改扩建工程中新老护坡桩联合基坑支护技术

Foundation Pit Supporting Technology of Reconstruction and Expansion Engineering in the Older Sections of Beijing

老城区改扩建工程具有地下管线、设施等障碍物较多,场地狭窄、基坑周边建筑物距离过近的特征,基坑支护设计难度大。为解决狭小空间基坑支护难题,以北京东长安街边全国妇联办公楼改扩建工程为例,借鉴了合理利用既有结构为基坑支护服务的设计理念,提出了新护坡桩与原有建筑物钢筋混凝土外墙形成台阶式支护体系和建立新老护坡桩联合支护体系的支护设计方案,并采用MIDAS GTS NX有限元数值软件对基坑沉降进行数值仿真模拟分析。数值分析和现场监测结果表明:(1)采用上述设计方案,基坑位移值远小于设计规范值,有利于工程的安全和稳定;(2)有限元数值模拟结果与现场监测结果吻合较好,通过有限元计算成果可更加全面地分析基坑支护系统各个部位的力学响应特征。研究成果可以对类似工程项目基坑支护设计方案选择提供参考。

Deep excavation supporting design and construction in the urban areas might be frequently encountered many challenges,such as,underground utilities and structures;narrow sites;potential impact to the adjacent buildings and structures.This paper presents a case history of deep excavation design and construction in the confined spaces：All China Woman Federation office building expansion project.The excavation supporting design utilizes the existing structures to serves as the supporting structure.The existing reinforced basement wall and the new cast in place piles are combined in the design.The performance of the new piles and the existing concrete wall are numerically simulated by using MIDAS GTS NX.The numerical analysis and the construction monitoring results indicate that,⑴ the combined supporting structure had very small lateral deflections and these lateral deflections are far less than the allowable values in the design codes.⑵ the finite element analysis results were consistent with the monitored values.The numerical analysis can be used to predict the performance of the entire excavation and to predict the behavior of a concerned structure element.