层状黏性土中静压桩沉贯特性现场试验

Field test of penetration characteristics of jacked piles in layered clay

为探讨层状黏性土中静压桩的沉贯特性,依托山东东营某桩基工程开展了现场静压桩足尺试验,分析开闭口静压桩压桩力的变化规律,明确开闭口静压桩桩端阻力和桩侧摩阻力在贯入过程中的分布形式,揭示桩土界面径向土压力和孔隙水压力的分布特征以及有效径向土压力对单位桩侧摩阻力的影响机制。试验结果表明:压桩力的变化规律基本反映了土层性质的变化,土层的软硬程度制约着压桩力的变化,开口桩压桩力明显小于闭口桩压桩力,沉桩结束时开口桩占闭口桩的33.9%~79.7%;土层的软硬程度对桩端阻力的影响较大,并且闭口桩对桩端土层软硬程度的敏感性高于开口桩;桩侧摩阻力的发挥与土层的性质密切相关,受到土层变化的原因桩侧摩阻力临近深度并不明显,并且单位桩侧摩阻力出现明显的退化现象;桩土界面桩侧土压力的增长幅度与土层性质密切相关;孔隙水压力和超孔隙水压力的分布形式与土层的渗透性有关,基于水力压裂理论结合圆柱孔扩张理论推导的超孔隙水压力计算公式能较好地反映超孔隙水压力的分布特征;粉土层中有效径向土压力与单位桩侧摩阻力的比值为0.28左右,在粉质黏土层的比值为0.3,桩侧摩阻力的退化实质上是桩侧有效径向土压力的退化。

In order to investigate the penetration characteristics of jacked piles in layered clay,in-situ full-scale tests of hydrostatic piles were carried out based on a pile foundation project in Dongying,Shandong Province.The variation law of the jacking force of open and closed jacked piles is analyzed,and the distribution form of the end resistance and the shift resistance of open and closed jacked piles during jacking is discussed.The distribution characteristics of the radial soil pressure and the pore water pressure at the pile-soil interface are revealed.The influence mechanism of the effective radial earth pressure on unit shaft resistances is also revealed.The test results show that the change of the jacking force basically reflects the change of soil properties,and the soft and hard degree of soil restricts the change of the jacking force.The jacking force of open piles is obviously less than that of closed piles,and the open pile accounts for 33.9%-79.7%of the closed pile at the end of jacking.The soft and hard degree of soil layers has a great influence on the pile end resistance,and the sensitivity of closed piles to the soft and hard degree of soil layer is higher than that of open piles.The development of the shaft resistances is closely related to the properties of soil layer.The shaft resistance caused by soil layer change is not obvious near the depth,and the unit shaft resistance appears obvious degradation.The increase of the soil pressure at the pile-soil interface is closely related to soil properties.The distribution forms of the pore water pressure and the excess pore water pressure are related to the permeability of soil layer.The calculation formula of the excess pore water pressure based on hydraulic fracturing theory and cylindrical pore expansion theory can better reflect the distribution characteristics of the excess pore water pressure.The ratio of the effective radial earth pressure to the unit shaft resistance is about 0.28 in silty soil layer,and 0.3 in silty clay layer.The degradation shaft resistance actually reflects the degradation of the effective radial earth pressure.