北京地铁粉质黏土地层新型PBA车站沉降规律研究

Study on Settlement Law of New PBA Station of Beijing Metro in Silty Clay Stratum

PBA(Pile-Beam-Arch)工法已成为北京地区繁华路段地铁暗挖车站的主流工艺,但因其工序转换复杂,施工流程步序多,易引起地层沉降。新型PBA工法是在单层4导洞PBA工法的基础上,将中间导洞联合,共用中隔壁,形成CD法(中隔壁法)施工的大断面导洞,相较于传统双层8导洞PBA工法以及近些年推广的单层4导洞PBA工法,地层沉降规律难以掌握。以北京地铁22号线甘露园站为依托,运用有限元数值分析软件模拟车站施工过程,结合现场实测数据分析粉质黏土地层新型PBA车站地层沉降规律。结果表明:粉质黏土地层新型PBA车站施工过程沉降最大发生在开挖面拱顶上方;地层沉降主要发生在导洞开挖与扣拱阶段,约占整体总沉降的89.5%;受中导洞形式影响,导洞施工阶段造成的地层沉降比传统PBA车站要大。

The PBA(Pile-Beam-Arch)construction method has become the mainstream technology for underground excavation of subway stations in bustling sections of Beijing.However,due to its complex process transformation and multiple construction steps,it is prone to geological settlement.The new PBA construction method is based on the single-layer 4-guide hole PBA method,combining the middle guide hole and sharing the middle partition wall to form a large cross-section guide hole constructed by the CD(center diaphragm)method.Compared to the traditional double-layer 8-lead PBA method and the recently promoted single-layer 4-lead PBA method,it is difficult to grasp the law of geological subsidence.Based on the Ganluyuan Station of Beijing Metro Line 22,finite element numerical analysis software is used to simulate the construction process of the station.Combined with on-site measured data,the settlement law of the new PBA station in the silty clay layer is analyzed.The results show that the maximum settlement during the construction process of the new PBA station in the silty clay layer occurs above the arch of the excavation surface;Ground subsidence mainly occurs during the excavation and arching stages of the pilot tunnel,accounting for approximately 89.5%of the total subsidence.Due to the influence of the form of the pilot tunnel,the geological settlement caused by the construction phase of the pilot tunnel is greater than that of traditional PBA stations.