Abstract: Under the complex unsymmetrical pressure geological conditions, the commonly used skew entering in tunnel portal area may cause large deformation and even overturning of the secondary lining. Based on Longmen Tunnel of Xiamen-Chengdu highway, the half-open arch portal construction scheme was put forward due to severe unsymmetrical loading conditions and over 30° skew angle disadvantageous situation. The three-dimensional finite element model was established and the construction mechanics response of the half-open arch structure was analyzed. The analysis results indicate that: compared with the traditional tunnel-entering scheme, the proposed method can effectively reduce the excavation height of the side slope and the disturbance to the surrounding rock; besides, the deformation and stress of half-open arch structure are also relatively reasonable. The proposed method has been successfully applied in Longmen Tunnel, which can provide reference for similar tunnel construction.

Key words: tunnel engineering, shallow buried bias tunnel, skew entering, half-open arch structure, three-dimensional finite element

摘要： 复杂偏压地质条件下，通常采用的斜交进洞方式存在隧道套拱变形量大，甚至倾覆等风险。基于厦蓉高速公路扩建工程龙门隧道洞口严重偏压、斜交超过30°等不利地形情况，提出半明拱进洞施工方案，并建立三维有限元模型，分析了半明拱结构的施工力学响应。分析结果表明：相较传统进洞方案，本工法可有效减少边仰坡开挖高度，及对洞口围岩的扰动；半明拱结构的变形与应力也较为合理。上述施工工法在龙门隧道得到了成功应用，可为类似条件隧道进洞施工提供借鉴。

关键词: 隧道工程, 浅埋偏压隧道, 斜交进洞, 半明拱结构, 三维有限元