based on the law of energy evolution, the slope of the elastic energy consumption ratio curve can change from stable to accelerated growth after disturbance, which can be used as a precursory feature of instability and failure of anchorage structures. As the pre-static load level increased, the number of internal force chains decreased from 1098 to 1009, and the crack distribution range gradually extended from the upper part of the specimen to the inner part. The damage variable of the entire loading process of the anchorage specimen was defined, and the degree of damage under pre-static load was quantitatively analyzed. With increasing pre-static load levels, the initial damage and disturbance damage of the anchorage specimen increased during the loading process, and the anchorage structure became more prone to instability and failure.

     

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