基于透射波法和声波CT的桩基检测仿真研究

发布时间：2018-04-27 13:35

本文选题：桩基检测 + 声波透射法　；参考：《南昌航空大学》2017年硕士论文

【摘要】：随着我国建设工程的快速增长,大直径、超长混凝土桩基在城市建设、桥梁工程中得到广泛应用,桩基质量直接影响建筑物及桥梁的安全可靠性,因此桩基质量检测具有重要的现实意义。声波透射法主要是通过声波能量的衰减、波速和主频的变化以及波形的畸变等来判断声波传播路径上的混凝土质量,具有检测高效、结果可靠、不受桩长限制等优点,已成为桩基完整性检测的重要手段。本文通过有限元波动法模拟声波在桩身内传播,从而对获得的多种声学参数进行时域和频域分析,研究缺陷混凝土桩基中声波的传播规律。将声波层析成像技术应用于大直径桩基检测中,利用声时信息来反演桩基内部质量状况,为声波层析成像技术检测桩基缺陷提供可靠依据。主要研究内容及结论如下:(1)介绍了桩基透射波法检测技术的基本原理和信号分析方法,对声波层析成像技术在桩基检测中的理论基础、成像思路和成像反演算法进行了归纳总结,为后续的有限元模拟研究提供理论依据。(2)通过ANSYS/LS-DYNA有限元软件模拟声波在大直径桩基中传播,避免了桩基声波检测过程中传感器耦合不佳及噪音干扰的影响,通过波速的计算验证了利用有限元法计算桩身波动问题的准确性;分析了声波在缺陷混凝土中传播特性与缺陷线性尺寸变化的关系;对不同缺陷类型桩基接收信号进行了时域、频域分析,并对频谱畸变系数进行了研究,探讨竖向线性尺寸、水平方向线性尺寸、孔洞尺寸及材料参数对声波接收信号时域及频域的影响规律。研究表明:本文所选取的声波震源频谱能量集中,适用于大直径桩基信号检测分析;缺陷竖向线性尺寸、孔洞尺寸及材料参数对波速、波幅及主频幅值影响较大,缺陷水平方向线性尺寸对波速、波幅及主频幅值影响较小;频谱畸变系数能够灵敏地反映频谱能量的衰减,不同缺陷类型之间频谱畸变系数差异十分明显。(3)针对桩基检测的特殊性及复杂性,对桩基声波层析成像检测步骤进行了系统的介绍;利用有限元软件建立不同桩径的缺陷桩基模型,对声波在混凝土桩基中的传播进行模拟,以接收点首波走时为反演参数对桩身进行反演成像,对比分析声波频率分别为50kHz和100kHz的声波层析成像反演结果;建立含不同尺寸缺陷的桩基模型,模拟声波在缺陷桩基中的传播,对比分析平测和斜测两种观测系统的声波层析成像反演结果。研究表明:50kHz适合作为大直径桩基声波层析成像震源频率,100kHz适合作为1m以下直径桩基层析成像震源频率;矩形缺陷水平方向尺寸在0.4m以内时,采用平测观测系统的声波CT成像效果较好,当缺陷水平方向尺寸大于0.4m时,宜采用斜测观测系统进行声波CT成像。
[Abstract]:With the rapid growth of construction projects in China, large diameter and super-long concrete pile foundation is widely used in urban construction and bridge engineering. The quality of pile foundation directly affects the safety and reliability of buildings and bridges. Therefore, pile foundation quality detection has important practical significance. The acoustic transmission method is mainly based on the attenuation of acoustic wave energy, the variation of wave velocity and main frequency, and the distortion of wave form to judge the quality of concrete on the sound wave propagation path. It has the advantages of high efficiency, reliable results and not limited by the length of pile, etc. It has become an important means to check the integrity of pile foundation. In this paper, the finite element wave method is used to simulate the sound wave propagation in the pile body, so as to analyze the acoustic parameters in time domain and frequency domain, and to study the propagation law of acoustic wave in the pile foundation of defective concrete. The acoustic tomography technique is applied to the detection of large diameter pile foundation, and the acoustic time information is used to retrieve the internal quality of the pile foundation, which provides a reliable basis for detecting the defect of the pile foundation by the acoustic wave tomography technology. The main research contents and conclusions are as follows: (1) the basic principle and signal analysis method of pile foundation transmission wave detection technology are introduced, and the theoretical basis of acoustic wave tomography technology in pile foundation detection is discussed. The imaging idea and imaging inversion algorithm are summarized, which provides a theoretical basis for the subsequent finite element simulation research. (2) the sound wave propagation in large diameter pile foundation is simulated by ANSYS/LS-DYNA finite element software. In order to avoid the influence of poor coupling of sensors and noise interference in the detection process of acoustic wave of pile foundation, the accuracy of calculating the wave problem of pile body by finite element method is verified by the calculation of wave velocity. The relationship between the propagation characteristics of acoustic waves in the defect concrete and the change of the linear size of the defect is analyzed, and the time domain and frequency domain analysis of the received signals of the pile foundation with different defect types are carried out, and the spectrum distortion coefficient is studied, and the vertical linear size is discussed. The influence of horizontal linear dimension, hole size and material parameters on the time domain and frequency domain of acoustic wave receiving signal. The results show that the frequency spectrum of the acoustic source selected in this paper is suitable for detecting and analyzing the signal of large diameter pile foundation, and the vertical linear size of defect, the size of hole and material parameters have great influence on the wave velocity, amplitude and amplitude of main frequency. The linear dimension of the horizontal direction of the defect has little effect on the wave velocity, amplitude and main frequency amplitude, and the spectrum distortion coefficient can reflect the attenuation of the spectrum energy sensitively. According to the particularity and complexity of pile foundation detection, this paper systematically introduces the detecting steps of pile foundation acoustic wave tomography. The finite element software is used to establish the defective pile foundation model with different diameter of pile. The propagation of acoustic wave in concrete pile foundation is simulated, and the inversion imaging of the pile body is carried out using the first wave travel time of the receiving point as the inversion parameter. The inversion results of acoustic wave tomography with frequency of 50kHz and 100kHz are compared and analyzed, and the model of pile foundation with different size defects is established to simulate the propagation of acoustic wave in the defective pile foundation. The inversion results of acoustic tomography in two observation systems, flat and oblique, are compared and analyzed. The results show that: 50 kHz is suitable for large diameter pile foundation acoustic tomography focal frequency and 100 kHz for pile foundation tomography source frequency below 1m, when the horizontal dimension of rectangular defect is less than 0.4 m, When the horizontal dimension of the defect is greater than 0.4 m, the oblique observation system is suitable for acoustic CT imaging.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.16

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