新建地铁隧道“零距离”下穿既有车站施工技术分析

Anaysis of Construction Techniques for a Metro Tunnel Approaching an Existing Station

新建地铁隧道"零距离"下穿既有运营地铁车站结构的施工将引起既有车站结构的变形,影响既有地铁正常运营。文章以北京地铁7号线下穿既有10号线双井站为工程背景,针对地铁区间隧道"零距离"穿越既有车站全断面开挖、台阶法开挖及CRD法开挖引起的既有车站主体结构、既有10号线轨道及区间隧道支护结构等的变形和受力状态进行了数值模拟,对比分析了不同开挖方案引起的既有车站结构及轨道的变形特性;以既有线轨道的变形量为控制标准,结合施工引起既有车站结构的受力变化,确定了区间隧道"零距离"下穿既有车站的施工开挖方案;同时对采用CRD法施工时的不同加固措施对既有车站及轨道变形的控制效果进行了数值模拟分析,确定了施工中地层加固范围及加固长度等注浆加固参数。现场监测分析结果表明,基于数值模拟分析优化并实施的区间隧道交叉中隔壁法(CRD)开挖方案以及在左右线隧道间的夹土层、隧道掌子面地层及隧道左右外轮廓3 m内地层进行加固的施工技术方案保证了既有线轨道变形速率不大于0.04 mm/d和既有车站主体结构累计变形量小于10 mm的要求。

Construction of a new metro tunnel approaching an existing metro station may cause deformation of the station structure, affecting normal operation of the metro. Based on Beijing Metro Line 7 passing under the Shuangjing Station of the existing Beijing Metro Line 10, a numerical simulation was carried out regarding the deformation and force applied to the station＇s main structure, the metro track support of the running tunnel due to full-face tunnel excavation, and the bench method excavation and CRD excavation of the metro running tunnel approaching the existing station. A eontrastive analysis was undertaken regarding the deformation characteristics of the existing station and track under different excavation schemes, and an excavation scheme was determined for the running tunnel approaching the existing station considering deformation control and force variation factors. A numerical simulation was performed aimed at the reinforcement effect for deformation control of the existing station and track under different reinforcement measures when the CRD method was used, and parameters of grouting reinforcement were determined, such as reinforcement scope and length. Analysis of site monitoring results shows that the optimized CRD construction method and reinforcement measures, such as reinforcing the interbed between the left line and right line, the stratum at the working face, and the area within 3m outside the left and right external contour, can guarantee the safety of the existing station. The deformation rate of the existing track is no more than 0.04 mm/d and the accumulated deformation of the main structure of the existing station is less than 10mm.