窄基坑围护墙插入深度优化解析及离心试验研究

与宽基坑相比,窄基坑由于基坑开挖宽度小,围护墙的稳定性有很大的提高。对纵向长度长达数公里的窄基坑工程,在满足稳定的前提下,如果围护墙的插入深度可以得到优化,其经济效益将是巨大的。以福建省某城区电缆隧道的窄基坑工程为依托,开展窄基坑围护墙插入深度优化的研究。首先,采用解析的方法对比了不同开挖宽度条件下围护墙的受力及变形特征。结果表明,开挖宽度减小时,作用在围护墙的水平附加荷载将大幅降低,同时墙体的内力和变形也大幅减小。基于此,提出适用于窄基坑的坑底土体抗隆起稳定性安全系数计算方法,改进规范提出的计算方法。计算结果表明,由改进的计算方法得到的安全系数大于规范方法算得的安全系数。若按照改进的计算方法进行设计,围护墙插入深度可减少25%。最后,基于离心物理模型试验对提出的理论进行验证。试验结果表明,对于窄基坑,规范提供的围护墙临界插入深度计算方法确实过于保守,在设计窄基坑时有必要对围护墙插入深度进行优化。研究成果可为窄基坑工程围护墙插入深度的优化设计提供理论依据。

Analytical solution and centrifugal test for the optimization of retaining wall insertion depth in narrow foundation pits

Compared with the wide foundation pit,the stability of the retaining wall of the narrow foundation pit is greatly improved due to its small excavation width.For narrow excavation engineering with a longitudinal length of several kilometers,optimization of the insertion depth of the retaining structure maybe bring significant economic benefits.Based on the narrow excavation of a cable tunnel in a city of Fujian province,the optimization of the insertion depth of the narrow excavation retaining structure was studied.The force and deformation characteristics of the retaining wall with different excavation widths were compared analytically.It is shown that with decreasing the excavation width,the horizontal additional load acting on the retaining wall,the internal force and deformation of the wall are greatly reduced.A new method for calculating the safety factor of anti-uplift stability of narrow excavation pits was put forward to improve the method proposed in the current specifications.The calculation results indicate that the safety factor obtained by the improved method is larger than that calculated by the current specification and that the insertion depth of the retaining wall calculated by the improved method can be reduced by 25%.For verification,centrifugal model tests were carried out.The test results show that,for narrow excavation pits,the calculation method of the critical insertion depth of the retaining structure provided by the code is indeed too conservative.Therefore,it is necessary to optimize the insertion depth of the retaining structure when designing a narrow excavation pit.The research can provide a theoretical basis for the optimal design of the retaining wall insertion depth of the narrow excavation pits.