考虑基坑开挖宽度的杆系有限元算法及试验研究

工程实践表明，狭窄基坑围护结构变形相对较小；而超宽基坑围护结构变形相对较大，并伴有明显的踢脚变形。由于目前常用的杆系有限元算法不能考虑基坑宽度对围护上土压力的影响，使狭窄基坑设计时偏于保守，造成较大浪费；较宽基坑设计时偏于危险，造成基坑施工风险。推导了可以考虑基坑宽度影响的围护结构上土压力折减因子的计算方法，对基坑工程杆系有限元分析的荷载取值进行了调整，改进了目前基坑设计采用的杆系有限元方法。针对24、32、42 m 3种宽度分别进行了离心模型试验。试验结果表明，传统的杆系有限元方法计算结果在考虑基坑宽度影响时明显与试验结果不符。应用所提理论对试验成果进行了分析，证明了方法的合理性。此方法是对目前基坑设计采用的杆系有限元方法的必要修正，值得在基坑设计时推广。

Test study and bar system FEM for foundation pits considering excavation width

Field measurements from practical projects show that the deformation of enclosure structures of narrow foundation pits is relatively smaller than that of super-wide foundation pits;and the latter is often accompanied with kick-out deformation.As the conventional finite element method commonly doesn’t consider the influence of the excavation width on earth pressure on enclosure structures,which causes the design for narrow foundation pit more conservative and results in wasting more,and it also takes more risky for design of a wide pit and creating risks during construction.This paper derives a new calculation method adopting reduction factor of load on the enclosure structure,taking impact of excavation width into consideration.From which the load value is regulated to improve the bar-system-FEM commonly used for foundation pit design.Three centrifuge model tests have been done for foundation pits with different widths of 24 m,32 m and 42 m respectively.The test results show that the calculation results of the traditional bar-system-FEM are obviously incompatible with the test results when the impact of foundation width is considered.The theory of this paper is used to analyze the test results,which proves the reasonableness of the method.This method is a necessary amendment to the bar system FEM and deserves the popularization in the design of foundation pits.