节理岩体中纵向间距对连拱隧道稳定性的影响

为了研究双连拱隧道左右幅开挖对临洞的影响，以云南省晋红高速公路蔡官营隧道为研究对象，采用块体离散元软件3DEC中的黏结块体模型建立数值模型，模拟分析双连拱隧道一侧开挖对临洞拱顶沉降和围岩节理破坏范围的影响。研究结果表明：该模型能够合理地表征蔡官营隧道纵向间距过大或过小时现场出现的异常变形及结构破坏等现象；开挖过程中，无论是先行洞或后行洞开挖都会造成临洞拱顶沉降值增大及围岩中张拉、剪切破坏节理数量的增加，且破坏的节理主要以剪切滑动破坏为主，说明除了位移、应力外，节理破坏数量的变化也可作为围岩所受扰动大小的判断依据。然后以多个指标为判断依据，研究该隧道左右幅掌子面不同纵向间距对隧道围岩及支护结构的影响，进而确定合理的纵向间距；根据先行洞掌子面附近拱顶沉降值变化得出合理间距不小于30 m，根据张拉失稳节理面的数量得出合理间距为20~40 m，根据处于滑动状态的节理数量得出合理间距为30~40 m，根据发生滑动节理数总和得出合理间距为20~40 m，根据中隔墙的水平位移得出合理间距为20~40 m，根据二衬弯矩值得出合理间距不大于40 m，综合所有判断依据，得出隧道左右幅掌子面纵向间距应介于30~40 m（隧道净空的2~2.5倍）之间。在后续施工过程中，将左右幅掌子面纵向间距严格控制在该范围内，最终隧道顺利实现了贯通。

Influence of Longitudinal Spacing of Double-arch Tunnel on Tunnel Stability in Jointed Rock Mass

To study the influence of double-arch tunnel excavation on adjacent tunnel, the Caiguanying tunnel at Jinhong Expressway in Yunnan Province was selected for research. A numerical model was established by setting the bond block model method in the discrete element software named 3DEC. The settlement and the range of failure joints in surrounding rocks were simulated and analyzed. The simulation results show that the model can reasonably characterize the abnormal deformation and structural failure of the Caiguanying Tunnel when the longitudinal spacing is too large or too small. In the process of excavation, the settlement value and the number of tensile and shear failure joints in the surrounding rocks of the adjacent tunnel increase when the advance or the back tunnel is being excavated. The failure joints are mainly caused by shear sliding. Furthermore, based on a number of factors, the influence of different longitudinal spacing between the left and right working face of the tunnel on the stability of the surrounding rocks and supporting structure of the tunnel is studied to determine the suitable longitudinal spacing. The results show that this spacing should be greater than or equal to 30 m according to the variation of the settlement value of the vault near the working face of the advance tunnel. In terms of the number of tensile failure joints, the suitable spacing is 20-40 m. In terms of the sliding state, the suitable spacing is 30-40 m. In terms of the total number of slide failure joints, the suitable spacing is 20-40 m. A spacing less than or equal to 40 m is suitable in terms of the bending moment of lining. On the basis of all these judgments, it is concluded that the vertical spacing between two sides tunnel should be between 30-40 m, which is 2 to 2.5 times the tunnel clearance. In the subsequent construction process, the longitudinal spacing of the left and right working faces is strictly controlled within this range, and the tunnel is smoothly penetrated finally.