土压平衡盾构近距离下穿既有地铁无配筋二次衬砌大断面隧道施工技术

Construction Technology of Earth-Pressure Balance-Shield Crossing Underneath Existing Large-Cross-Section Metro Tunnel with Unreinforced Secondary Lining

为确保盾构近距离下穿北京地铁1号线复兴门—西单区间无配筋二次衬砌大断面隧道期间结构、设施稳定,变形可控,列车运营不受影响,结合工程实际调研情况,根据穿越区段隧道状态评定为3级(较重病害)的结果,提出盾构近距离下穿大断面素混凝土二次衬砌隧道关键施工技术,主要包括1号线结构病害治理、粘贴芳纶布、钢板带加固,1号线洞外注浆加固穿越段地层,盾构掘进参数控制,并辅以监控量测技术。结果表明:1)1号线隧道无配筋结构采用芳纶布、钢板带等加固技术,强度、刚度、稳定性等均满足要求,未发生结构开裂及掉块情况。2)盾构与既有线之间采用施工导洞密贴穿越1号线后两侧注浆,能有效减少钻孔长度,提高钻孔及注浆的精确性,同时密贴导洞为1号线提供有效支顶作用;另外,导洞下穿段设置千斤顶支顶措施,可提高沉降控制效果。3)设置试验段、优化掘进参数、充填克泥效、同步及二次注浆等措施,在沉降控制中起到了十分积极的作用,减小了对既有线和列车的影响,保证了施工安全和质量。

A shield tunnel is being constructed closely crossing underneath the Fuxingmen-Xidan large-cross-section tunnel of Beijing Metro Line 1 with unreinforced secondary lining.As such,to ensure the stability of structures and facilities,controllable deformations,and normal operation of trains during the construction of the shield tunnel,the overall condition of the undercross section is assessed as Grade 3(serious disease)based on the current situation.Moreover,key construction technologies related to shield tunneling through large-cross-section tunnels with plain concrete secondary linings are proposed herein.These technologies involve structural-damage control with respect to the Line 1,aramid fiber-based adhesion,steel plate-belt reinforcement,grouting reinforcement outside the tunnel of Line 1,shield tunneling-parameter control,and monitoring and measurement.The following conclusions can be drawn from the obtained results.(1)The strength,stiffness,and stability of the unreinforced structure after reinforcement using aramid fibers and steel plate meet the requirements,and no structural cracking or block dropping occurs.(2)Undertaking grouting on both sides of the section of the shield tunnel near the crossing on the existing line through the guide tunnel can effectively reduce the drilling hole length and improve drilling and grouting accuracies.In addition,the guide tunnel provides effective support for Line 1.Furthermore,the jack supporting measure is set in the lower passing section of the guide tunnel to improve the settlement-control effect.(3)The setting of the test section,optimization of the tunneling parameters,filling of the clay shock,and synchronous and secondary grouting have substantially positive settlementcontrol effects,thus reducing the impact of the construction work on the existing line and operation of trains and ensuring safety and satisfactory quality with respect to the construction.