基坑开挖对既有小直径桥墩的影响分析及加固设计

Influence of Foundation Pit Excavation on Existing Small Diameter Piers and Reinforcement Design

温州市某主干道采用U型槽下穿高速公路桥梁。U型槽基坑开挖改变了既有小直径桥墩的受力状态,并对桥梁结构安全造成影响。针对该情况,采用有限元数值分析,并结合实验室土工试验,对U型槽基坑开挖各个工况下小直径桥墩位移和内力进行力学分析。分析结果表明:基坑开挖导致桩基附加弯矩增大,桥墩发生较大横向位移,裂缝宽度达0.18 mm。根据受力分析结果,对既有小直径桥墩进行加固设计。桥墩加固后进行基坑开挖,减小了桥墩横向位移,附加弯矩降低,裂缝减少至0.07 mm,桥墩稳定性安全系数得到提高。通过施工监测数据和数值计算结果的对比,计算分析值与实测值基本吻合。本文工作可作为同类型小直径桥墩全周围基坑开挖结构分析与加固设计的借鉴。

The underpass with U-shape groove’s structure goes through an existing highway bridge as a main road in Wenzhou. The excavation changed the stress state of the existing small-diameter pier and affected thesafety of bridge structure. Thus the displacement and internal force of small-diameter pier under various workingconditions in process of U-shape groove excavation were numerically analyzed with finite element method combined with the laboratory test. The results exhibit that the additional bending moment of pile increases,andthe transverse displacement of pier also increases with the crack width of 0.18 mm due to the excavation. The cosolidation design of existing small-diameter pier was carried out according to the results of force analysis.When the bridge pier is cosolidated prior to the excavation,the transverse displacement and additional bendingmoment of the pier reduce and the crack of pier decreases to 0.07 mm,improving the stability safety factor ofbridge piers. The numerical simulation results are generally consistent with the monitoring data duringconstruction. This paper can give a reference for structural analysis and reinforcement design of the same type of small-diameter pier with the surrounding excavation.