框筒结构体系下变桩长CFG桩复合地基基底反力及变形特性试验研究

Experimental study of base reaction and deformation characteristic of variable-length CFG pile composite foundation for frame-tube structure

通过框筒结构体系下变桩长CFG桩复合地基模型试验,实测得到了其基底反力及变形特征并进行了分析,得出了以下结论:(1)采用长桩强化核心筒区、短桩相对弱化外框架柱区,核心筒与外框柱中间区域采用中等长度桩,在使用荷载水平下,基础中轴线纵向挠曲为0.25‰,基础对角线纵向挠曲为0.21‰。(2)在使用荷载水平下,核心筒区桩顶应力明显高于外框架柱区,核心筒区桩顶应力相对均匀,角桩最大,边中桩次之,中心桩最小;核心筒区桩间土应力与外框架柱区相差不大,整体上桩间土应力分布较为均匀,3个分区的桩间土承载力均可充分发挥。(3)在使用荷载水平下,核心筒区基底反力最高,分布较为均匀,呈线性分布;核心筒区至外框柱区基底反力逐步衰减;外框柱区域基底反力最低,分布较为均匀,基本呈线性分布;基底反力总体上呈盆形分布,基底反力分布与复合模量相关性明显,大致成线性关系。

The base reaction and deformation features are analyzed based on measured data, according to model test of variable-length CFG pile composite foundation for frame-tube structure. Some conclusions are drawn as follows. First, under the working loads, longitudinal deflection of medial axis of foundation is 0.25‰, and longitudinal deflection of diagonal direction of foundation is 0.21‰, as adopting long piles to strengthen the area of core-tube, short piles to weaken the area of outside frame column, and middle length piles between area of core-tube and area of outside frame column to transit. Second, under the working loads, the pile top stress of core-tube is obviously higher than pile top stress of outside frame column. Pile top stress of core-tube area is relatively uniformly. The biggest pile top stress is on the corner pile, next is on the side pile, and the smallest is on the center pile in the area of core-tube. Soil stress between area of core-tube and area of outside frame column is little difference. The distribution of soil stress is even distribution both in area of core-tube and outside frame column, and bearing capacity of soil among piles of three areas all can play fully. Third, under the working loads, the highest stress of the base force is in area of the core-tube, distributes relatively uniformly and shows linear distribution basically. Base reaction is gradually weak from area of core-tube to area of outside frame column. The lowest stress of the base force is in area of outside frame column, its distribution is relatively uniformly and basically line-shaped. The base reaction basically shows basin-shaped. Distribution of base reaction is obviously related with composite modulus, which is basically linear relationship.