坑中坑型式非对称基坑围护体系力学特性研究

Research on the Mechanical Characteristics of Asymmetrical Foundation Pit-in-pit Bracing System

研究目的:坑中坑是工程中应用较为普遍的一种非对称基坑型式,目前相关的理论研究较少,工程设计中往往凭经验确定其影响范围。本文结合南京青奥轴线地下工程上部悬臂、下部设置内支撑的基坑工程,通过有限元计算分析,探讨坑中坑型式非对称基坑围护结构的变形和土压力分布特征,旨在为工程设计提供参考。研究结论:(1)内、外坑围护距离以及内坑开挖深度对坑中坑围护结构变形和受力影响显著;(2)随着内、外坑围护距离的不断缩小,内坑围护向坑外的变形不断减小直至偏向坑内,内坑围护外侧土压力可按外坑为地表计算且考虑一定的安全系数;(3)随着内坑开挖深度加大,内坑围护偏向基坑外侧位移加大;内坑未开挖或开挖较浅时,坑底以上外坑围护结构侧向土压力介于主动土压力和静止土压力之间;内坑开挖较深时,坑底以上土压力接近主动土压力,直至坑底逐步接近静止土压力;(4)本研究结果对类似基坑工程的分析与计算具有参考价值。

Research purposes： Pit - in - pit is a kind of widely used asymmetric foundation pit, but the corresponding theory is not mature and correlative research reports are few, so that the extent of the impact is always determined by experiences. Based on the underground engineering in Nanjing Youth Olympic Axis Project, with characteristics of upper cantilever and lower internal bracing, through the finite element analysis, the deformation of retaining structure of this pit -in -pit asymmetry foundation and soil pressure distribution was studied, and the results can provide a reference for engineering design. Research conclusions： （ 1 ） The distance between inner and outer pit retaining, as well as the excavation depth of the inner pit affect the deformation and stress in pit retaining structure significantly. （2） As the distance between inner and outer pit retaining shrinks, the deformation of the inner pit, with a direction to the outer retaining, decreases continuously until bias to the inner pit, then the lateral earth pressure of the inner retaining structure can be calculated as the case of normal earth surface, while considering certain safety factor. （3） When the pit excavation depth increases, the lateral displacement to the outside of the inner pit also increases ; when the inner pit has not been dug or the excavation is very shallow, the earth pressure on the pit retaining structure above the bottom is between the active earth pressure and the earth pressure at rest; when the pit excavation is deep, the earth pressure above the bottom is close to active earth pressure, and to the bottom gradually approaching to the earth pressure at rest. （4） The research results provide valuable reference for analysis and calculation of similar projects.