坑中坑基坑支护结构失稳模式影响分析

Analysis on Impact of Instability Modes on Pit-in-pit Foundation Pit Support Structures

摘要:

坑中坑作为工程中常见基坑形式，二次开挖引发的土体应力二次释放，会显著改变基坑整体稳定性。以南京某坑中坑基坑为工程背景，基于 Plaxis 有限元软件，采用 Hardening-Soil 土体本构模型与强度折减法，揭示坑中坑失稳破坏机制，系统分析外墙插入比与坑趾系数对基坑稳定系数的影响。研究结果表明：内坑开挖会在特定外墙插入比与坑趾系数组合下，改变基坑整体滑裂面形态，形成两类差异化隆起破坏模式；外墙插入比增大可有效提升基坑稳定系数并使其趋于稳定；坑趾系数变化直接对应不同失稳模式，是控制坑中坑安全稳定系数的关键影响参数。

Abstract:

A pit-in-pit foundation pit is a common form in engineering. The secondary release of soil stress caused by secondary excavation will significantly change the overall stability of the foundation pit. Taking a pit-in-pit foundation pit project in Nanjing as the engineering background, based on Plaxis finite element analysis, the Hardening-Soil constitutive model and strength reduction method are used to reveal the instability and failure mechanism of pit-in-pit structure, and systematically analyze the influences of the embedded ratio of the external wall and the pit toe coefficient on the stability factor of the foundation pit. The results show that under the specific combinations of the embedded ratio of the external wall and the pit toe coefficient, the excavation of the inner pit will change the whole sliding surface form of the foundation pit to form two differentiated uplift failure modes. The increase of the embedded ratio of the external wall can effectively enhance the stability factor of the foundation pit and stabilize it. The variations in the pit toe coefficient directly correspond to different instability modes, and are the key influence parameters to control the pit-in-pit safety and stability factors.