暗挖隧道下穿跨河桥部分桥桩的影响分析及对策——以北京地铁14号线北工大站-平乐园站区间为例

为研究在不降水情况下暗挖隧道下穿跨河桥桥桩的影响并确定设计与施工方案，以北京地铁14号线北工大站-平乐园站区间(以下简称北-平区间)为例，根据暗挖隧道下穿桥桩后结构变形特点建立有限元模型，进行计算分析后进一步细化设计方案（暗挖断面架设临时仰拱）； 采用全断面深孔注浆对土体进行预加固，同时兼做堵水措施。施工过程中对桥桩变形进行全过程监测，并与有限元模型计算结果进行对比。目前该隧道已经通过竣工验收，桥梁结构稳定，最终变形收敛至稳定值。结果表明： 暗挖隧道通过架设临时仰拱+注浆堵水下穿桥桩是可行的； 有限元模型可预测隧道下穿桥桩的变形，可为今后类似工程提供参考。

Analysis on and Countermeasures for Mining Tunneling of Line 14 of Beijing Metro Crossing Underneath Existing Bridge Piles

Bei Ping running tunnel of Line 14 of Beijing Metro, which is excavated by mining method, crosses underneath the piles of an existing bridge. However, dewatering cannot be made to facilitate the excavation of the tunnel. In the paper, 2D finite element model is established and analysis is made on the structural deformation of the bridge, so as to study the influence of the tunneling on the existing bridge and to determine the design and construction scheme of the tunneling. The following countermeasures are taken according to the analysis results: temporary invert is installed for the mined tunnel; full face deep hole grouting is made to consolidate the ground in advance and to seal the ground water; full course monitoring is made for the bridge piles during the tunneling, and the monitoring results are compared with the results calculated by finite element model. So far, the tunnel has passed the as built acceptance, and the bridge keeps stable. Conclusions drawn are as follows: 1) The tunneling can cross underneath the existing bridges successfully after temporary invert is installed and grouting is performed; 2) The settlement of the existing piles can be predicted by means of finite element model.