人工挖孔桩低应变反射波法完整性检测的局限性研究

目前国内外对低应变完整性检测的局限性所做的研究主要集中于尺寸效应,而对于在自身成桩工艺及周边地层的综合影响下的人工挖孔桩低应变反射波法完整性检测的局限性少有涉及。介绍了低应变反射波完整性检测原理,结合湖南某电厂工地进行了大量的现场检测,采集测试曲线进行分析,利用钻芯法对若干检测时程曲线异常的基桩进行验证,作出正确判断,并在人工挖孔桩低应变反射波法完整性检测的局限性这个问题上进行了深入研究。最终得出相应结论桩周地层、桩端持力层的性质及桩长会影响桩端反射,护壁、桩周地层变化、阻抗变化界面处的二次反射都将对低应变检测产生干扰,桩土相互作用下可能会使低应变检测失效。

Research on the Limitations of Wave Reflection Method in Low Strain Integrity Testing for Hand-dug Pile

Previous researches on the limitations of low strain integrity testing with wave reflection method were focused on the size effect of stress wave propagation. The limitations of integrity testing for hand-dug pile in consideration of the pile-forming process and the pile’s surrounding strata were rarely researched. With the construction site of a powerplant in Hunan province as an example, we carried out a large number of field low-strain tests on hand-dug piles, and analyzed the collected time-history curves. Through core-drilling method, we checked the foundation piles with abnormal time-history curves, and estimated their integrity. We conclude that the pile tip reflection is affected by surrounding strata, properties of the bearing layer of pile tip, and pile length. The low strain testing with wave reflection method is interfered by hole-protection wall, variation of pile surrounding strata, and secondary reflection at the interface with different impedances. It will probably fail to detect under the influence of interaction between pile and soil.