不平衡受力环境下钢管桩围堰结构研究与分析

Research and Analysis of Steel Pipe Pile Cofferdam Structure Under Unbalanced Force Environment

以京台高速公路齐河至济南段改扩建工程主桥P3号墩为研究背景,该工程深基坑处于黄河岸边,具有下游回水冲刷较大、距离已有桥墩基础非常近、承受不平衡水土压力作用的特点,围堰施工难度大,极易导致临近桥梁、围堰变形过大等安全问题的发生。针对工程实例,结合不平衡受力的特点,探索了钢管桩围堰支护的作用机理。通过对工程实例进行有限元建模分析,对钢管桩围堰、支撑结构的变形、强度进行分析,并对临近既有桥梁的沉降影响做了进一步分析。将有限元计算结果与实际监测数据进行对比,验证了有限元模型的合理性。结果表明:钢管桩围堰随施工的进行变形逐渐增大,变形主要集中在水土分界处,且背水面变形大于迎水面,最大变形呈现在第5分析步(施工承台结构阶段),变形值为30.40mm,位于短边水中面;支撑结构在长边左右两侧受力不均较明显,尤其在第2分析步(安装上层支撑结构阶段),最大受力发生在第4分析步(土体开挖至基坑底部阶段),最不利截面强度验算为121.47MPa<215MPa,满足要求。临近的既有桥梁最大沉降值和最大倾斜度均满足规范要求。

Taking the P3 pier of the main bridge of the reconstruction and expansion project from Qihe to Jinan section of the Beijing-Taipei Expressway as the research background,the deep foundation excavation is located on the bank of the Yellow River.It has such characteristics as large backwater erosion in the downstream,being very close to the existing pier foundation,and bearing unbalanced water and soil pressure.The construction of cofferdams is difficult,which is likely to lead to the occurrence of safety problems such as excessive deformation of adjacent bridges and cofferdams.In view of the engineering example,combined with the characteristics of unbalanced force,the mechanism of steel pipe pile cofferdam support is explored.Through the finite element modeling analysis of the engineering example,the deformation and strength of the steel pipe pile cofferdam and the supporting structure are analyzed,and the influence of the adjacent existing bridge settlement is further analyzed.The finite element calculation results are compared with the actual monitoring data to verify the rationality of the finite element model.The results show that the deformation of the steel pipe pile cofferdam increases gradually with construction.The deformation is mainly concentrated at the water-soil boundary,and the deformation of the downstream face is greater than that of the upstream face.The maximum deformation is presented in the fifth analysis step(construction pile cap structure stage),and the deformation value is 30.40mm,which is located on the short side of the water surface.The support structure has obvious uneven stress on the left and right sides of the long side,especially in the second analysis step(the stage of installing the upper support structure).The maximum stress occurs in the fourth analysis step(the stage of soil excavation to the bottom of the foundation excavation),and the strength of the most unfavorable section is calculated to be 121.47MPa<215MPa,which meets the requirements.The maximum settlement value and maximum inclination of the adjacent existing bridge meet the requirements of the specification.