地铁车站洞桩法施工对地层及邻近桩基的影响规律

Analysis of Stratum Deformation and Pile Foundation Response During Subway Station Built by Pile-Beam-Arch Construction Method

以北京地铁国贸站工程为背景，分析大跨度分离式地铁车站采用洞桩法施工，对周围地层及邻近桩基的影响．采用现场实测方法分析洞桩法施工地层沉降的规律，认为纵向沉降明显分为前期沉降区、急剧沉降区和沉降收敛区，而急剧沉降区又分为导洞、扣拱及下部开挖3个阶段；横向沉降符合Peek曲线，影响范围为3～4倍洞径．采用三维数值分析方法模拟施工过程，选取典型的邻近桩基所在断面，研究车站施工对邻近桩基变形以及地表沉降的影响，对国贸站邻近桩基变形现场量测数据进行对比分析，认为邻近桩基沉降变形与其施工过程相对应，也分为导洞、扣拱及下部土体开挖3个阶段．影响沉降盼主要因素是其空间位置，特别是桩基与车站结构的最小距离，其次桩端所处的地层条件也有一定的影响；施工对邻近桩基水平方向的扰动影响非常显著，扣拱施工对邻近桩基的侧向变形影响最大．在此基础上总结了车站上侧桩、中侧桩、下侧桩等邻近桩基的变形规律．

Based on the construction of Beijing subway line 10 of Guomao station, the influence law of surrounding stratum and adjacent pile foundation is analyzed as the large span separation-formula subway station is built by Pile-Beam-Arch construction method. The field measurement indicates that： （1） the longitudinal stratum settlement caused by the hole-pile construction can be discribed in three areas, named as： initial settlement, sudden settlement, and convergent area of the settlement. And the sudden depressed section can be defined in three stages： the lead-hole＇s construction, the buckle arch, the lower part＇s excavation; （2） The horizontal deformation conforms to the Peck curve and the af- fected area is 3-4 times of hole-diameter. Using three dimensions dynamic numerical simulation during construction process, the distortion of neighboring pile foundation as well as the surface settlement caused by station construction are analyzed. The result matches well with field monitoring data. It shows that the neighboring pile foundation＇s settlement and the deformation are consist of three steps：lead-hole＇s excavation, the buckle arch, the lower part＇s soil excavation, which is corresponded to the construction process. Some useful conclusion is drawn in this paper. Firstly, it is indicated that the key factor of settlement influence of construction to adjacent pile foundation is space posit.ion between the pile and station, such as the minimum distance between the pile foundation and the station structure etc.. Secondly, it is obtained that the stratum condition which near the pile end also contributes certain influences on this settlement; Further more, it is introduced that the disturbing influence of construction to adjacent pile foundation in the horizontal direction is extremely remarkable, the buckle arch construction has the biggest influence to the lateral deformation of neighboring pile foundation. At last, the deformation of the side pile, middle side pile, low side pile and the other neighboring pile foundations are summarized in the article.