地铁双洞单线盾构隧道下穿引起既有铁路沉降实测研究

Field Measurement of Existing Railway Settlement Induced by Subway Double-Tube Single-Track Shield Tunnel Under-Passing

为揭示北京卵石土地区双洞单线隧道下穿施工期对既有铁路的沉降影响,基于某地铁下穿有砟铁路工程,以精密电子水准仪和自动化静力水准仪对铁路沉降开展现场实测,并对监测数据的时空规律进行挖掘分析,对左右线影响的空间叠加效应、地面沉降随盾构推进的时间台阶效应、道砟层和线路加固体系对沉降的隔离效应开展研究。结果表明,路基和轨道最大沉降发生在左右线隧道中心对应位置,隧道左线、右线先后下穿过程对铁路的沉降影响有明显叠加效应;路基和轨道沉降影响为突变型,可划分为左线刀盘切土及推进、左线盾尾离开、右线刀盘切土及推进、右线盾尾离开4个阶段,时程曲线台阶特征明显,施工期应密切关注;路基和轨道沉降影响在下穿施工期基本发展完成,该阶段沉降量占最终总沉降量88%以上,随后逐渐收敛;下穿施工引起既有铁路轨道沉降最大值为18.94 mm;引起既有铁路路基沉降最大值为24.24 mm,轨道沉降曲线较路基沉降曲线更为平缓,铁路道砟层和3-5-3扣轨起到有效隔离作用。

Based on a subway project with a ballasted railway,the on-site measurement of the railway settlement was carried out with electronic precision level and automatic HLS,to reveal the impact on the settlement of the existing railway during the construction period of the Double-tube Single-track shield tunnel tunnel in the Pebble Land Area of Beijing.The temporal and spatial laws of monitoring data were excavated and analyzed,and the spatial superposition effect of the influence of the left and right lines,the time step effect of the ground subsidence with the advancement of the shield,and the isolation effect of the ballast layer and the line reinforcement system on the subsidence were studied.The maximum settlements of subgrade and tracks were found at positions corresponding to the tunnel centres of the left and right lines,and the under-passing processes of both lines had distinct-phased superposition effects on the railway settlements.The abrupt settlement influence of subgrades and tracks could be divided into four stages,which are the left-line shield cutting and propelling,left-line shield tail off,right-line shield cutting and propelling and right-line shield tail off.Considerable attention should be devoted to the time-history curve during construction due to its evident step characteristics.Furthermore,the settlement influence of subgrades and tracks was mainly within the construction period,accounting for>88%of the final settlement.Afterward,the settlement gradually converged.The maximum settlements of the existing railway tracks and subgrades caused by under-passing construction were 18.94 and 24.24 mm,respectively.Additionally,the settlement curve of tracks was smoother than that of subgrades.The ballasted layer of the railway and 3-5-3 track-locking were essential for effective isolation of settlement.