Experimental study on anchoring crack-resistance effects of prestressed anchor under impact loads
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摘要:
在采动应力、冲击动载作用下，深部巷道围岩原生裂隙进行发育、扩展、失稳是深部围岩动力灾害的重要诱因，通过锚杆支护增加破碎围岩完整性，抑制原生裂隙的再度扩展是预防围岩动力灾害的重要手段。为此，采用分离式霍普金森压杆试验系统开展端锚、全锚、让压+端锚3种锚固方式及端头锚固不同预紧力矩条件下预应力锚杆CCNBD试件的冲击动载试验，分析了预应力锚杆对岩体动态断裂韧性、裂纹起裂时间、裂纹扩展速度的影响规律，揭示冲击载荷作用下预应力锚杆锚固阻裂效应。研究结果表明：①预应力锚杆阻裂效应表现为提高岩体动态断裂韧性、延缓裂纹起裂时间与降低裂纹扩展速度；②高预紧力端头锚固与全长锚固均有助于锚杆发挥锚固阻裂效应，其强化顺序依次为全长锚固＞端头锚固＞让压+端头锚固，后者因让压结构补偿了裂纹扩展空间，弱化了锚固阻裂效应；③冲击载荷作用下加锚岩体变形破坏过程具有裂纹孕育阶段、裂纹扩展阶段、锚杆承载阶段3个阶段，高预紧力矩与全长锚固时锚杆轴向应力在裂纹扩展阶段增速最明显，锚杆锚固阻裂效应最明显。研究成果对深部动载巷道锚固支护工程具有一定的理论指导及借鉴意义。
Abstract:Under the action of mining stresses and impact dynamic loads, the development, expansion and instability of the primary fissures in the surrounding rock of deep roadways are an important cause for the dynamic disasters of the deep surrounding rock, and increasing the integrity of broken surrounding rock and inhibiting the re-expansion of the primary fissures by using the anchor supports are an important method to prevent the dynamic disasters in the surrounding rock. To this end, the impact dynamic load tests are performed on CCNBD specimens of prestressing anchor under different preloading moments of end anchor, and three anchoring methods of end anchor, full anchor and yield pressure + end anchor are adopted using the split Hopkinson pressure bar test system. The effects of various factors on the dynamic fracture toughness, crack initiation time and crack expansion rate of the anchored rock mass are analyzed to reveal the crack-resistance effects of the prestressed anchors under impact loads. The results show that: (1) The crack-resistance effects of the prestressed anchors improve the macro-dynamic fracture toughness of the anchored rock mass and delay the micro-crack initiation time and reduce the expansion rate. (2) Both the high preloading end anchorage and the full-length anchorage help anchors develop the crack-resistance effects. Their strengthening order is full-length anchorage > end anchorage > yield pressure + end anchorage. The third method weakens the crack-resistance effects because the yield pressure structures compensates for the crack expansion space. (3) The deformation and damage process of anchored rock mass under impact loads has three stages: crack breeding stage, crack expansion stage and anchor bearing stage. The axial stress of the anchor rod with high preloading moment and full-length anchoring has the most apparent growth rate in the crack expansion stage, and the crack-resistance effects are the most obvious. The research results have some theoretical guidance and reference significance for the anchorage support projects of deep dynamic load roadways.
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图 10 不同预紧力矩下加锚岩体典型裂纹扩展时程曲线
Figure 10. Typical time-history curves of crack expansion of anchored rock mass under different preloading torques
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图 11 不同锚固方式加锚岩体典型裂纹扩展时程曲线
Figure 11. Typical time-history curves of crack expansion of anchored rock mass by different anchoring methods
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图 13 加锚岩体典型裂纹扩展速度与裂纹尖端位置关系曲线
Figure 13. Typical crack expansion rate of anchored rock mass versus position of crack tip
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图 14 不同预紧力矩与锚固方式下裂纹平均扩展速度
Figure 14. Average crack expansion speeds under different preloading torque and anchoring method
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图 15 不同预紧力矩典型加锚岩体轴力时程曲线
Figure 15. Time-history curves of axial force of anchored rock mass under different preloading moments
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图 16 不同锚固方式典型加锚岩体轴力时程曲线
Figure 16. Time-history curves of axial force of a typical anchored rock mass by different anchoring methods
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图 17 加锚岩体冲击动载加载过程示意图
Figure 17. Time-history curves of axial force of a typical anchored rock mass by different anchoring methods
表 1 试件制备尺寸
Table 1 Sizes of specimen
直径D/mm 厚度B/mm 直切槽初始尺寸a0/mm 直切槽最终尺寸a1/mm 刀具半径as/mm 50 25 7 19 20 
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表 2 锚固系统力学参数
Table 2 Mechanical parameters of anchoring system
锚杆类型 直径/mm 延伸率/% 弹性模量/GPa 抗拉强度/MPa 屈服强度/MPa 现场锚杆 18 ≥20 200 ≥490 ≥335 模拟锚杆 3 ≥40 193 ≥515 ≥205
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表 3 预紧力矩对照
Table 3 Comparison of preloading torques
(单位: N·m) 实验室预紧力矩 0 2 4 6 8 10 现场预紧力矩 0 40 80 120 160 200
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表 4 试验方案
Table 4 Test programs
试件编号 厚度D/mm 直径B/mm 预紧力矩/(N·m) 锚固方式 W-0-1 25.0 50.0 0 无锚 W-0-2 25.0 50.0 W-0-3 25.1 50.0 D-0-1 24.9 50.0 0 端头锚固 D-0-2 25.0 50.1 D-0-3 25.0 50.0 D-2-1 25.0 50.0 2 端头锚固 D-2-2 25.0 50.0 D-2-3 25.0 49.9 D-4-1 25.1 50.0 4 端头锚固 D-4-2 25.0 50.0 D-4-3 25.0 50.0 D-6-1 24.8 50.1 6 端头锚固 D-6-2 25.0 50.0 D-6-3 25.0 50.0 D-8-1 25.1 50.0 8 端头锚固 D-8-2 25.0 50.0 D-8-3 25.0 50.0 D-10-1 25.0 49.8 10 端头锚固 D-10-2 25.1 50.0 D-10-3 25.0 50.1 Q-6-1 25.0 50.0 6 全长锚固 Q-6-2 24.9 49.9 Q-6-3 25.0 50.0 R-6-1 25.0 50.0 6 让压+端头锚固 R-6-2 25.0 50.0 R-6-3 24.9 50.0
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