Bearing effect of prestressed bolt-anchored structures and mechanical analysis of surrounding rock
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摘要: 隧道中锚杆与围岩作用机理比较复杂，设计多偏于类比法和经验法，以锚杆在连续均匀地层中形成锚固结构为出发点，建立锚固结构承载强度表达式，并确定锚杆设计参数。通过对锚固结构承载特性分析，得到各影响因素对承载强度的贡献程度，在此基础上提出了“支护力放大系数”和“锚固界限强度”概念，再将锚固结构整体考虑并等效成支护力对隧道围岩应力分布、塑性区、位移进行重新求解，最终结合数值模拟和算例验证。研究结果表明：锚固结构对锚杆支护力具有放大作用，对隧道深部围岩也提供一个较强的支护力，锚固结构强度影响程度由大到小依次为力学参数、锚固厚度、支护强度，其中力学参数对锚固承载强度起着至关重要作用，合理锚固厚度为洞径的0.4~0.8倍，进一步提出了围岩稳定性控制原则。数值模拟中锚杆支护、等效力支护与理论结果加以比较，隧道周边的塑性区、应力分布、位移基本一致，可为锚杆支护下隧道围岩控制提供一种科学的分析方法。Abstract: Because of complicated interaction mechanism between bolt and surrounding rock in tunnels, the design is mostly based on the analogy method and experience. Starting from the anchorage structure formed by the bolt in continuously uniform strata, a formula for bearing strength is established, and the parameters in the formula are determined. By analyzing the bearing characteristics of anchorage structure, the influence degree of different factors on the bearing strength can be obtained. On this basis, the definitions of "amplification factor of supporting force " and "strength of anchor circumscription" are put forward. Besides, the anchorage structure can be equivalent to the support stress so as to resolve the stress distribution of tunnel surrounding rock, plastic zone and displacement, which is verified by the numerical simulation and numerical example. The results show that anchorage structure has an amplification effect on bolting force and provides a strong supporting force in the surrounding rock of deep tunnel. The influence degree structure for the strength of anchorage is followed by mechanical parameters, anchoring thickness and supporting strength from large to small, among which the mechanical parameters play a crucial role in the bearing strength of anchorage, and the reasonable anchoring thickness is 0.4~0.8 times the diameter of the tunnel. Furthermore, the stability control principle of surrounding rock is proposed. By comparing the theoretical results with the bolt support and equal effectiveness support in the numerical simulation, the plastic zone, stress distribution and displacement around the tunnel are basically the same. The proposed theories may provide a scientific analysis method for the stability control of the tunnel with bolt support.
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图 2 岩体支护前后应力屈服轨迹
Figure 2. Stress yield trajectories before and after rock mass support
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图 4 力学参数q，b与承载强度q关系
Figure 4. Relationship among mechanical parameters q, b and bearing strength q
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图 10 未支护围岩最大主应力分布
Figure 10. Distribution of maximum principal stress of unsupported surrounding rock
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图 11 锚杆支护围岩最大主应力分布
Figure 11. Distribution of maximum principal stress of surrounding rock supported by bolt
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图 12 等效力支护围岩最大主应力分布
Figure 12. Distribution of maximum principal stress in surrounding rock under equal effective support
表 1 分析参数
Table 1 Analytical parameters
原始参数 开挖扰动参数 支护参数 参数 数值 参数 数值 参数 数值 r0/m 2 — — LS /mm 2400 po/MPa 2 — — QS /kN 80 ν 0.2 — — SL*ST/mm 800*800 σci/MPa 50 GSI 40 d /mm 22 E/MPa 5000 Em/MPa 3976.4 Em*/MPa 4101.1 c/MPa 0.276 cp 0.055 cp* 0.058 φ/(°) 35 φp 30 φp* 33.5 
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表 2 塑性区范围比较
Table 2 Comparison of plastic zones
(m) Fenner解 理论值 锚杆支护 等效力支护 2.57 4.89 4.71~4.92 4.63~4.94
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