混凝土垫层对围护墙支撑效应的监测分析

控制基坑变形是保证基坑及周边环境安全的关键，而底板施工期间墙体变形的控制更是关注的重点。结合上海轨道交通某在建地铁车站基坑开挖时的变形监测数据及跟踪工况，对素混凝土垫层的支撑约束作用进行了监测分析。坑底暴露时间对底板施工阶段内的基坑变形有着显著影响，基坑暴露时间的长短是控制底板施工期间围护墙变形的关键。素混凝土垫层对围护墙体变形具有一定的支撑效应，在一定程度上能起到类似结构底板的作用。施工中应尽快完成混凝土垫层的浇筑工作，尽早发挥垫层对围护墙体的支撑作用。垫层对墙体的支撑效果与其自身的平直度等因素有很大关系，破坏垫层的整体性，则会削弱其对围护墙体的支撑作用。提出对坑底施工阶段基坑变形的控制措施，缩短底板施工阶段的暴露时间，提高垫层的整体性，加快底板施工，尽早形成底板混凝土对围护墙体的支撑作用，从而控制开挖阶段的基坑变形，对其他深基坑工程具有一定的参考价值。

Bracing Effect of Concrete Cushion to Lateral Deflection of Retaining Wall

Controlling the lateral deflection of retaining wall has become a core problem in deep excavation, and lateral deflection during bottom excavation occupies considerable proportion of that in the whole excavation works. Based on measured data and factual work of a metro station construction in shanghai, the bracing effect of concrete cushion is analyzed. As a result, the exposure time of excavation has notable influence on the retaining wall＇s lateral deflection during the period of bottom excavation. In addition, concrete cushion plays bracing function on controlling lateral deflection of the retaining wall, which is similar to the reinforcement concrete bottom plate. Accelerating the construction of concrete cushion as soon as possible can make full use of bracing effect on controlling the lateral deflection of retaining wall. Bracing effect of concrete cushion depends on several factors, such as concrete cushion＇s strength, stiff and flatness. The effect can be weakened with debasement of concrete cushion＇s entirety. Some proposals for lateral deflection controlling during bottom excavation of deep pit are offered. Shortening bottom construction time is favorable of lateral deflection controlling. Increasing concrete cushion＇s entirety and fastening construction progress of the reinforcement concrete bottom plate can reduce retaining wall＇s lateral deflection on the excavation stage. The results may be reference to other deep excavation engineering.