低應變檢測中振源及樁土相互作用的影響分析

丁瑋 柴華友 劉思浩 陳燦 聶田 胡哲

摘 要： 敲擊 回波法是基樁完整性檢測的有效方法，基于一維應力波理論，可以根據樁頂反射波質點振動速度響應曲線（包括走時、幅值及相位）來確定樁體波阻抗變化范圍及程度。然而，在實際中，樁是柱體而非桿件，截面變形不均勻。通過點源激發的波分量及在樁頂側面的反射波，分析了樁頂近場三維波動現象，并基于圓柱中縱向波對遠場波進行分析。結果表明，在測點位置及激振頻率滿足一定的要求時，三維波動特性及縱向波頻散特性可以削弱，樁的動測信號可近似用一維應力波理論來分析。在樁土相互作用下，樁體中應力波隨傳播衰減，分析了樁土剪切波速差異對應力波衰減影響規律，結果表明，應力波衰減不僅與樁土剪切波速比值有關，而且還與樁土剪切波速絕對值有關，樁體剪切波速越低、土體剪切波速越高，應力波衰減越快。

關鍵詞： 強度準則;粗粒土;強度參數;卸載;加載

中圖分類號：TU473.1? ? 文獻標志碼：A? ?文章編號：2096-6717（2020）02-0073-07

Analysis of influence of source and pile-soil interaction in low strain pile integrity testing

Ding Wei， Chai Huayou， Liu Sihao， Chen Can， Nie Tian， Hu Zhe

（School of Civil Engineering and Architecture， Wuhan Institute of Technology， Wuhan 430073， P.R.China）

Abstract：? The impact-echo method is an effective method for pile integrity testing.Based on the one dimensional （1-D） stress wave theory， the range and the extent of the changes in pile impedance can be determined from the vibration curve of reflected wave at the top of pile （including travel time， amplitude and phase）.However， in practice， a pile is a cylinder rather than a rod for the induced waves， and the section deformation is not uniform.In this study， the three-dimensional wave phenomena exhibited in the wave-field near the pile top are analyzed from the components of the wave excited by the point sources and the multiple reflections from the side of the pile top.The propagation behavior of the waves in the far-field， which is far from the top， is analyzed based on the longitudinal waves in cylinders.The results show that the three-dimensional wave in the near field and the dispersive characteristics of the waves in the far field can be mitigated， and the signals measured at the top can be approximately analyzed using 1-D stress wave theory when the receiver position and source frequency content meet some conditions.Under the interaction between the pile and the soil， the stress waves in the pile decay with propagation.The effects of shear wave velocities of pile and soil on the attenuation of stress wave are analyzed.It is shown that the stress wave attenuation is not only related to the shear wave velocity ratio of the pile and soil， but also related to the absolute values of the shear wave velocity of the pile and soil.The lower the shear wave velocity of the pile is， the higher the shear wave velocity of the soil is， and the faster the stress waves decay.

Keywords： strength criterion; coarse-grained soils; strength parameter; unloading; loading

低應變反射波法又稱錘擊 回波法，其基本原理為一維彈性桿應力波理論。通過在樁頂施加一敲擊荷載，激發的彈性波沿樁身傳播，當遇到樁身波阻抗變化截面時（如擴頸、縮頸、斷樁等），應力波會發生反射及透射現象。通過安裝在樁頂位置處的加速度傳感器可以接收到反射波質點速度響應，基于一維波動理論可以得到應力波沿樁身傳播的平均速度、缺陷類型及位置，從而對樁身完整性進行判定。……