浅埋暗挖隧道近距下穿既有地铁的关键技术

 主要针对越来越多的浅埋暗挖隧道近距下穿既有地铁工程，结合北京地铁5号线崇文门站下穿既有地铁2号线区间隧道工程，介绍新建浅埋暗挖隧道近距下穿既有地铁隧道的关键控制技术。主要包括：对既有地铁的现状进行全面调查评估；根据现状评估结果并结合理论分析和类似工程经验确定既有地铁的变形控制标准；通过有限元分析方法等进行新建隧道施工对既有地铁影响的预测分析；对主要施工方案进行优化，并选取超前大管幕、掌子面注浆、补偿注浆等辅助措施；根据数值分析结果并结合既有工程经验，将主要控制标准按施工步序进行分解，实施控制标准的分阶段控制；通过远程实时监控系统即时监测和分析既有地铁的动态变化，对出现的结构开裂、沉降过大等异常情况及时采取灌浆加固、注浆抬升等处理措施，确保既有地铁的正常安全运营。

KEY TECHNIQUES ON SHALLOW EMBEDDED TUNNEL CONSTRUCTED BENEATH EXISTING SUBWAY TUNNEL

With respect to more and more shallow embedded tunnel constructed beneath existing subway tunnel，the effects of shallow embedded tunnel construction on existing subway tunnel are discussed；and some key control techniques used successfully in Chongwenmen station of Beijing metro line No.5 constructed beneath existing tunnel of metro line No.2 are presented. A comprehensive survey of the existing subway tunnel has been performed before the tunnel construction. Based on the survey results，the deformation control indexes and their allowable values are identified in the light of theoretical analyses and similar engineer experiences. The finite element method combined with experience and judgment is recommended to predict the effects of tunneling on the existing subway. The more suitable excavation construction methods and auxiliary measures such as big steel pipes，face grouting reinforcement and compensation grouting are selected by various comparison analyses. On the basis of numerical analyses and similar engineer experiences，the allowable value of the main deformation control index is controlled according to construction steps. A system of remote real-time monitoring is used to monitor dynamic responses of the existing subway；and the measured data were back analyzed immediately. When abnormal issues are found，protective measures are adopted in time to ensure safety running of the existing subway. For example，control compaction grouting is adopted to heave up the existing tunnel structures in the case，and the maximum upheaval of the existing tunnel reaches 16 mm.