复杂异形深基坑双环形内支撑体系 设计及受力变形特性

北京地铁 R4 线北京朝阳站地下 3 层和地下 4 层基坑具有平面几何形状复杂、各级基坑开挖深度不同以及 基坑周边附加荷载不对称等特点。为解决常规基坑支护方案不适应本基坑的问题，研发了直径不相等的双环形钢 筋混凝土内支撑体系并成功实施。详细介绍了双环形内支撑体系的布置、结构参数及施工步序，采用数值模拟方 法建立模拟基坑开挖支护的三维数值计算模型，并结合支护结构变形和受力的实测结果，探讨双环形内支撑体系 的受力和变形特性。结果表明：其围护结构变形、钢筋混凝土支撑和钢筋混凝土环梁的轴力、钢筋混凝土环梁收 敛等指标均满足控制值要求。工程实践表明：钢筋混凝土双环形内支撑体系具有布置方式灵活、对空间形状不规 则基坑具有较好的适应性、基坑内部作业空间开阔等优势。

Design and Mechanical Characteristics of Double-ring Supporting System for Complex and Irregular Deep Foundation Pits

Foundation pits on the third and fourth floors of Beijing Chaoyang Railway Station on Beijing Metro Line R4 exhibit complex plane shapes, different excavation depths at all levels, and asymmetric additional loads around the foundation pits. To address the issue of conventional foundation pit support schemes, which are unsuitable for foundation pits, a double-ring reinforced concrete internal support system with unequal diameters is developed and successfully implemented. This paper discusses the layout, structural parameters, and construction steps of a double-ring support system in detail. A three-dimensional numerical calculation model is established to simulate the process of foundation pit excavation and supporting system construction. Combined with the measured results of deformation and stress of the double-ring support system, the stress and deformation characteristics of the double-ring support system are discussed. The results show that the indicators of the double-ring support system, such as the deformation of the retaining wall, axial force of the concrete support and concrete ring beam, and convergence of the concrete ring beam, satisfy the requirements of the control value. Engineering practice reveals that the reinforced concrete double-ring support system exhibits a flexible layout, adapts well to irregular spatial shapes of foundation pits, and provides ample working space within the foundation pit.