非对称连拱隧道不同开挖方案的比较分析

根据某高速公路非对称连拱隧道衬砌结构形式, 针对地表平、地表顺倾斜和地表逆倾斜等地表倾斜情况建立了相应的有限元分析模型, 选取围岩稳定性、衬砌安全性和偏压情况等反映隧道稳定性的性能指标, 采用数值模拟方法综合分析了不同地表倾斜情况下不同开挖方案对隧道稳定性的影响。结果表明, 地表倾斜状况显著影响非对称连拱隧道围岩和衬砌的受力和变形情况, 非对称连拱隧道地表平时应采用先大洞后小洞的开挖方案, 地表倾斜时必须综合考虑地表倾斜情况和大小洞的跨度差异, 才能合理确定开挖方案。非对称连拱隧道隧洞开挖时, 先开挖一侧的围岩应力释放会引起另一侧未开挖岩体的竖向应力增大, 导致另一侧岩体开挖时释放的荷载也相应增大, 使后开挖一侧隧洞的围岩位移和应力增大；开挖过程中应使左右洞的应力释放量尽量接近, 降低最终拱顶沉降和拱顶围压拉应力, 确保隧道围岩稳定及衬砌结构安全。

Comparative Analysis of Different Excavation Schemes for Asymmetric Double-Arch Tunnel

Based on the lining structure of asymmetric double-arch tunnels of an expressway, the corresponding finite element analysis model was established in terms of different conditions of ground surface(being flat, upward inclined and downward inclined). The stability of surrounding rock, safety of lining structure and bias pressure were selected as the performance indicator for tunnel stability. The impact of different excavation schemes on tunnel stability at different conditions of ground surface was comprehensively analyzed by digital simulation method. The results showed the different ground surface conditions would have a great influence on the stress and deformation of the surrounding rock and lining structure of asymmetric double-arch tunnels. Thus in the case of ground surface being flat, the larger hole should be excavated first. As for the inclined ground surface, the different inclination of ground surface and different span of two arches should be taken into account in the determination of excavation scheme. Furthermore, in the construction of asymmetric double-arch tunnel, the stress release of surrounding rock on the excavated side will cause vertical stress increased on the unexcavated side, resulting in an increased load release during the later excavation. Consequently the final settlement and stress of surrounding rock will all be increased. It is suggested that the stress release in the excavation of both holes shall be ensured to be close to each other, the final settlement and tensile stress of the surrounding rock at the arch crown shall be minimized so as to ensure the stability of surrounding rock and safety of lining structure.