为揭示Ⅵ级富水软岩隧道围岩大变形机理及以双层初期支护为主的综合变形控制措施支护效果，以大瑞铁路杉阳隧道为例，基于软岩峰后刚度与强度劣化模型建立富水环境下Ⅵ级软岩隧道双层初期支护条件下的黏弹塑性解析式，借助工程监测数据与数值模拟验证后，分析相关影响因素。主要结论如下： 1）高地应力Ⅵ级富水软岩隧道开挖后围岩变形前期以挤压变形为主，后期以松动变形为主，围岩变形受岩性软弱、地下水软化、初期支护结构抗力不足等因素的影响较大； 2）以双层初期支护为主的“双层初期支护+开挖断面优化+浅部围岩注浆”综合变形控制措施能够有效控该类大变形，将围岩大变形控制在20 cm以下； 3）双层初期支护能够满足“先让压，后强支”的支护理念，其支护抗力pi越大，隧道围岩的总位移越小，pi对围岩后期蠕变变形的影响明显大于前期的瞬时变形； 4）高地应力软岩洞室双层初期支护施工过程中，外层初期支护由于施作较早导致总变形量较大，建议后续研发让压型双层初期支护。
To reveal the large deformation mechanism of surrounding rock in Grade Ⅵ water-rich soft rock tunnels and verify the supporting effect of comprehensive deformation control measures dominated by double-layer primary support, a case study is conducted on the Shanyang Tunnel of the Dali-Ruili Railway, and a viscoelastic-plastic analytical solution for Grade Ⅵ water-rich soft rock tunnels with double-layer primary support is established based on the post-peak stiffness and strength deterioration model of soft rock. Verified by field monitoring data and numerical simulation results, relevant influencing factors of surrounding rock deformation are systematically analyzed. The main conclusions are drawn as follows: (1) For high insitu stress Grade Ⅵ water-rich soft rock tunnels, the surrounding rock is dominated by compressive deformation in the early stage and loosening deformation in the later stage after excavation. The surrounding rock deformation is greatly affected by weak lithology, groundwater softening effect, and insufficient structural resistance of primary support. (2) The comprehensive control measures integrating double-layer primary support, optimized excavation section, and shallow surrounding rock grouting can effectively restrain the large deformation of such soft rock tunnels, limiting the surrounding rock deformation within 20 cm. (3) The double-layer primary support perfectly conforms to the support principle of “yielding pressure first and then strengthening support”. The total displacement of surrounding rock decreases with the increase of support resistance, and the support resistance exerts a far more significant influence on the late creep deformation than the early instantaneous deformation of surrounding rock. (4) In the construction process of double-layer primary support for high insitu stress soft rock caverns, the outer primary support suffers a larger total deformation due to the early installation time. The development of yielding-type double-layer primary support is recommended for follow-up related researches.
