嵌岩桩现场监测试验及负摩阻力优化计算研究

为了解决桩基负摩阻力所引起的桩体破坏、桩基不均匀沉降等工程问题,在桩周土体沉降及桩身应力应变现场监测试验的基础上,分析了嵌岩端承桩桩侧剪切变形与负摩阻力的关系,建立了嵌岩端承桩与周围土体剪切变形量的计算方法,对浅层位置处桩-土监测数据进行对比分析,同时考虑嵌岩端承桩周围土体竖向有效应力对剪切变形的影响,并对现有规范中嵌岩端承桩负摩阻力计算方法进行优化改进。结果表明:1)嵌岩端承桩桩顶在不受外力约束时,浅部桩-土剪切变形量为4～5 mm; 2)深层位置处桩-土剪切变形小于浅层桩-土剪切变形,负摩阻力的作用无法充分发挥;3)采用优化计算法所得负摩阻力值与现场监测试验结果吻合度较高,所得下拉荷载可以满足经济、安全设计要求。研究结果可为桩基工程的设计和安全施工提供参考。

Study on field monitoring test and negative friction optimization calculation of rock-socketed pile

In order to solve the engineering problems of the pile failure and uneven settlement caused by negative friction of pile foundation, the relationship between lateral shear deformation and negative friction of rock-socketed end-bearing pile was analyzed on the basis of field monitoring tests of soil settlement around piles and stress-strain of piles. The calculation method of shear deformation of rock-socketed end-bearing pile and surrounding soil was established, and the monitoring data of pile and soil at shallow position was compared and analyzed by using this method. At the same time, considering the influence of vertical effective stress around rock-socketed end-bearing pile on shear deformation, the calculation method of negative friction of rock-socketed end-bearing pile in the existing code was optimized and improved. The results show that: 1) when the top of rock-socketed end-bearing pile is not constrained by external force, the shearing deformation of shallow pile-soil is 4-5 mm; 2) the shear deformation of pile-soil at deep position is less than that of pile-soil at shallow position, and the role of negative friction can not be brought into full play; 3) the negative friction obtained by optimization method is in good agreement with the monitoring results of field test, and the obtained pull-down load can meet the requirements of economical and safe design. The research results can provide reference for the design and safe construction of pile foundation engineering.