基坑开挖对坑底工程桩性能影响参数分析

Parametric analysis on influence of foundation pit excavation on the performance of pit bottom piles

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（日）的比值增大而增大；当桩长（L）与基坑开挖深度（日）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。

The influence of foundation pit excavation on the performance of pit bottom piles should not be ignored. Based onthe measured data verified finite element parameters of the project piles, parametric analysis was carried out on workingperformance of a single pile in different pit bottom locations under conditions of different foundation pit excavation depthsand excavation plane dimensions. The finite element analysis shows that large initial tensile force may occur due tofoundation pit excavation and the maximum initial tensile force of pile shaft can be 50% of the bearing capacity of theground test pile. The maximum relative initial tensile force of pile shaft increases with the growth of the ratio of foundationpit excavation depth （B） and foundation pit excavation width （H）. The maximum value of the maximum relative initialtensile force occurs when the ratio of pile length （L） and foundation pit excavation width （H） is 2 - 3. The relative positionof maximum initial tensile force of pile shaft mainly decreases with the increase of L/H, and increases with the growth ofB/H. Most of the stiffness of single piles decreases after excavation, and the minimum value can be 26.4% of the initialvalue. The relative stiffness may be larger than 1 when both of L/H and B/H are small, The maximum initial tensile forceof pile shaft due to excavation and its position should be taken into consideration in design as well as the decrease of thesingle pile stiffness.