砂泥岩地层双线盾构隧道近距侧穿铁路桥桩基施工优化分析

Construction Optimization Analysis of Double⁃line Shield Tunnel with Short⁃distance Side⁃passing Railway Bridge Piles in Sand⁃mudstone Stratum

依托成都轨道交通13号线三公区间中间风井—公园大道站盾构区间工程,针对该区间长距离穿越砂泥岩地层且近距离侧穿铁路桥,提出了堆焊螺旋输送机钢板块、降低刀盘转速、控制盾构匀速穿越不停机等技术措施,并利用FLAC3D有限元软件,以桩基侧向变形、沿隧道纵向弯矩与地表位移为分析指标,展开对区间隧道开挖顺序与加固措施的优化研究。结果表明:对于单根桩基而言,其侧向变形量在先开挖双线隧道中距离该桩基更近的隧道时更危险,位于两隧道一侧桩基的弯矩亦受靠近隧道先行开挖的影响最大,但施工顺序对两隧道间桩基的弯矩影响较小;相较于单措施加固,注浆+隔离桩双措施加固能协同改善地表不利沉降与隧道间夹岩隆起现象。基于施工优化结果,本工程砂泥岩地层双线盾构隧道采用先右后左的开挖顺序与注浆+隔离桩的综合加固方案,桥墩各项位移现场监测值均未超过预警指标,实际控制效果良好。

Relying on the shield tunnel project of Chengdu Rail Transit Line 13 from the middle wind shaft of the Sangong section to Park Avenue Station,for the long-distance crossing of sand-mudstone stratum and the short-distance side crossing of railway bridges in this section,the paper proposed technical measures such as installing steel blocks of screw conveyors,reducing the speed of cutterhead,and controlling the shield tunnel to cross at a uniform speed without stopping.Using FLAC3D finite element software,taking the lateral deformation of the pile foundation,the longitudinal bending moment along the tunnel and the surface displacement as the analysis indicators,the optimization research on the excavation sequence and reinforcement measures of the interval tunnel was carried out.The results show that,for a single pile foundation,its lateral deformation is more dangerous when excavating the tunnel closer to the pile foundation in the double-track tunnel first,and the bending moment of the pile foundation on one side of the two tunnels follows the same law.But the construction sequence has little effect on the bending moment of the pile foundation between the two tunnels.Compared with the single-measure reinforcement,the grouting+isolation pile dual-measure reinforcement can synergistically improve the unfavorable settlement of the surface and the middle rock uplift phenomenon between the tunnels.Based on the results of construction optimization,the double-line shield tunnel in the sand-mudstone stratum of this project adopted the excavation sequence of right first and then left and the comprehensive reinforcement scheme of grouting+isolation pile.The on-site monitoring values of various displacements of the bridge piers did not exceed the early warning indicators,and the actual control effect was good.