基于桩土界面的静压桩沉桩效应与承载特性室内试验研究

饱和黏性土地基中桩土界面的受力特性会对静压桩沉桩效应及长期承载力的发挥产生重要影响。通过黏性土地基中桩身表面嵌入式安装硅压阻式传感器的静压桩模型试验，分别对开口和闭口静压桩沉桩和加载过程的桩土界面超静孔隙水压力和有效径向应力进行研究。结果表明：在沉桩过程中，桩土界面超静孔隙水压力及有效径向应力随入土深度逐渐增加，沉桩结束时增量幅值随着h/D(h为传感器距桩端距离，D为桩径)增大而减小，同一h/D位置处闭口桩的增量幅值大于开口桩的；同一入土深度处，桩身不同h/D位置处桩土界面有效径向应力存在退化现象，且随着h/D和入土深度的增加退化越明显。在加载过程中，h/D=1和h/D=5位置处桩土界面超静孔隙水压力相比沉桩结束时减小，且随着h/D增大，减小幅度也增大；同一h/D位置处，桩土界面有效径向应力增量幅值随着桩顶施加荷载值增加而增大。沉桩过程和加载过程桩土界面超静孔隙水压力和有效径向应力均随着h/D的增加而减小，不同h/D位置处桩土间的有效径向应力变化是沉桩和加载过程桩土界面受力机理不同的重要原因。

Laboratory experimental study on pile jacking-in effects and capacity characteristics based on pile-soil interface

The mechanical characteristics of pile-soil interface has an important effect on pile jacking-in effects and long-term capacity for saturated clayey soil. The model tests were conducted for test piles installed by adhering with silicon piezoresistive sensors jacked into clayey soil. The excess pore pressure and effective radial stress of pile-soil interface of open-ended and closed-ended piles during pile-sinking and loading process were studied. The results indicate that the excess pore pressure and effective radial stress of pile-soil interface increase with the increase of embedded depth during pile-sinking. Increment amplitude decreases with the increase of h/D (h is the distance between the sensor and the pile end, and D is the pile diameter)when the pile-sinking ends. Increasing amplitude of closed-ended pile is larger than that of open-ended pile at the same position of h/D. The effective radial stress of pile-soil interface presents radial stress degradation with the relative depth of the pile tip(h/D) increases at the same penetration depth. The radial stress degradation presents obviously with the relative depth of the pile tip(h/D) and penetration depth increasing. Compared with time of pile-sinking ending, the excess pore pressure of pile-soil interface during loading process at the position of h/D=1 and h/D=5 decreases, the decreased magnitude increases with the increase of h/D. The increment amplitude of effective radial stress of pile-soil interface increases with the loading applied on pile top increasing at the same position of h/D. The excess pore pressure and effective radial stress of pile-soil interface during pile-sinking and loading process decrease with the increase of h/D. The variation of effective radial stress between the pile and the soil at different positions of h/D is the most important reason to introduce the difference of stress mechanism at pile-soil interface during pile-sinking and loading process.