大跨小净距偏压隧道施工方案优化分析

Analysis of Construction Schemes Optimization for Large-span Bias Tunnels with Small Clear Distance

在大跨小净距偏压隧道施工中,合理的施工方法和施工工序对保证围岩稳定性和支护结构受力有很大影响。结合大跨小净距偏压隧道的结构形式,总结了其受力特点,并建立大跨小净距隧道在Ⅴ级围岩浅埋偏压环境下的有限元数值模型,分别采用双侧壁导坑法、CRD法对不同施工工序下围岩位移、应力和塑性区等进行对比分析。结果表明:CRD对控制隧道水平收敛较为有利,但隧道拱脚处应力集中现象明显,围岩塑性区较大,双侧壁导坑法对控制隧道拱顶下沉较为有利;先开挖浅埋侧隧道时中岩柱两侧拱肩、拱腰应力集中较大,而先开挖深埋侧隧道时隧道拱脚应力集中较大;先开挖隧道内侧时,洞周围岩位移较大。

For the construction of large-span bias tunnel with small clear distance, rational excavating methods and sequence have important impacts on stability of surrounding rock mass and supporting optimization. Based on the structure type of large-span bias tunnel with small spacing, its mechanic characteristics are summarized. At the same time, numerical simulation models under Grade V are established and the displacement, stress, the plastic zone of surrounding rock under CRD and double side excavation method are analyzed and compared. The results show that CRD excavation method is propitious to control level convergence while double side excavation method is propitious to control settlement of crown. Displacement of surrounding rock is much bigger if tunnel＇s lateral is excavated before tunnel＇s outside. The stress of abutment and haunch between the middle rock pillar concentrated more seriously if the shallow tunnel is excavated earlier than the deep one, or the stress of arch springing of the tunnel concentrated more seriously.