地质雷达探测正演模拟及其工程应用

发布时间：2019-02-16 21:55

【摘要】：近年来,隧道及地下工程的发展越来越快,其面临的地形、地质条件以及探测环境越来越复杂,给地质雷达的探测及解译带来困难。针对上述问题,对地质雷达探测正演模拟开展了理论研究与物理试验,本文主要研究工作如下：(1)利用MATLAB开发了基于时域有限差分(FDTD)的二维TM波GPR探测正演计算软件。该软件从FDTD的三大要素(差分格式、解的稳定性、吸收边界条件)出发,利用二阶精度的中心差分近似把麦克斯韦旋度方程中的微分算符直接转化为差分形式,转化成地质雷达正演模拟的时域有限差分方程。同时,在数值稳定性条件和理想色散关系的基础上,计算出合理的时间采样间隔和空间离散间隔,并利用二维Yee元胞对正演模型进行网格的剖分,并且对每个网格设置对应的正演模型电性参数。但是由于受到计算机储存空间的限制,FDTD的计算模型大小是固定的、有限的,在FDTD计算中计算机无法模拟一个无限大的计算区域,因此,为了更好的模拟GPR探测发射的电磁波在无限大开域中的传播过程,加入了完全匹配层(Perfectly Matched Layer,PML)吸收边界条件。(2)利用C#开发了基于图像识别技术的GPR探测正演建模软件。该软件集成读取正演模型图像、介质参数赋值以及建模数据转换并输出的功能,可以读取利用任何画图软件画好的正演模型图像,对模型图像的不同颜色进行介质参数赋值,并转换成正演模型数据文件,供GPR探测正演计算软件运算使用,有效的简化了正演建模过程。(3)利用该GPR探测正演模拟软件的动态显示模块,通过动态输出连续时刻的场值分布图像,模拟GPR探测发射的电磁波在地下介质中的传播过程,便于更形象的了解和分析GPR探测中电磁波传播过程和规律。(4)利用该GPR探测正演模拟软件针对隧道及地下工程中的典型不良地质体(溶洞、断层)、典型结构物(钢筋、钢拱架)、典型分界面(层状、阶梯状、沟渠状)模型分别进行了正演模拟,模拟得到对应的GPR探测正演模拟结果,同时对结果进行了对比与分析。(5)针对隧道及地下工程中的典型不良地质体和典型结构物,设计了相应的GPR探测物理试验,发现GPR探测物理试验的探测验结果与数值正演模拟结果基本一致,二者互相验证,对地质雷达探测的数据解译提供了较可靠的依据。(6)总结了隧道及地下工程中典型目标体的判断准则,并在实际施工中应用,并证明判断准则是正确可靠的。
[Abstract]:In recent years, the tunnel and underground engineering are developing more and more rapidly. The topography, geological conditions and exploration environment are becoming more and more complex, which brings difficulties to the detection and interpretation of GPR. In order to solve the above problems, theoretical research and physical experiments are carried out on the forward modeling of GPR detection. The main research work in this paper is as follows: (1) the forward modeling software of two-dimensional TM wave GPR detection based on finite-difference time-domain (FDTD) is developed by using MATLAB. Based on the three elements of FDTD (difference scheme, stability of solution, absorbing boundary condition), the differential operator in Maxwell's curl equation is directly transformed into difference form by using the second-order precision central difference approximation. The finite difference time domain (FDTD) equation is transformed into the forward modeling of GPR. At the same time, on the basis of numerical stability condition and ideal dispersion relation, reasonable time sampling interval and spatial discrete interval are calculated, and the forward model is meshed by two-dimensional Yee cell. And the corresponding forward model electrical parameters are set for each grid. However, due to the limitation of computer storage space, the size of FDTD's computing model is fixed and finite, so the computer can not simulate an infinite computing area in FDTD computing. In order to better simulate the propagation of electromagnetic waves emitted by GPR in infinite open domain, a perfectly matched layer (Perfectly Matched Layer, is added. (2) A forward modeling software for GPR detection based on image recognition technology is developed by using C #. The software integrates the functions of reading forward model images, assigning medium parameters and transforming and outputting modeling data. It can read forward model images drawn by any drawing software and assign medium parameters to different colors of model images. The data file is converted into forward modeling data file, which can be used for the calculation of forward modeling software of GPR detection, which simplifies the modeling process effectively. (3) the dynamic display module of the forward modeling software using the GPR probe forward simulation software. By dynamically outputting the field value distribution image at continuous time, the propagation process of electromagnetic wave transmitted by GPR in underground medium is simulated. It is convenient to understand and analyze the electromagnetic wave propagation process and law in GPR detection more vividly. (4) the forward modeling software of GPR detection is used for typical bad geological bodies (caverns, faults) and typical structures (reinforced bar) in tunnel and underground engineering. In steel arch frame, the typical interface (layered, stepped, channel) models are simulated respectively, and the corresponding forward simulation results of GPR detection are obtained. At the same time, the results are compared and analyzed. (5) aiming at the typical bad geological bodies and typical structures in tunnel and underground engineering, the corresponding physical experiments of GPR detection are designed. It is found that the test results of GPR exploration physics experiment are basically consistent with the numerical forward simulation results, and both of them verify each other. It provides a reliable basis for the interpretation of the data detected by the GPR. (6) the judgment criteria of typical target bodies in tunnel and underground engineering are summarized and applied in practical construction, and it is proved that the criterion is correct and reliable.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU91

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