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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2021, Vol. 55 Issue (10): 1867-1876    DOI: 10.3785/j.issn.1008-973X.2021.10.008
    
Study on defect detection of extended pile shaft under lateral low-strain integrity test
Shuang ZHAO1,2(),Jun-tao WU1,2,Xin-chen QIU1,2,Kui-hua WANG1,2,*(),Yuan TU1,2
1. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China
2. Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education, Zhejiang University, Hangzhou 310058, China
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Abstract  

The lateral velocity response of an extended pile shaft with defects of various sizes in the buried section was analyzed through model experiment, and the results were analyzed by combining with finite element analysis (FEA) results. Results show that the low-strain integrity test based on the lateral vibration characteristics of the pile can be used to distinguish the defects on extended pile shaft. The smaller the cross-sectional diameter of the defect is, the more obvious the reflection of the defect on the lateral velocity response of the pile is. As the height of the defect changes, the reflection of the top and bottom of the defect may superpose or separate, reflecting waveforms of the defect under different defect heights are inconsistent. The FEA results accorded well with the experimental results when adopting the shear flexible beam element of FEA to simulate the extended pile shaft. It is recommended that the excitation and receiving positions are both near the cap when conducting low-strain integrity test based on the lateral vibration characteristics of the pile. The depth of the defect can be inferred from the arrival time of the reflection of the defect in practical engineering.

Key words： extended pile shaft      lateral vibration      low-strain      defect detection     
Received: 06 November 2020      Published: 27 October 2021
CLC:  TU 473  
Fund:  国家自然科学基金资助项目（52178358，51779217）
Corresponding Authors: Kui-hua WANG     E-mail: gnauhszhao@163.com;zdwkh0618@zju.edu.cn
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Shuang ZHAO
Jun-tao WU
Xin-chen QIU
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Yuan TU
Cite this article:

Shuang ZHAO,Jun-tao WU,Xin-chen QIU,Kui-hua WANG,Yuan TU. Study on defect detection of extended pile shaft under lateral low-strain integrity test. Journal of ZheJiang University (Engineering Science), 2021, 55(10): 1867-1876.

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https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2021.10.008     OR     https://www.zjujournals.com/eng/Y2021/V55/I10/1867


基于水平低应变法的高承台桩缺陷检测研究

通过模型试验探究高承台桩埋藏段存在不同尺寸缺陷时的桩身质点水平速度响应，结合有限元(FEA)分析试验结果. 结果表明，基于桩的水平振动特性的低应变检测方法可以用于识别高承台桩桩身缺陷，且缺陷处截面直径越小，桩身质点水平速度响应曲线中缺陷处反射越明显. 随着缺陷高度的变化，缺陷处顶、底面反射信号可能会产生叠加或分离现象，导致不同缺陷高度下缺陷反射的波形不一致. 在数值模拟中，当采用柔性剪切梁单元模拟高承台桩时，数值模拟结果和试验结果吻合较好. 在实际工程中，当应用水平低应变法检测桩身完整性时，推荐采取近承台处激振、近承台处速度采集，可以根据缺陷处反射起振时间较精确地计算桩身缺陷埋深.


关键词： 高承台桩,  水平振动,  低应变,  缺陷检测 
Fig.1 Schematic of numerical model for analyzing lateral vibration response of extended pile shaft
部件 密度/（kg·m?3） 弹性模量/MPa 泊松比
桩 2500 40000 0.15
土 1800 30 0.35
Tab.1 Default parameters of numerical model for analyzing lateral vibration response of extended pile shaft
Fig.2 Curve of elastic impact force
Fig.3 Calculation examples of defect depth prediction based on lateral response of pile
Fig.4 Schematic diagram of path of reflected wave at defect
算例 h3 /m td /ms hpd /m |hpd ? h3| /m
算例1 0.50 3.8 0.57 0.07
算例2 5.50 7.8 5.90 0.40
算例3 0.80 5.6 0.80 0
算例4 8.00 11.6 8.50 0.50
Tab.2 Comparison of predicted depth and actual depth of defect
Fig.5 Lateral response of pile under different duration of excitation
Fig.6 Schematic of model experiment of lateral low-strain integrity test on extended pile shaft
部件 密度/（kg·m?3） 弹性模量/MPa 泊松比
桩 1 050 2 200 0.12
土 1 800 20 0.35
Tab.3 Default parameters of numerical model of lateral low-strain integrity test on extended pile shaft
Fig.7 Comparison of lateral velocity response of integrate pile between FEA results and experimental results
Fig.8 Comparison of lateral response of intact and defective piles under different excitation and receiving positions
Fig.9 Lateral response of pile under different defect diameter
Dd /cm h3 /m td /ms hpd /m |hpd ? h3| /m
5.0 0.03 — — —
4.0 0.03 2.2 0.11 0.08
3.0 0.03 2.1 0.06 0.03
2.0 0.03 2.1 0.06 0.03
1.5 0.03 2.0 0.02 0.01
Tab.4 Comparison of predicted depth and actual depth of defect
Fig.10 Lateral response of pile under different defect length
s /cm h3 /m td /ms hpd /m |hpd ? h3| /m
3 0.03 2.2 0.11 0.08
5 0.03 2.0 0.02 0.01
10 0.03 2.0 0.02 0.01
20 0.03 2.0 0.02 0.01
50 0.03 2.1 0.06 0.03
Tab.5 Comparison of predicted depth and actual depth of defect
Fig.11 Lateral response of pile under different heights of defect
Fig.12 Lateral response of pile under different buried depths of defect
h3 /m td /ms hpd /m |hpd ? h3| /m
0.03 2.0 0.02 0.01
0.46 2.9 0.45 0.01
0.80 3.6 0.79 0.01
Tab.6 Comparison of predicted depth and actual depth of defect
Fig.13 Lateral response of pile under different shear wave velocities of soil
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