Vertical bearing capacity of super-long bored piles in soft soil area
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摘要: 结合上海某软土地区的超长灌注桩试桩检测结果研究了超长灌注桩的竖向极限承载力、桩端及桩身变形特性、桩端阻力及桩侧摩阻力变化规律等性能, 首次提出： = 1 \* GB3 ① 在 超长 灌注桩施工中须采用人工造浆以保证桩基成孔质量 ； = 2 \* GB3 ② 在竖向压力作用下, 超长灌注桩桩身压缩量占总沉降量的 94% ,桩端沉降量占总沉降量的 6% , 桩身压缩量计算时桩身压缩系数取值应小于 0.5 ； = 3 \* GB3 ③ 超长灌注桩在上拔力作用下桩身变形量占总变形量的 95% ,桩端变形量仅占总变形量的 5% ,桩身上拔变形计算时桩身压缩系数可取 0.75 ～ 1.0 ； = 4 \* GB3 ④ 浅层土体侧摩阻力随荷载增加基本没有变化,深层土体侧摩阻力随荷载增加逐渐增大至稳定值； = 5 \* GB3 ⑤ 当桩端位移小于 2 mm 时,端阻力–桩端位移曲线基本呈线性变化,当桩端位移大于 2 mm 时,端阻力急剧增加。这 对于软土地区超长灌注桩的设计施工具有借鉴意义,对进一步研究桩基荷载传递机理具有重要价值。Abstract: Through the analysis of the results of super-long bored testing piles in soft soil area in Shanghai, the properties of the ultimate bearing capacity, the deformation characters of the pile tip and pile body, the change laws of side friction and tip resistance are investigated. The followings are proposed: (1) the construction of super-long bored pile should take the way of artificial drilling fluid to guarantee the quality of bored hole; (2) under the vertical pressure, the self-compression of super-long bored pile is 94% of the total settlement, and the self-compression coefficient is less than 0.5; (3) under the uplift force, the self-deformation of super-long bored pile is 95% of the total deformation, and the self-deformation coefficient is between 0.5 and 1.0; (4) the side friction of shallow layer soil keeps constant under the increasing loads, but that of deep layer soil increases to constant value; (5) the curve of tip resistance-displacement is linear varied when the tip displacement is less than 2 mm, which is rapidly changes when the tip displacement is more than 2 mm. This research is useful for the design and construction of the super-long bored piles in soft soil area. Also, it has important significance for further studies on load transfer laws of foundation piles.
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Keywords:
- super-long bored pile /
- ultimate bearing capacity /
- side friction /
- tip resistance
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