饱和黄土区地铁隧道穿越桥梁桩基托换技术研究

在城市轨道交通中,地下工程往往需要穿越上部建筑物,为了保证建筑物安全正常使用,托换技术已成为解决城市建设施工的一种有效方法。在饱和黄土地区,由于黄土特殊的工程性质,桩基托换工程实例相对较少。以兰州市轨道交通1号线地铁隧道下穿既有市政桥梁为工程背景,详细介绍桩基托换设计方案,并建立三维有限元模型,进行数值分析。研究隧道开挖和切桩过程中地表沉降、桩基沉降和托换桩基受力机制,验证托换方案的可行性。研究结果表明:地表最大沉降为10.5 mm,桩基最大沉降量为9.7 mm,相邻桩基沉降差最大值为2.2 mm,满足相关规范要求。托换后桩底轴力为1 143.9 k N,小于单桩设计承载力4 739 k N,在初始阶段、新增承台及桩基、切除左右隧道内桩基及最后阶段衬砌左右隧道,托换桩基承载力均满足要求。

Research on Technology of Metro Tunnel Crossing Bridge Pile Foundation Underpinning in Saturated Loess District

During urban rail transit engineering,the underground works need to underpass structures on the ground. In order to ensure the safety and normal service of the buildings,underpinning has become an effective way in urban engineering,but there is only a few such engineering practice due to unique properties of the loess. Based on the engineering of railway tunnel crossing existed municipal bridge of Lanzhou rail transit line 1,pile foundation underpinning design scheme is introduced in detail and the three-dimensional finite element model is established to conduct numerical analysis. The surface subsidence,settlement of pile foundation,and force mechanism of pile foundation underpinning are studied in the process of tunnel excavation and cutting stakes to verify the feasibility of the underpinning program. Research results show that the maximum ground settlement is 10. 5 mm,the maximum pile foundation settlement is 9. 7 mm and the maximum settlement difference between the adjacent pile foundations is 2. 2 mm,which satisfy the requirements of relevant specifications. The pile axial force is1 143. 9 k N after underpinning,less than the designed bearing capacity 4 739 k N for a single pile. The underpinning pile foundation bearing capacities,measured in the initial stage,when new caps and pile foundations are added,pile foundations are cut off in the left and right tunnels and the final tunnel lining is applied,all meet specifications.