浅埋暗挖隧道近距离平行上跨对既有盾构隧道的变形影响分析

Analysis of Deformation Impact of the Adjacent Over-crossing Parallel Tunnel Excavated by the Shallow Mining Method on the Existing Shield Tunnels

依托呼和浩特市浅埋暗挖隧道近距离平行上跨既有地铁2号线工程,通过有限元数值模拟和现场监测,对不同的开挖工法和反压措施进行方案比选,研究上穿施工引起盾构隧道结构上浮的变形规律。结果表明:在施工中采用砂袋反压可有效控制盾构隧道的变形,通过对比发现,第二次砂袋反压的竖向位移控制率明显低于第一次反压,故现场施工中应尽早对隧道进行砂袋反压,避免因反压时间较迟导致竖向位移控制率过小而无法达到良好的反压效果;上穿工程引起既有地铁2号线隧道的变形曲线呈“半抛物线”形,且随着新建隧道开挖卸荷而产生左右变换的现象;由于土体卸荷、覆土埋深较浅等因素,盾构管片发生不均匀变形,最终既有盾构隧道管片整体变形呈“竖鸭蛋”状;综合经济、效率等因素,最终确定的方案为CD法+双侧反压。该工程采用优化方案后,最终将盾构隧道道床最大上浮变形控制在2.51 mm,满足规范控制值4.0 mm要求。

Given that the tunnel excavated by the shallow mining method adjacently crossed over the existing Metro Line No.2 in a parallel way in Hohhot,the scheme comparison was carried out for different excavation methods and counter-pressure measures by means of finite element numerical simulation and on-site monitoring,and the study was conducted on the floating deformation pattern of shield tunnel structure caused by over-crossing construction.The results showed that the use of sandbags for counterpressure during construction could effectively control the deformation of shield tunnels,and through comparison,it has been found that the vertical displacement control rate of the second sandbag counterpressure was significantly lower than that of the first sandbag counterpressure.So,sandbag counterpressure for tunnels should be conducted during on-site construction as early as possible to avoid a smaller vertical displacement control rate caused by delayed counterpressure,which would further lead to a failure to realize a good effect of counterpressure.It has also been found that the curve of tunnel deformation of Metro Line No.2 caused by the over-crossing works was of a"semi-parabolic"shape,and the phenomenon of left-right conversion occurred with the excavation and unloading of the new tunnel.Besides,unhomogeneous deformation occurred in shield tunnel segments due to various factors,such as soil unloading,shallow depth of overburden,etc.and the overall deformation of the existing shield tunnel segments was of a"vertical duck egg"shape.The finalized scheme of the Works was CD method+two-sided counterpressure based on economical factor,efficiency and other factors.After the optimization scheme was adopted in the Works,the maximum floating deformation of the shield tunnel roadbed was finally controlled at 2.51 mm,which complied with the specified control value,i.e.4.0 mm.