静压敞口预应力高强混凝土管桩界面剪切性状试验研究

桩土界面剪切行为对静压敞口预应力高强混凝土(PHC)管桩沉贯性状及长期承载力特性具有至关重要的作用。通过成层土地基中桩身预埋光纤光栅(FBG)传感器的静压桩足尺试验，分别对敞口PHC管桩贯入及静载荷试验中的桩土界面剪切行为进行研究。结果表明：在贯入阶段，桩身轴力及侧摩阻力沿桩的深度方向逐渐传递，传力幅值与桩周土体性状密切相关，土层界面处轴力传递效率依次为98.2%、92.2%、96.3%、83.8%、80.5%。随着压桩循环次数的增加，同一深度土层摩阻力呈逐渐减小趋势。经历5个压桩循环后，深度6 m处的砂质粉土层摩阻力减小幅度约为46.25%，深度10m处的粉质黏土层经历3个压桩循环后摩阻力减小幅度约为12.1%；载荷试验过程中，桩侧摩阻力随着桩顶荷载施加自上而下逐步发挥。摩阻力完全发挥所需的桩土相对位移，粉质黏土层的最大，约为6.96~7.46mm，淤泥质黏土层的次之，约为6.05mm，砂质粉土层的最小，约为4.23mm；与原状土相比，重塑区土体含水量、孔隙比参数指标降低，重度、黏聚力及内摩擦角增大。桩周重塑区土体物理力学指标变化是贯入及载荷试验阶段桩土界面剪切行为不同的重要原因。

Experimental study on shear mechanism at pile-soil interface of jacked open-ended prestressed high-strength concrete pipe piles

The shear mechanism of pile-soil interface of open-ended prestressed high-strength concrete (PHC) pipe piles plays an important role during installation and static loading test. The full-scale tests were conducted on one test pile inserted with FBG sensors jacked into stratified soils. The shear mechanism of pile-soil interface of open-ended pipe piles during installation and static loading test were studied respectively. The results indicate that the axial force and shaft resistance gradually transfer along the depth during installation, and the magnitude is closely related to soil properties around pile. The transfer efficiency of axial force is 98.2 %, 92.2%, 96.3%, 83.8%, 80.5%, respectively. The shaft resistance at the same depth gradually decreases with the increase of jacking cycles. After five jacking cycles, the shaft resistances of sand silt at 6m depth decrease about 46.25% and the value of silty clay at 10m depth decreases about 12.1% after three jacking cycles. During the static loading test, the shaft resistance between pile and soil gradually mobilizes from up to down. To fully mobilize the shaft resistance, the relative displacement between pile and soil in silty clay is the maximum and about 6.96~7.46mm, the value in silt clay layer is second and about 6.05mm, the minimum value with 4.23mm appears in sandy silt. Compared with in-suit soils, the water content and void ratio of soils in remold zone decease. The parameters of unit weight, cohesion and internal friction angle increase. The variation of soil parameters in remold zone is the most important reason to cause the difference of shear mechanism at pile-soil interface during installation and static loading test.