浅埋暗挖隧道施工性态的数值模拟与分析

地铁隧道施工中,隧道开挖程序、施作的步骤对隧道稳定性及地表沉降影响显著。北京地铁10号线某标段浅埋单洞双层隧道,是出入口通道与车站中洞、旁边单层侧洞相接的暗挖部分,单、双层转换,初支结构形式和施工都很复杂。目前国内外对单洞双层隧道分析较少,与车站和通道相连接的这种单洞双层隧道比较短,对它的分析往往被忽视。对采用3层6导洞的CRD工法施工的这种浅埋单洞双层隧道的施工性态进行数值模拟,分析该区域隧道施工引起的地表沉降,探索一次性开挖成洞及隧道分步开挖引起的地表沉降槽的变化形态,拱顶沉降及拱顶主应力的变化规律。数值分析表明:施工工序不同使隧道的偏挖引起的沉降槽向未开挖一侧偏移,此过程中地层最大沉降并不发生在隧道中线处,而是完成全部开挖,地层变形稳定后,其累计沉降最大值位于隧道中线处。隧道开挖衬砌完全施作后,地表沉降变化不大,但是后续开挖步引起的结构内力应予以重视,尤其对于中隔壁支撑及拱底衬砌的支护,要及时施作拱底二次衬砌。研究结果为单洞双层隧道分步施工控制地表变形和洞周位移提供参考依据。

Numerical simulation and analysis of construction behavior of shallow tunneling by excavation

In the construction of subway tunnels,the process of tunnel excavation and construction procedure has a profound influence on the tunnel stability and subsidence of the ground surfaces.In Beijing Metro Line10,one section of the tunnel,connecting between the metro station and a side tunnel,has a single opening transformed from one passage to two.This in turn causes considerable complications in construction and the analyst has very little experience in dealing with such situation.In the present paper,numerical simulation was performed to investigate the construction behavior using a CRD method.The analyses included special features such as the ground subsidence resulting from tunnel construction,different forms of settlement trough caused by one-step or step-by-step tunneling method,settlement of the vault and change of the stress field in the vault.Numerical results indicate that the settlement trough tends to deflect sideway towards unexcavated areas due to different construction schedules.After all the excavation is completed and the ground settlement has become stabilized,the accumulated maximum subsidence occurs at the center line of the tunnel.There is only little movement to ground subsidence after all the liners are in place.However,special attention should be given to the stresses caused by subsequent excavation.In this case,secondary liners must be provided to support the mid-walls and vault bottoms.The study provides a reference to control the ground settlement and convergence of tunnel inner perimeter in contruction of tunnels composed of a single opening with two passages.