八达岭长城站大跨过渡段最大开挖跨度为32. 7 m,开挖面积为494. 4 m2,是目前世界上开挖跨度最大、开挖断面面积最大的交通隧道,施工难度大,安全风险高.为确保八达岭长城站施工安全,对超大断面隧道的支护参数设计、开挖新方法以及围岩变形控制原则进行研究.研究表明: 1) 采用设计的支护体系,通过检算得到施工期安全系数为1. 16 ～ 2. 46,运营期安全系数为1. 59 ～3. 54,证明工程结构是安全可靠的;2) 超大跨度、超大断面隧道采用创新的"品"字形开挖方法,具有"方法简洁清晰、结构安全可靠、机械化程度高、施工效率高"的特点;3) 八达岭长城站大跨过渡段总变形量控制标准,按不同围岩级别和不同跨度划分,Ⅱ级围岩总沉降值为20 ～ 30 mm、总水平收敛值为15 ～ 20 mm,Ⅲ级围岩总沉降值为30 ～ 40 mm、总水平收敛值为20 ～ 25 mm,Ⅳ级围岩总沉降值为60 ～ 90 mm、总水平收敛值为40 ～ 55 mm,Ⅴ级围岩总沉降值为130 ～ 180 mm、总水平收敛值为90 ～ 105 mm;4) 采用数值模拟计算"品"字形开挖方法的变形量主要集中在隧道成拱阶段,约占总变形量的95％;其次是落边阶段,占总变形量的4％;最后是仰拱实施阶段,仅占总变形量的1％.%The large-span transition section at Badaling Great Wall Station with a maximum excavation span of 32. 7 m and an excavation area of 494. 4 m2 is the traffic tunnel with the largest excavation span and excavation section area in the world, resulting in substantial construction difficulty and high safety risk. To ensure the construction safety of Badaling Great Wall Station, the support parameter design, a new excavation method, and the surrounding rock deformation control principle for tunnels with an ultra-large section are studied. The study results show that: (1) According to the checking calculation, the support system had a safety factor of 1. 16-2. 46 during the construction period and 1. 59-3. 54 during the operation period, i. e., its engineering structure is safe and reliable. (2) The innovative triangle-type excavation applied to the tunnel with an ultra-large span and section has the advantages of a simple and clear method, safe and reliable structure, high applicability of mechanical equipment and high construction efficiency. (3) Depending on different surrounding rock classes and spans, the criteria for total deformation control of the large-span transition section at Badaling Great Wall Station are as follows: in the case of class Ⅱ surrounding rock, the total settlement is 20-30 mm, and the total horizontal convergence is 15-20 mm; in the case of class Ⅲ surrounding rock, the total settlement is 30-40 mm, and the total horizontal convergence is 20-25 mm; in the case of class Ⅳ surrounding rock, the total settlement is 60-90 mm, and the total horizontal convergence is 40-55 mm; in the case of class Ⅴ surrounding rock, the total settlement is 130-190 mm, and the total horizontal convergence is 90-<&&>105 mm. (4) According to the numerical simulation, the innovative triangle-type excavation method results in deformation that is mainly centralized in the tunnel arch-making stage, accounting for approximately 95％ of the total, followed by deformation in the side-making stage, accounting for 4％ of the total, with the smallest deformation only accounting for 1％ in the inverted arch-making stage.
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