近接施工上覆既有车站变形动态反分析及预测

Dynamic Back-Analysis and Prediction of Overlying Subway Station Displacement Induced by Approaching Excavation

北京地铁新建4号线宣武门站分离式双洞隧道近距离垂直下穿既有2号线车站，是4号线全线建设的控制性工程。为保证施工顺利进行，需对施工引起的既有车站变形做出合理预测。为此，引入位移反分析方法，依据施工计划建立模拟动态施工过程的有限元模型，根据试验段确定“反分析前两个施T步既有车站的实测位移，确定计算参数，进而预测下一施工步既有车站变形”的动态位移反分析预测方案，对剩余施工步序中既有车站的变形进行预测及分析。采用该方法预测既有车站最大变形的误差为0-2．16mm，预测最大差异沉降的误差为0．12～2．59mm，比正分析方法预测准确；同时．该方法的预测准确性受新建隧道施工方法的影响，在前后两个施工步施工方案相似的情况下．预测准确度高，反之则会相应地降低。

The separated double-tube tunnel of the Xuanwumen station passes vertically beneath an existing station of the Beijing Metro Line 2. To ensure smooth construction, deformation of the existing station needs to be predicted properly. In order to do this, a displacement back-analysis is introduced, and a finite-element model for the dynamic simulation of the construction process is set up. Calculation parameters are determined based on the measured displacement in previous construction steps of the trial section, then the station deformation in the next construction step is predicted by back analysis. The method shows that： the back-analysis is more accurate than the direct analysis, with a maximum deformation error of 0-2.16ram and a maximum differential settlement error of 0.12-2.59mm; its prediction accuracy is influenced by the approaching construction method; and in a case where construction schemes for the previous and subsequent construction steps are similar, the prediction is more accurate.