针对既有工程桩性状测试难题,现有研究提出了一种对其桩底和完整性检测的旁孔法。当桩顶非裸露无竖向激振工作面而水平激振时,现有利用桩身透射的首至P波进行桩底和完整性检测的方法,在饱和地基下往往难以有效。为此,本文提出了一种通过水平激振激发桩身弯曲波,在合理激振﹣旁孔布置下可有效接收桩身透射首至S波(F-S波),再将其用于饱和地基下既有工程桩性状测试和评估。通过有限元手段验证了饱和地基下旁孔透射首至P波测试分析存在的局限性,以及旁孔透射首至S波用于评估桩底深度和桩身完整性的效果。结果表明:(1)饱和地基下垂直激振方向布置旁孔,接收到的信号易于识别首至F-S波,通过读取首至波走时确定两拟合直线及其交点,并由文中推荐算式对交点校正,以此确定桩底深度的方法简易、精度高;(2)当桩身存在离析类缺陷时,旁孔透射首至F-S波在缺陷附近呈现为上下平行、中间为连接过渡段的三折线,此时缺陷起始位置可由三折线的连接过渡段起始点确定。基于旁孔剪切波的方法,为饱和地基下评估既有工程桩底深度及桩身完整性提供了一种有效检测手段。
For solving the difficulties in the bottom depth and integrity evaluation of existing piles, a parallel seismic (PS) test in existing research is proposed. The existing PS testing of using the first arrival of P wave transmitted from the pile shaft to evaluate the bottom depth and integrity is invalid in saturated soil, as it is difficult to excite the pile shaft with inaccessible pile tops in vertical direction. This paper is to provide a PS testing approach using the shear wave induced by horizontal impact on the lateral surface of a pile. Under appropriate excitation-testing hole arrangement in PS testing, the first arrival of shear wave (F-S wave) received at a certain depth of testing hole transmitted from the pile shaft, can be used to evaluate the bottom depth and integrity of existing piles in saturated soil. Finite element method is used to verify PS testing limitations of the first arrivals of P wave and the effectiveness of the first arrivals of shear wave in evaluating pile bottom and integrity for existing piles by horizontal impact on the lateral surface of a pile in saturated soil. The results show that: (1) When the testing holes are arranged perpendicular to the excitation direction in saturated soil, the first arrival of F-S wave in the received signal can be identified easily. By reading the first F-S wave travel time, the two fitting lines and their intersection points are determined and the intersection points are corrected by the recommended method, so as to determine the pile bottom depth more easily with higher precision. When there is a segregation defect in the pile body, the first F-S wave arrivals present a broken line consisting of two parallel lines and a connecting line in between. It is recommended that the depth of the top of the defect can be estimated based on the beginning point of the connecting line. The proposed PS testing method provides an effective means for evaluating the depth of pile bottom and the integrity of pile body in saturated foundation.
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