地铁车站拱盖法施工沉降监测分析及控制对策

青岛地铁3号线中山公园站位于土岩复合地层中,采用拱盖法施工,车站开挖最深约27.24 m,上层为第四系强风化花岗岩,下部为中微风化花岗岩、花岗斑岩。局部强风化厚度大,中、微风化岩面局部较陡峭,岩层接触部位易失稳。为使开挖工程顺利进行,对开挖过程地表沉降进行监测分析。结果表明:采用拱盖法施工时,导洞掌子面施工至监测断面前方20 m左右时开始出现沉降;随着掌子面与监测断面距离的减少,沉降速率不断增加;掌子面下穿监测断面时,一般沉降量为7～15 mm;穿过监测断面5～10 m时,监测点沉降速率达到最大;穿过监测断面10 m后,沉降速率开始下降;穿过监测断面20 m后,大部分监测点趋于稳定。为保证支护起到良好的控制地表沉降的作用,初期支护应在开挖后立即施作,并尽早闭合。此外,左、右导洞在开挖过程中会相互产生较大的沉降影响,监测发现左、右导洞开挖间距在2.5倍洞径左右为宜。通过监测分析,提出一系列控制对策,实践证明,这些措施是可行且有效的。

MONITORING AND ANALYSIS OF EXCAVATION-INDUCED SUBSIDENCE OF SUBWAY STATION CONSTRUCTED BY ARCH COVER METHOD AND CONTROL MEASURES

Zhongshan Park Station of Qingdao subway line No.3,which is constructed by arch cover method,locates in soil-rock composite layer.The maximal excavation depth is about 27.24 m.Upper overburden is composed of quaternary and highly weathered granite,and the lower part is consisted of medium-slightly weathered granite and granite-porphyry.The thickness of partially highly weathered rock layer is large and the medium-slightly weathered rock surface is partly steep,which makes the contact surface unstable.To ensure the excavation work,the ground subsidence was monitored and analyzed at the station.Results indicate that the subsidence emerges before the tunnel working face reaches to about 20 m in front of monitoring sections when the arch cover method was adopted.With the decrease of distance between the tunnel working face and monitoring sections,the subsidence velocity continues to increase.Generally,the value of subsidence is 7–15 mm when the excavation face was going through the monitoring sections.The velocity of ground subsidence increases to the maximum until the working face passes through the monitoring sections for 5–10 m.After the working face passes through the monitoring section for more than 10 m,the subsidence velocity begins to fall.Most of observation points have the trend to be stable after the working face passes through the monitoring sections for about 20 m.Supporting should be exerted and closed as early as possible to make sure that the supporting can play a good role.In addition,there is a interrelationship between the left and right pilot tunnels.It is indicated that the appropriate distance between the left and right pilot tunnels should be 2.5 times of the diameter of pilot tunnel.According to the monitoring and analysis results,a series of control measures are put forward,which are proved to be feasible and effective by practice.