坑中坑基坑内坑支护桩弯矩发展规律

坑中坑基坑是一种较为复杂且尚未得到充分研究的基坑形式。为研究基坑开挖过程中内坑支护桩的内力发展规律，进行了施工过程中的支护桩内力现场测试。通过采集桩身纵向受力钢筋的应力来反演桩身弯矩，分析了支护桩桩身弯矩在施工过程中的发展规律。通过有限元数值计算拟合了试验结果，研究了外坑开挖深度和平台宽度变化时内坑支护桩桩身弯矩的变化趋势，结果表明：坑趾系数(外坑平台宽度/开挖深度)与内坑支护桩桩身最大弯矩的变化存在着密切联系，通过拟合给出了桩身最大弯矩增长率随坑趾系数的函数曲线，桩身最大弯矩增长率可作为坑中坑基坑中内坑支护桩设计时的安全系数加以考虑。

Study on bending moment development law of supporting pile in "pit-in-pit" foundation pit

Pit-in-pit foundation pit is a more complex and not yet fully studied form of foundation pit. In order to study the internal force development law of the supporting piles of the inner pit during the excavation of the foundation pit, field tests of the internal force of the support piles during the construction process were conducted. The bending moment of the supporting pile is calculated by collecting the stresses in the longitudinal reinforcement of the pile, and the development law of the bending moment of the supported pile during the construction process was analyzed. The experimental results were fitted by finite element numerical calculation, the trend of the bending moment of the inner pit support pile was studied when the depth of the outer pit excavation and the width of the platform were varied. The results show that there is a close relationship between the pit toe factor ( the width of the platform / the excavation depth of the outer pit ) and the variation of the maximum bending moment of the inner pit support pile. The function curve of pile maximum moment growth rate of pit toe factor is given by fitting. The pile maximum moment growth rate can be considered as the safety factor in the design of pit retaining pile in pit-in-pit foundation pit.