Model test study on bearing effect prestressing anchors in shallow buried tunnels
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摘要:
预应力锚杆主动支护技术在隧道工程中的应用逐渐普及，对于浅埋大跨岩质隧道，其支护特性及作用机制尚未明确。为探究预应力锚杆支护体系下围岩的承载特性，以青岛地铁6号线某暗挖车站为工程背景，基于相似原理配制地层及支护结构模型实验材料，通过液压加载试验，探究了预应力锚杆及普通锚杆支护下锚固体的承载特性。结果表明：①预应力锚杆与围岩的相互作用形成了具有承载能力的锚固体，能够有效承担大部分上覆荷载。预应力锚杆的应用使得隧道失稳破坏的预警荷载值提高了42.8%，同时极限荷载值也提高了41.2%。②在上覆加载过程中，预应力锚杆经历了紧密锚固持荷阶段和脱锚卸荷阶段，衬砌经历了应变累积、应变突增和应变释放3个阶段。③较普通锚杆，主动支护下预应力锚杆与岩体间的受力协同性好，无轴力突变现象，锚杆的支护性能得到充分的利用，有效抑制了裂隙的发育，提高了隧道的整体稳定性。
Abstract:The use of prestressing anchor active support technology in tunnel engineering is becoming morecommon.However, the support characteristics and mechanism of action have not been fully understood for shallow, large-span rocky tunnels.In order to investigate the bearing characteristics of the surrounding rock under the prestressed anchor support system, a concealed excavation station of Qingdao Metro Line 6 was used as the engineering background, and based on the similarity principle of formulating experimental materials for stratum and support structure modelling, the bearing characteristics of the anchors under the prestressed anchor and ordinary anchor support were investigated by hydraulic loading tests.The results indicate that: ① The interaction between prestressed anchors and the surrounding rock creates a load-bearing anchor solid that can effectively support most of the overlying loads.The application of prestressed anchors during the overburden loading process increased the warning load value of tunnel instability damage by 42.8% and the ultimate load value by 41.2%.② The overburden loading process involved the prestressing anchors going through the tight anchorage load holding stage and the de-anchorage unloading stage.Simultaneously, the lining underwent the strain accumulation stage, strain surge stage, and strain release stage during the overlay loading process.③ The prestressed anchor under active support has better force synergy with the rock body than an ordinary anchor, without the axial force mutation phenomenon.This allows the support performance of the anchor to be fully utilized.Additionally, the prestressed active support effectively inhibits the development of fissures and significantly improves the overall stability of the tunnel.
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Key words:
- Shallow buried large span tunnel /
- prestressing anchors /
- active support /
- anchor solid /
- model test
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图 4 太沙基浅埋隧道围岩压力计算示意图
Figure 4. Schematic of rock pressure calculation for shallow buried tunnels at Terzaghi base
图 10 不同上覆加载作用下围岩压力变化
Figure 10. Pressure variation of surrounding rock under diverse overburden loads
图 11 不同上覆荷载作用下锚杆轴力变化曲线
Figure 11. Anchor shaft force variation under different overburden load
图 15 上覆加载作用下隧道围岩宏观破坏特征
Figure 15. Macroscopic damage characteristics of tunnel's surrounding rock under overburden loading
表 1 车站地质参数
Table 1. Geological parameters of the station
地层 弹性模量E/MPa 泊松比μ 黏聚力c/MPa 内摩擦角φ/(°) 密度ρ/(kg·m-3) 微风化花岗岩 2 000 0.34 0.40 47 2 400 
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表 2 相似材料正交试验
Table 2. Orthogonal test of similar materials
方案 砂胶比(骨料/胶结材料) 水膏比(水泥/石膏) 含水率/% 1 5∶1 2∶1 8 2 5∶1 1∶1 10 3 5∶1 1∶2 12 4 6∶1 2∶1 8 5 6∶1 1∶1 10 6 6∶1 1∶2 12 7 7∶1 2∶1 8 8 7∶1 1∶1 10 9 7∶1 1∶2 12
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表 3 抗压强度敏感性分析
Table 3. Sensitivity analysis of compressive strength
因素 比例 抗压强度/MPa 强度极差/MPa 砂胶比 5∶1 2.372 0.649 6∶1 1.938 7∶1 1.723 水膏比 1∶2 2.287 0.487 1∶1 2.008 2∶1 1.800 含水率/% 8 2.149 0.336 10 1.813 12 2.071
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表 4 单轴抗拉强度敏感性分析
Table 4. Sensitivity analysis of uniaxial tensile strength
因素 比例 抗拉强度/MPa 强度极差/MPa 砂胶比 5∶1 0.272 0.122 6∶1 0.195 7∶1 0.150 水膏比 1∶2 0.221 0.02 1∶1 0.201 2∶1 0.202 含水率/% 8 0.203 0.004 10 0.207 12 0.206
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表 5 三轴抗压强度敏感性分析
Table 5. Sensitivity analysis of triaxial compressive strength
因素 比例 抗压强度/MPa (围压0.2 MPa) 强度极差/MPa 抗压强度/MPa (围压0.4 MPa) 强度极差/MPa 砂胶比 5∶1 3.057 0.414 3.863 0.486 6∶1 2.647 3.543 7∶1 2.643 3.377 水膏比 1∶2 3.153 0.560 3.880 0.460 1∶1 2.700 3.637 2∶1 2.593 3.420 含水率/% 8 2.753 0.180 3.610 0.313 10 2.707 3.430 12 2.887 3.743
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表 6 相似材料力学参数
Table 6. Mechanical parameters of similar materials
容重/(N·m-3) 抗压强度/MPa 抗拉强度 内摩擦角 设计参数 23 1.91 0.229 MPa 47° 试验参数 23 1.91 0.223 MPa 47.4° 相对误差 — — 2.6% 0.8%
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表 7 上覆荷载作用下隧道失稳预警值、极限值
Table 7. Warning value and limit value of tunnel instability under overlying loading
kN 工况 预警荷载值 极限荷载值 预应力锚杆主动支护 500 600 普通锚杆被动支护 350 425
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