考虑卸荷效应钻孔灌注桩孔径时空变化规律研究

对上海地区某实际工程的钻孔灌注桩试成孔进行成孔测试，首先，统计分析测试所得孔径数据，得出了钻孔灌注桩考虑成孔卸荷效应的孔径随时间及空间的变化规律，孔径缩小量与时间呈正相关，且缩小幅度逐渐减小，最后趋于稳定；不同土层的孔径变化量不同，黏聚力c越小，内摩擦角φ越大，孔壁稳定性就越差，表现为该土层的孔径变化量越大。其次，采用科学合理的拟合公式对不同土层孔径变化进行拟合，拟合度较高，能够真实反映出孔径变化的特点和规律。最后，基于Kelvin模型，运用弹性理论，结合拟合公式，推导出更符合实际的孔径变化公式和反映孔壁稳定性的公式，并合理地解释了不同土层稳定性存在差异的原因。得出的结论对上海地区的成孔施工质量控制具有重要的价值。

Research on change law of hole diameter over time and space in drilling cast-in-place piles considering unloading effect

Hole check-up is conducted on the construction of drilling cast-in-place piles in a practical engineering of Shanghai. Firstly, the changing law of hole diameter over time and space is summarized by analyzing the data of hole diameter considering unloading effect. The diameter reduction and time have positive correlation, and the reduction range is decreased gradually over time, until the hole diameter is stable. Variable quantity of hole diameter is disparate in different soil layers. The smaller the cohesion c is and the bigger the internal friction angle φ is, the poorer the stability of hole wall will be and the larger the variable quantity of hole diameter is. Secondly, a scientific and reasonable fitting formula is applied to fit the change of hole diameter over time in different soil layers; it is shown that the formula is of high degree of fitting and can truthfully reflect the changing law of hole diameter. At last, based on the Kelvin model, a changing formula of hole diameter is deduced by utilizing elastic theories and combining the fitting formula to explain the case more exactly. And another formula which is concerned with the stability of hole wall is also deduced to explain the different stabilities of different soil layers more reasonably. Some conclusions from this paper are of great reference value in the construction of hole-forming in drilling cast-in-place piles in Shanghai area.