近铁路基坑通风井段变形特征及其机制分析

针对长春某地下车站深基坑工程，深入研究了基坑开挖过程中近铁路侧通风井段险情的发生过程及其致险机制。通过分析通风井附近桩身水平位移、桩顶水平位移、支撑轴力以及铁路道轨两侧路肩沉降差，探讨了通风井段基坑变形过大的原因；采用ABAQUS有限元软件对该基坑的施工过程进行数值模拟，分析了通风井段基坑施工险情的发生机制。研究结果表明，通风井段基坑变形过大是由岩土体过度应力释放和基坑变形空间效应共同作用导致。由于通风井处阳角的存在，且施工过程中通风井段基坑未架设斜撑，致使该处基坑变形的空间效应显著，坑壁产生指向通风井的扭转变形；开挖速度过快、支撑安装不及时和岩土体中过度应力释放导致围护桩变形过大，使基坑的稳定性变差。

Study on Deformation Characteristics of Ventilation Shaft Section in Foundation Pit Excavation Adjacent to Railway

In this paper, for a deep foundation pit of an underground station in Changchun, the instability crisis and its mechanism in the ventilation shaft section during the excavation of the foundation pit are studied in depth. Through the analysis of the horizontal displacement of the pile body, the horizontal displacement of the pile top, the support axial force of the bracing, and the settlement difference of the shoulders on both sides of the railway track, the major causes of the excessive deformation of the foundation pit in the ventilation shaft section are discussed. Then, the construction process of the foundation pit is simulated using ABAQUS finite element software, and the instability mechanism of the foundation pit in the ventilation shaft section is analyzed. The results demonstrate that the excessive deformation of the foundation pit in the ventilation shaft section is caused by the coupling of the excessive stress release of strata and the spatial effect of the foundation pit deformation. The spatial effect of the foundation pit deformation in the ventilation shaft section is remarkable due to the existence of positive corner in the ventilation shaft and the absence of diagonal bracing during construction, and the pit wall produces torsional deformation pointing to the inside of the ventilation shaft. The excessive excavation and unsuitable support installation lead to the excessive stress release in strata, which causes the excessive deformation of retaining piles and deteriorates the stability of the foundation pit.