基于桩身应力测试的静压PHC管桩贯入机制

压桩过程中PHC管桩侧摩阻力与端阻力的分离是制约其贯入机制及承载力研究的瓶颈。通过桩身预埋准分布式FBG光纤传感器，对贯入成层土地基中5根足尺开口PHC管桩侧摩阻力及端阻力发展变化情况进行了监测。试验表明，准分布式光纤传感测试技术现场可操作性强，粗放施工环境下贯入阻力分离效果较为理想。成层土地基中压桩力曲线基本反映地层土性变化，桩端土层性状对压桩力影响较大。硬质土层界面处试桩压桩力平均增幅约为64.06%，端阻力受地层变化影响更为显著，平均增长幅度约为97.41%，侧摩阻力平均增长幅度约为17.92%；桩端位于非硬质土层试桩压桩力变化不明显。贯入过程中现场足尺试验桩身应力变化不同于室内模型试验，桩身上、下部侧摩阻力发挥的力学机制不同。受现场粗放施工条件及深度方向土层变化影响，贯入成层土地基中桩侧摩阻力临界深度现象不明显。

Penetration mechanism of jacked PHC pipe piles based on pile stress measurement

The separation of side resistance and toe resistance of PHC pipe piles during installation restricts the study of its penetration mechanism and bearing capacity. Full-scale tests are conducted on 5 opened PHC pipe piles jacked into stratified soils to monitor the variation of side resistance and toe resistance during installation base on quasi-distributed Fiber Bragg grating sensors. The results indicate that quasi-distributed optical fiber technology has strong operability and installation resistance separation is obtained well under bad construction condition. The variation of pile jacking force in stratified soils basically reflects the soil parameters difference, and the soil under pile toe has more influence on jacking force. The test piles jacking force, which pile toe locates on bearing layer, increases about 64.06% when jacks into the bearing layer, while the increment of toe resistance and side resistance are 97.41% and 17.92%, respectively; The pile jacking force variation is not significant which toe doesn’t locate on bearing layer. The variation of pile stress in field test is different from indoor experiments during installation, in which the mechanism of side resistance in upper is different with bottom; and the critical depth phenomenon of side resistance is not obvious because of bad construction condition and soil variation in depth.