无中导洞连拱隧道掌子面纵向间距优化

作为一种大跨径地下结构形式连拱隧道结构复杂，无中导洞法能在提高施工速度的基础上降低中隔墙渗漏水。为研究连拱隧道无中导洞法施工活动对隧道先后行洞的影响程度，以陈家滩隧道为研究对象通过数值模拟，研究了不同间距下先后行洞的影响范围、先后行洞的影响程度以及中隔墙的倾覆趋势。结果表明：当先行洞开挖至控制截面5m范围内对围岩的影响最大，其围岩位移释放系数增量达到了40%以上；超过控制截面10 m时其围岩释放系数达到了93%以上，影响程度较小；超过20 m时影响程度可以忽略。当先后行洞纵向间距大于35 m时影响程度S值接近10%，纵向间距大于40 m时S值小于10%。从中隔墙的倾覆程度来看当先行洞开挖完成时，中隔墙的倾斜程度达到最大，倾斜角约为3.28×10-4；而纵向间距大于30 m时倾斜角差值为0.351×10-4，此时中隔墙倾斜程度较大极差较小，有利于中隔墙受力。故先后行洞开挖掌子面纵向间距建议控制在30 m~40 m左右。

Study on optimization of longitudinal spacing of multi-arch tunnel without middle guide tunnel

As a kind of long-span underground structure, a multi-arch tunnel has a complex structure. The method without a middle guide tunnel can reduce water leakage of the middle partition wall based on improving construction speed. The purpose of this research is to study the influence degree of the construction activities of a multi-arch tunnels without a central guide tunnel on successive tunnels. Taking Chenjiatan tunnel as the research object, the deformation of the surrounding rock, the influence degree of successive tunnels, and the overturning trend of the middle partition wall under different spacing are studied by numerical simulation. The results show that when the first tunnel is excavated to the control section within 5 m, the influence on the surrounding rock is the largest, and the displacement release coefficient of surrounding rock increases by more than 40 %. When the control section is more than 10m, the release coefficient of surrounding rock reaches more than 93%, and the influence degree is small. When the control section is more than 20m, the influence degree can be ignored. When the longitudinal spacing is greater than 35m, the S value of the influence degree is close to 10%, and when the longitudinal spacing is greater than 40m, the S value is less than 10%. In terms of the overturning degree of the middle partition wall, when the excavation of the guide tunnel is completed, the inclination degree of the middle partition wall reaches the maximum, and the inclination angle is about 3.28 × 10-4; When the longitudinal spacing is greater than 30 m, the difference of inclination angle is 0.351×10-4. At this time, the inclination of the middle wall is large and the range is small, which is conducive to the stress of the middle wall. Therefore, it is recommended to control the longitudinal spacing of tunnel excavation face tunnel excavation about 30m~40m.