黄土地区地铁双连拱隧道浅埋暗挖施工变形特征研究——以西安地铁5号线停车场出入场线工程为例

Research on Deformation Characteristics of Shallow-buried Mined Double-arch Metro Tunnel in Loess Area:a Case Study on Parking Lot Entrance and Exit Line Project of Xi′an Metro Line No.5

为研究黄土地区城市地铁双连拱隧道施工变形特性,依托于西安市地铁5号线停车场出入场线浅埋暗挖双连拱隧道工程,通过对现场监测数据的分析,从地表沉降、新建隧道拱顶沉降及超邻近既有隧道的拱腰收敛变化规律3个方面进行探讨。研究发现:1)施工过程中最大地表沉降为19.66 mm,最大沉降速率为2.31 mm/d,皆小于施工控制限值;2)对于超浅埋隧道,施工不确定性、土层不均匀性、土体各向异性、地表随机荷载等干扰因素会明显影响到地表沉降曲线的形状,进而可能使得Peck公式对地表沉降预测结果与实测值存在较大偏差;3)地表沉降达到稳定状态时,掌子面与监测断面距离明显超过5倍洞径,而初期支护变形速率较快,达到稳定阶段时对应距离基本在3~5倍洞径;4)受中导洞阻隔作用,后行洞施工对先行洞初期支护的应力变化及收敛变形等影响并不明显;5)正洞掌子面与监测断面的距离大于2倍洞径后,既有隧道拱腰收敛基本趋于稳定,各监测断面处最终拱腰收敛值基本在4 mm以内。

Based on the shallow-buried mined double-arch tunnel project applied in parking lot of Xi′an Metro Line No.5,the deformation characteristics of double-arch metro tunnel in loess area are studied.The variation rules of surface settlement,lining deformation of new tunnel and hance convergence of super-adjacent existing tunnel are analyzed through field monitoring data.The results show that:(1)In the construction,the maximum surface settlement is 19.66 mm and the maximum settlement rate is 2.31 mm/d,both of which are less than the construction control limit.(2)For ultra-shallow buried tunnels,influencing factors such as construction uncertainty,soil heterogeneity,soil anisotropy,surface random load,etc.will obviously affect the shape of the surface settlement curves,which may make the Peck formula have a large deviation from the predicted results of the surface settlement.(3)When the surface settlement reaches a stable state,the distance between the tunnel surface and the monitored section is obviously more than 5 times of the tunnel diameter,while the primary support deformation rate is faster,and the corresponding distance is basically 3~5 times of the tunnel diameter when the surface settlement reaches a stable state.(4)Due to the barrier effect of the middle pilot hole,the effect of the construction of the back tunnel on the stress variation and convergent deformation of the primary support of the first tunnel is not obvious.(5)When the distance between the tunnel face and the monitored section is more than 2 times of the tunnel diameter,the convergence of the hance of the existing tunnel basically tends to be stable,and the final convergence value of the hance at all monitored sections is basically within 4 mm.