不同桩端下卧层桩基负摩阻力模型试验研究

发布时间：2018-11-24 19:39

【摘要】：研究目的:桩侧负摩阻力对桩产生下拽力,导致基桩沉降增大,竖向抗压承载安全等级降低,甚至造成桩体破坏。为分析不同桩端下卧层(黄土和粗砂)对基桩沉降和负摩阻力的影响,本文通过室内模型试验,对比研究两种下卧层情况下桩体、桩周土变形及桩身轴力分布的差异,明确基桩中性点位置的变化规律并给出建议值。研究结论:(1)下卧层对桩周土沉降的影响较小,但对桩身沉降的影响较大,相同堆载等级下粗砂下卧层的中性点位置明显低于黄土下卧层;(2)两种下卧层的桩身轴力都随堆载等级的增大而增大,但粗砂下卧层的下拉荷载和桩端反力明显大于黄土下卧层;(3)两种下卧层情况下,依据桩土相对位移和桩身峰值轴力确定的中性点位置基本一致;(4)在实际工程中应根据桩端下卧层的地质情况,采取适当措施,尽量减小基桩负摩阻力,充分发挥基桩的承载性能;(5)建议黄土下卧层中性点位置取0.51l~0.6l,粗砂下卧层可取0.6l~0.8l;(6)该研究成果可为类似工程堆载条件下桩基中性点的确定及设计提供一定的参考。
[Abstract]:The purpose of the study is that the negative friction on the side of the pile results in the downdraft force, which results in the increase of the settlement of the foundation pile, the decrease of the safety grade of the vertical compression bearing capacity, and even the destruction of the pile body. In order to analyze the influence of different pile end bedding (loess and coarse sand) on pile settlement and negative friction resistance, this paper compares the difference of pile body, soil deformation around pile and axial force distribution of pile body under two kinds of underlying layers by laboratory model test. The change rule of neutral point position of foundation pile is clarified and the suggested value is given. The conclusions are as follows: (1) the influence of the substratum on the soil settlement around the pile is small, but the influence on the settlement of the pile body is greater, and the neutral position of the substratum of coarse sand is obviously lower than that of the substratum of loess under the same grade of heaped load; (2) the axial force of pile body increases with the increase of pile load grade, but the pull-down load and pile tip reaction force of coarse sand substratum are obviously larger than that of loess substratum; (3) the position of the neutral point determined by the relative displacement of the pile and the peak axial force of the pile body is basically the same under the two kinds of horizontal layers; (4) appropriate measures should be taken to reduce the negative friction resistance of the pile in the actual engineering according to the geological conditions of the substratum of the pile end, so as to give full play to the bearing capacity of the pile; (5) it is suggested that the position of neutral point of loess substratum should be 0.51L / 0. 6l, and that of coarse sand substratum should be 0.6l0. 8l; (6) the research results can provide a certain reference for the determination and design of neutral point of pile foundation under similar engineering load condition.
【作者单位】：兰州交通大学;
【基金】：国家自然科学基金资助项目(41562014)
【分类号】：TU473.1

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