富水砂-黏复合地层大断面暗挖隧道施工力学行为

Construction Mechanical Behavior of Large Cross-section Undercut Tunnel in Water-rich Sand-Viscose Composite Stratum

富水砂-黏复合地层暗挖施工极易诱发地表及支护结构变形过大等复杂问题。以北京地铁17号线某交叉中隔壁(cross center diaphragm, CRD)法施工隧道工程为依托,对施工过程中的地表沉降、孔隙水压力、围岩压力、初支内力等进行现场监测后,得到了各监测对象的变化规律和总体分布。研究结果表明:新建隧道暗挖施工引起的地表沉降值较大,拱顶沉降与导洞收敛变形速率与变形量虽符合设计要求,但稳定值接近限值,富余量小;稳定后的孔隙水压力值较小,约为5 kPa,与地勘水头高度基本一致;由于先行标准线开挖的影响,新建隧道围岩压力呈现左右不对称分布的现象,围岩压力沿洞周呈现出拱底→拱腰→拱脚→拱顶→拱肩依次减小的分布规律;稳定后的钢筋应力沿洞周分布形式与围岩压力基本一致,其最大值出现在左侧拱腰处。基于上述研究,研究成果可为同类型富水砂-黏复合地层的暗挖隧道设计和施工提供一定的借鉴。

It is easy to induce complex problems such as excessive deformation of surface and support structure by underground excavation in water-rich sand-viscose composite stratum.Based on a cross center diaphragm(CRD)tunnel construction project of Beijing metro line 17,after on-site monitoring of surface settlement,pore water pressure,surrounding rock pressure and internal force of primary branch during construction process,the change law and overall situation of each monitoring object were obtained.The results show that the surface settlement caused by the concealed excavation construction of the new tunnel is large.Although the vault settlement and the convergent deformation rate and the amount of deformation of the pilot tunnel meet the design requirements,the stability value is close to the limit and the surplus is small.The pore water pressure after stabilization is small,about 5 kPa,which is basically consistent with the height of geological exploration head.Due to the influence of the excavation of the advanced standard line,the surrounding rock pressure of the new tunnel presents the phenomenon of asymmetric distribution from left to right,and the surrounding rock pressure decreases in turn along the tunnel circumference in the order of arch bottom→arch waist→arch foot→arch top→arch shoulder.The distribution of reinforced stress along the tunnel after stabilization is basically consistent with the surrounding rock pressure,and its maximum value appears at the left arch waist.Based on the above research,the results of research can provide a certain reference for the design and construction of undercut tunnels in the same type of water-rich sand-viscous composite stratum.