Study on the deformation mechanism and large deformation control method of a strongly weathered carbonaceous slate tunnel in western China
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摘要:
为解决国家兰海高速(G75)定西段岷县隧道在建设过程中原支护设计方案出现的软岩大变形问题, 通过软岩类型分析、围岩变形力学机制分析, 提出针对不同力学机制的力学转化对策, 引入在矿山及边坡等岩石领域广泛应用的高预紧力恒阻大变形锚索, 提出了"超前支护+长短NPR锚索优化布置主动支护+钢拱架+混凝土喷浆永久支护"的高预应力主被动联合支护技术。通过数值模拟和现场监测效果对比研究, 结果表明, 现场试验段围岩最大变形量仅为73 mm, 恒阻大变形锚索的预紧力均在280~300 kN范围内, 可见优化后不同支护技术均对围岩变形起到了控制作用, 有效发挥了恒阻让压支护的作用, 控制效果明显。
Abstract:In response to the significant soft rock deformation challenges encountered during the construction of the Minxian Tunnel along the Lanzhou-Haikou Expressway (G75), this study conducted a comprehensive analysis of soft rock types and the underlying mechanical mechanisms governing the deformation of the surrounding rock. It presented tailored mechanical transformation strategies to address diverse mechanical mechanisms. Also, it introduced the application of anchor cable with high pre-tightening force, constant resistance and large deformation, a proven solution widely employed in mining and rock engineering. Furthermore, the research proposed a high-prestress and active and passive combined support technique, encompassing pre-reinforced retaining structure, optimally arranged active retaining structure with long and short NPR anchor cables, steel arches, and permanent retaining structure of shotcrete. By implementing numerical simulations and on-site monitoring, the results demonstrated a remarkable reduction in the maximum deformation of the surrounding rock in the test section to only 73 mm, and the pre-tightening forces applied to the anchor cable with constant resistance and large deformation ranged from 280 to 300 kN, underscoring the effectiveness of the optimized retaining technique in controlling surrounding rock deformation. This research highlights the pivotal role of retaining structure with constant resistance and yielding support, which significantly improves deformation control.
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表 1 黏土矿物成分相对含量统计表
Table 1. Statistical table of relative contents of clay mineral composition
编号 黏土矿物相对含量/% S I/S C/S It Kao C 1 / / / 69 6 2 2 / / / 60 5 35 3 / / / 66 / 34 4 / / / 47 / 53 5 / / / 62 / 38 注:S—蒙皂石类;I/S—伊蒙混层;It—伊利石;Kao—高岭石;C—绿泥石;C/S—绿蒙混层 表 2 全岩矿物成分相对含量统计表
Table 2. Statistical table of relative contents of the mineral compositions of the whole rock
编号 矿物含量/% 石英 黏土矿物 白云石 菱铁矿 黄铁矿 钾长石 石盐 1 56.3 39.6 3.2 / / / 0.9 2 35.2 55.1 / 6.1 / 2.2 1.4 3 62.4 18.6 14.4 / 1.1 2.7 0.8 4 68.6 22.8 4.6 2.8 / / 1.2 5 45.8 19.0 / 3.2 / 2.1 0.9 表 3 岷县隧道新型控制技术支护参数及原支护技术参数对比表
Table 3. Comparison table for support parameters of the new control technique and the original technique for the Minxian tunnel
原支护方案 新型支护方案 支护形式 支护参数 支护方式 支护参数 超前支护 小导管 ∅×L=42 mm×4500 mm,外插角10°,间排距350 mm×1200 mm 小导管 ∅×L=42 mm×4500 mm,外插角10°,间排距350 mm×1200 mm 初期支护 普通锚杆 全断面支护,∅×L=25 mm×3500 mm,间排距1000 mm×600 mm 短NPR锚索 全断面施工,∅×L=21.8 mm×7300 mm,间排距1000 mm×600 mm ∅×L=89 mm×3500 mm 长NPR锚索 拱顶施工,∅×L=21.8 mm×12300 mm,间排距2000 mm×600 mm 锁脚注浆锚管 拱顶施工,∅ 8 mm,框架尺寸150 mm ×150 mm 柔性网 型号JD PET120×120MS,网格尺寸100 mm×100 mm 钢筋网 C25混凝土,厚度260 mm W钢带 Q235钢:W×L=280 mm×3000 mm,孔径100 mm×100 mm 喷射混凝土 全断面I20a工字钢,排距600 mm 托盘 钢板:W×L×T=300 mm×300 mm×16 mm 钢拱架 钢拱架 全断面I20a工字钢,排距600 mm 喷射混凝土 C25混凝土,厚度260 mm 永久支护 钢筋砼衬砌 C30钢筋混凝土,厚度500 mm 钢筋砼衬砌 C30钢筋混凝土,厚度500 mm 注:∅为直径;L为长度;W为宽度;T为厚度 表 4 岩体力学参数
Table 4. Mechanical parameters of rock mass
材料 密度/(kg/m3) 弹性模量/GPa 泊松比 内聚力/MPa 内摩擦角/(°) 抗拉强度/MPa 法向刚度/GPa 剪切刚度/GPa 岩体 2500 1.05 0.25 0.8 21 0.5 - - 板理面 - - - 0.5 18 0.1 30 12 表 5 锚杆及锚索力学参数
Table 5. Mechanical parameters of bolt and anchor cable
横截面积/m2 弹性模量/GPa 抗拉强度/GPa 水泥浆黏结刚度/(N/m2) 水泥浆黏聚强度/Pa 预紧力/N 普通锚杆 3.79×10-4 210 0.182 2×107 2×105 70×103 普通锚索 3.73×10-4 200 0.445 2×107 3×105 150×103 NPR锚索 3.73×10-4 200 0.938 2×107 3×105 280×103 表 6 钢拱架-喷射混凝土等效支护体力学参数
Table 6. Mechanical parameters of the equivalent retaining structure of steel arch and shotcrete
钢拱架 混凝土型号 混凝土厚度/mm 等效容重/(kN/m3) 等效弹性模量/GPa 等效泊松比 I20a C25 260 23 31.55 0.20 HW175 C25 260 24 51.43 0.22 表 7 数值模拟方案
Table 7. Numerical simulation schemes
方案 变更内容 锚杆/m 钢拱架 原方案 原支护 3.5 I20a 方案a 更换钢拱架 3.5 H175 方案b 原锚杆—普通锚索 7 I20a 方案c 普通锚索(短+长) 7+12 I20a 方案d NPR锚索(短+长) 7+12 I20a -
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