漂卵石隧道支护体系受力变形特性

Mechanical deformation characteristics of support system for boulder-cobble tunnel

针对川藏线拉萨—林芝段娘盖村隧道开挖与支护施工难、拱部塌落灾害频发等工程技术难题,提出了“三台阶互补循环式开挖+型钢钢架+喷射混凝土+双层密钢网+多组锁脚锚杆(管)+衬砌壁后注浆”的开挖支护组合体系,选取漂卵石隧道2组典型断面开展支护体系受力与变形实测研究,分析了围岩荷载作用特征、支护体系受力特性以及洞内外变形规律,揭示漂卵石隧道新型支护体系承载作用机制,总结提出了相应的防控新原则。分析结果表明:围岩压力以拱部松动塌落荷载为主且沿洞周分布不均,初期支护与二次衬砌平均荷载分担比例分别为67.65%和32.35%;锁脚锚杆受力拉压兼具,优化后最大拉、压力分别减小了45.9%和20.0%;二次衬砌受力总体较小,具有足够的结构安全储备;洞身段拱顶下沉不超过15 mm,水平收敛为8~9 mm;洞口段变形不对称且受浅埋偏压和降雨条件影响显著,拱部最大下沉达52.4 mm,上、下台阶水平收敛分别为11.4和15.6 mm,在类似不利条件下应尽早施作仰拱和二次衬砌以保证施工安全;漂卵石隧道支护体系设计遵循“少扰动、强拱脚、防超挖、密钢网、勤注浆”的防控原则,能够及时控制拱部松动区扩展,调动深层围岩的自承载能力,从而达到改善支护结构受力性能和有效避免拱部塌落灾害发生的目的。

In response to the engineering and technical problems such as the extreme difficulty in excavation and support construction,and the frequent collapse disasters at the arch in the Nianggaicun Tunnel of Lhasa-Nyingchi Section on the Sichuan-Xizang Line,a combination of excavation and support system containing"three-bench complementary cyclic excavation+section steel arch+shotcrete+double-layer dense reinforcement mesh+multiple groups of feet-lock bolts(pipes)+grouting behind the lining"was proposed.Two typical sections of boulder-cobble tunnel were selected to conduct the test research on the stress and deformation of the support system.The load action characteristics of the surrounding rock,the mechanical properties of the support system,and the deformation laws inside and outside the tunnel were analyzed.The load-bearing action mechanism of the new support system was revealed for the boulder-cobble tunnel,and corresponding new prevention and control principles were summarized and proposed.Analysis results show that the surrounding rock pressure is mainly a loose collapse load at the arch and distributes unevenly around the tunnel.The average load-sharing ratios of initial support and secondary lining are 67.65%and 32.35%,respectively.The feet-lock bolts are either tensile or compressive,and the maximum tensile and compressive forces reduce by 45.9%and 20.0%after optimization,respectively.The force of the secondary lining is overall small with enough structural safety reserve.The vault subsidence is less than 15 mm,and the horizontal convergence is 8-9 mm in the tunnel body.At the tunnel portal section,the deformation is asymmetric and significantly affected by the shallow bias and rainfall conditions.The maximum settlement of the arch part reaches 52.4 mm,and the horizontal convergences of the upper and lower benches are 11.4 and 15.6 mm,respectively.Under the similar unfavorable conditions,the inverted arch and secondary lining should be constructed as early as possible to ensure the construction safety.The support system design for the boulder-cobble tunnel follows the prevention and control principles of"less disturbance,strong arch foot,anti-overbreak,dense reinforcement mesh,and frequent grouting".It can timely control the expansion of the loose zone at the arch and mobilize the self-bearing capacity of the deep surrounding rock,achieving the purpose of improving the mechanical performance of the support structure and effectively avoiding the occurrence of arch collapse disasters.