软弱地层大断面铁路隧道进洞方法研究与实践

Research and Practice of Tunnel-entering Method of Large Section Railway Tunnel in Weak Strata

为解决软弱地层隧道洞口暗挖进洞施工的难题,以新建成昆铁路杨家湾隧道和西(安)成(都)高铁石梯子隧道为工程依托,采用理论分析与工程实践相结合的方法,对隧道洞口边仰坡稳定性及加固设计方法进行研究分析。研究结果表明,软弱地层隧道洞口上台阶开挖及开挖至路基面,仰坡安全系数均小于1,处于不稳定状态易形成潜在滑动面,开挖塌方风险大。基于隧道洞口稳定性分析,隧道仰坡滑塌必然存在潜在滑动面,洞口加固设计应以稳定滑动面为核心;基于该设计理念提出隧道洞口加固设计的3种方法,分别为玻璃纤维钻孔桩加固方法、桩基托梁护拱加固方法和纵横梁加固方法。3种方法的核心设计理念是通过洞口护拱或明洞对仰坡滑坡体形成反压,通过锚固桩或玻璃纤维桩抵抗潜在滑动面,并成功应用于新建成昆铁路杨家湾隧道和西成高铁石梯子隧道,保证隧道洞口的稳定性,并安全顺利暗挖进洞。

To solve the problem in subsurface excavation for entering tunnel construction in weak strata, the side and face upward slope stability and reinforcement design method of tunnel portal are studied and analyzed with reference to the new Yangjiawan Tunnel on Chengdu to Kunming railway and Shitizi Tunnel on Xi’an to Chengdu high-speed railway based on the combination of theory analysis with engineering practice. The results show that with upper bench excavating and excavating to formation level, and the face upward slope safety factor less than 1, the potential slip surface on account of the instability state is likely to form with great excavation collapse risk. Based on the stability analysis of face upward slope, potential slip surface is inevitably existed when the heading slope collapses and the stable slip surface should be taken as the key for portal reinforcement design. Based on the design concept, three reinforcement design methods are put forward: the glass fiber bored pile reinforcement method, the pile foundation underpinning protection arch reinforcement method and longitudinal-cross beam reinforcement method. The key design concept of the three methods is to form back pressure on the face upward slope through protection arch or open-cut tunnel, and to resist potential slip through anchor pile or glass fiber bored pile, which have been successfully applied to the new Yangjiawan Tunnel on Chengdu to Kunming railway and Shitizi Tunnel on Xi’an to Chengdu high-speed railway to guarantee tunnel portal stability and safe underground excavation.