盖挖逆作法地铁车站中间桩基础选型研究

Study on Selection of the Intermediate Pile Foundation of Subway Stations with Cut and Cover Top-down Method

对于盖挖逆作法地铁车站,其施工期间的竖向支撑系统由周边的基坑支护结构和中间立柱及柱下桩基础共同组成,竖向支撑系统的稳定性是工程成败的关键。中间桩基础承载着顶板覆土、顶板及中楼板结构自重、道路车辆荷载及施工荷载等,应结合工程地质情况、柱网布局、中间立柱型式、施工要求等条件进行中间桩基础的选型、承载力和沉降计算。文章以武汉地铁中南路站为例,对盖挖逆作法车站竖向支撑系统的柱下桩基础的四种方案进行了比选研究,通过分析中间桩基础的承载力、沉降、工期和经济性要求,最终确定采用全液压可控旋挖扩底灌注桩方案施工。现场试桩、施工反馈以及变形监测结果表明:采用全液压可控旋挖扩底灌注桩工艺,各桩桩顶沉降不超过3.7 mm,施工期间地面沉降为6.45 mm,能够很好地满足桩身及周围建筑沉降控制要求;同时,全液压可控旋挖扩底灌注桩方案,造价相对较低,施工工期最短,是武汉地铁中南路站的最佳选型方案。

For the subway station constructed with cut and cover top-down method,the vertical supporting system used during the construction is composed of the foundation pit supporting structure,intermediate column and pile foundation under the column,and the stability of the vertical supporting system is the key to the success of the proj⁃ect.Since the intermediate pile foundation bears the roof casingsoil,the dead weight of the roof and the intermediate floor structure,the road vehicle load and the construction load,etc.,the selection,bearing capacity and settlement calculations of the intermediate pile foundation should be carried out according to the engineering geological condi⁃tions,the layout of the column network,the type of intermediate column and the construction requirements.Taking Zhongnan Road Station of Wuhan Metro as an example,comparison among four schemes of the pile foundation un⁃der column for the vertical support system of the station with cut and cover top-down method is conducted in this pa⁃per.By analyzing the bearing capacity,settlement,construction period and economic requirements of the intermedi⁃ate pile foundation,it is finally decided to use the scheme of screw-drilled under-reamed hydraulically cast-in-situ pile for construction.The pile test on the site,construction feedback,and deformation monitoring results show that the settlement of each pile top is no more than 3.7 mm and the ground settlement is 6.45 mm during construction af⁃ter the technology of screw-drilled under-reamed hydraulically cast-in-situ pile is used,which can meet the settle⁃ment control requirements for pile body and surrounding buildings very well.Besides,with a lower cost and shortest construction period,the scheme of screw-drilled under-reamed hydraulically cast-in-situ pile is the best one for Zhongnan Road Station of Wuhan Metro.