基于门式抗浮框架的基坑开挖下卧隧道变形控制

Anti-Uplift Portal Frame in Control of Underlying Tunnel Deformation Induced by Foundation Pit Excavation

隧道上方基坑开挖卸载不可避免引发隧道上浮变形,门式抗浮框架作为一种抗浮措施,其抗浮机理尚不明确.以某隧道长距离共线基坑工程为依托,对门式抗浮框架施作过程以及基坑大面积开挖对下卧盾构隧道的影响进行数值模拟研究,探究门式抗浮框架与地层相互作用机制及抗浮效果,最终提出抗浮框架结构优化设计建议.结果表明:门式抗浮框架施作过程竖井开挖可引发隧道上浮变形,通过竖井跳挖及回填可有效控制其引起的隧道变形;基于门式抗浮框架的基坑开挖使隧道上浮量从无抗浮框架的19.5 mm减小至15 mm;抗浮板和抗拔桩连接处在基坑开挖阶段存在应力集中,属于结构薄弱部位,应做局部加强处理.

The excavation of foundation pit above the existing metro tunnel inevitably leads to the uplift of the tunnel. As an anti-uplift measure, the anti-uplift portal frame is still lack of research. Based on a foundation pit excavation project colinear with tunnel for long-distance, the excavation influence on the underlying shield tunnel during the construction process of anti-uplift portal frame and the foundation pit excavation was studied via numerical simulation. The interaction mechanism between the anti-uplift portal frame and ground as well as the anti-uplift effect were analyzed. Finally, a structural optimization design was proposed based on the simulation. The results show that the tunnel may be uplifted due to the shaft excavation during the construction of the anti-uplift portal frame and the uplift can be effectively restricted by backfilling and sectional excavation. Compared to the excavation without the anti-uplift portal frame, the uplift value of the tunnel decreases from 19.5 mm to 15 mm because of the restriction of the anti-uplift portal frame. The connection between the slabs and piles are weak positions of the structure due to the stress concentration and it is necessary to do a local reinforcement treatment in the connection.