基坑开挖对坑底工程桩性能影响参数分析*
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（1 滨海土木工程结构与安全教育部重点实验室（天津大学）， 天津 300072；2 天津大学建筑工程学院， 天津 300072； 3 天津市地下铁道集团有限公司， 天津 300051）
［摘要］基坑开挖对坑内工程桩的影响不可忽视。基于工程试桩实测资料验证的有限元参数，对不同基坑开挖深度及平面尺寸条件下坑底不同位置处单桩的工作特性进行参数分析。分析表明，基坑开挖导致较大的桩身初始拉力，桩身最大初始拉力值可达到将近地面试桩承载力的50%，桩身最大相对初始拉力随着基坑开挖宽度（B）与开挖深度（H）的比值增大而增大；当桩长（L）与基坑开挖深度（H）的比值为2～3时，桩身最大相对初始拉力出现最大值。桩身最大初始拉力相对位置基本上随L/H增加而减小，随B/H增加而增加。单桩刚度大多有所降低，最严重时可减小到原来的26.4%，对于L/H和B/H均较小的情况，相对刚度可能出现大于1的情况。基坑开挖引起的桩身最大初始拉力及其所在位置和单桩刚度的降低在设计中应加以考虑。［关键词］基坑开挖; 单桩; 桩身初始拉力; 相对刚度; 参数分析中图分类号：TU473.1 文献标识码：A 文章编号：1002-848X(2015)21-0063-07
Parametric analysis on influence of foundation pit excavation on the performance of pit bottom pilesZheng Gang1,2, Wang Qi1,2, Zhang Liming3(1 Key Laboratory of Coast Civil Structure Safety (Tianjin University), Ministry of Education, Tianjin 300072, China; 2 School of Civil Engineering, TianjinUniversity, Tianjin 300072, China; 3 Tianjin Metro Group Co., Ltd., Tianjin 300051, China)Abstract: The influence of foundation pit excavation on the performance of pit bottom piles should not be ignored. Based on the measured data verified finite element parameters of the project piles, parametric analysis was carried out on working performance of a single pile in different pit bottom locations under conditions of different foundation pit excavation depths and excavation plane dimensions. The finite element analysis shows that large initial tensile force may occur due to foundation pit excavation and the maximum initial tensile force of pile shaft can be 50% of the bearing capacity of the ground test pile. The maximum relative initial tensile force of pile shaft increases with the growth of the ratio of foundation pit excavation depth(B) and foundation pit excavation width(H). The maximum value of the maximum relative initial tensile force occurs when the ratio of pile length(L) and foundation pit excavation width(H) is 2～3. The relative position of maximum initial tensile force of pile shaft mainly decreases with the increase of L/H, and increases with the growth of B/H. Most of the stiffness of single piles decreases after excavation, and the minimum value can be 26.4% of the initial value. The relative stiffness may be larger than 1 when both of L/H and B/H are small. The maximum initial tensile force of pile shaft due to excavation and its position should be taken into consideration in design as well as the decrease of the single pile stiffness.Keywords: foundation pit excavation; single pile; initial tensile force of pile shaft; relative stiffness; parametric analysis*国家自然科学基金资助项目（50878144），国家重点基础研究发展计划（973计划）资助项目（2010CB732106）。作者简介：郑刚，博士，教授，博士生导师，Email:zhenggang1967@163.com。
