基于微台阶法对连拱隧道稳定性的研究

为研究软弱围岩基于微台阶法连拱隧道合理的掌子面纵向间距、仰拱一次开挖长度和开挖进尺施工参数,确保隧道安全和高效施工,以云南省元蔓高速公路风口山隧道为研究对象,从力学机理上分析了施工参数对隧道稳定的影响,采用数值模拟方法,分析纵向间距对中隔墙水平位移和开挖面叠加效应的影响、仰拱一次开挖长度对拱腰水平位移和中隔墙受力的影响、开挖进尺对围岩变形特征和掌子面剪应力的影响,对连拱隧道微台阶法进行最优化设计。结果表明,掌子面纵向间距2D、仰拱一次开挖长度4 m、开挖进尺2m为宜,可为类似连拱隧道的施工提供指导。

Study on the double-arch tunnel stabil-ity based on the micro bench theoreti-cal method

The given paper intends to present a study on the rationale and reasonable design of the construction parameters of the double-arch tunnel in Fengkoushan along the Yuanman Expressway in Yunnan under the fragile surrounding rock mass conditions in combination with the micro bench method. The key parameters,such as the longitudinal spacing of the faces,the excavation length of the inverted arch in one step and excavation footage,are to be taken into account to ensure the safety and efficiency of the construction project of the double-arch tunnel.And,in the paper,we have carefully analyzed the influence of the construction parameters on the tunnel stability and solidness as a result of successful application of the mechanic-kinetic principle and the finite element method. The research results we have gained can be summarized and generalized in the following ways: When the longitudinal spacing of the faces is less than 2D,the horizontal displacement of the interior wall may experience a quick growth with the increase of the special facets. Otherwise,the displacement would increase slowly with the widening of the spacing(the inverted arch is likely to prevent the displacement of the internal wall in case when it goes to push the palm face in turn consequently). Besides,in case the longitudinal spacing of the faces is greater than 2D,the first hole of the vault settlement would suffer a minor increment due to the excavation of the next cave. Otherwise,the increment would grow quickly with the reduced spacing. And,in such a situation,the ratio of the increment between 24 m and 16 m to that between 32 m and 24 m in the settlement would become greatest. And,when the excavation length of the inverted arch in one step is increasing from 5 m to 6 m,the horizontal displacement of the arch waist may grow quickest. For example,when the length increases from 4 m to 5 m,the increments of the first,third principal stresses and the maximum shear stress at the corner of the wall should become quickest with the ratio of the increment reaching the greatest in the displacement between 5 m and 6 m to the ratio between 4 m and 5 m. The greatest increment of the vault settlement can be made to rise to the excavation foot from 2 m to 3 m.And,then,when the footage is greater than 2 m,the maximum shear stress of the face would begin to increase steadily. The greatest ratio of the increment in the settlement and the shear can be made to reach between 2 m and 3 m to that between 1 m and 2 m. Thus,the optimal condition should be settled at the longitudinal spacing of facets at 2 D,with the excavation length of the inverted arch being at one step being 4 m and with the excavation footage being at 2 m. Hence,the above discussion should be acknowledged qualified enough to provide a scientific basis and technical guide for the construction of the double-arch tunnel.