矩形小回线源三维瞬变电磁场响应特征及堤坝渗漏探测研究

发布时间：2018-03-30 18:20

本文选题：小回线源　切入点：瞬变电磁法　出处：《中国地质大学(北京)》2015年博士论文

【摘要】：瞬变电磁法作为电法勘探的一个重要分支,因其独有的特点适用于工程地球物理探测。本文针对水库大坝和堤防渗漏探测的实际,探索用长方形小回线装置进行瞬变电磁法大坝渗漏通道探测,采用基于非均匀剖分方式的FDTD方法,来正演模拟堤坝模型中不同渗漏构造的瞬变电磁场响应特征及空间分布规律,并最终将长方形小回线源瞬变电磁法应用于大坝渗漏探测。主要研究工作与成果如下：(1)由均匀半空间解析解和层状介质数字滤波解的理论公式,推导出均匀半空间矩形回线源在时间域电磁场各分量的表达式；总结适合于复杂模型计算的非均匀复合网格有限差分计算方法,并通过对迭代步长、边界条件和激励源施加等方面的限定,实现了基于非均匀剖分的FDTD正演。在确保结果精度的基础上,提高了计算效率。(2)为了验证基于非均匀剖分三维有限差分算法的正确性,将均匀半空间模型的解析解与FDTD解进行比对,并进行误差分析,发现通电时间长短不影响早期解的精度,但通电时间越长,得到准确解的时间越长；通过对常见层状模型的数字滤波解同FDTD正演结果比对,发现该算法仅在早期时刻有一定误差,晚期时刻吻合较好,进一步检验了算法的可靠性。(3)通过对比相同等效面积的长方形与正方形回线源激励的瞬变电磁响应,提出适合堤坝瞬变电磁探测的长方形小回线装置。构建均匀堤坝模型,采用非均匀剖分方式的FDTD算法模拟均匀坝体模型的瞬变电磁场响应；在坝体中设置不同形状和类型柱状、板状、复杂渗漏异常体,通过对抽取断面的电场和磁场分量的分布来研究含渗漏异常体坝体模型的瞬变电磁场响应。结果表明,模拟结果与设置模型一致,说明该正演程序可以模拟出含多个渗漏异常体的复杂模型；并通过同均匀坝体模型响应求差的方式来研究渗漏异常体的在地表磁场分量的异常场,为下一步瞬变电磁三维反演研究提供了基础。(4)在多个水库大坝和围堰使用小回线源瞬变电磁探测方法进行了渗漏探测现场试验,探测成果为渗漏隐患的处理找准了方向,结果得到了验证。表明长方形小回线源瞬变电磁渗漏探测方法用于水利工程渗漏探测是可行的。
[Abstract]:Transient electromagnetic method, as an important branch of electrical exploration, is suitable for engineering geophysical exploration because of its unique characteristics. In this paper, the transient electromagnetic method is used to detect the leakage passage of dam with rectangular small loop device. The FDTD method based on non-uniform dissection is used to forward simulate the response characteristics and spatial distribution of transient electromagnetic field of different seepage structures in dike model. Finally, the rectangular small loop source transient electromagnetic method is applied to the detection of dam leakage. The main work and results are as follows: 1) the theoretical formula of uniform half-space analytical solution and layered medium digital filtering solution. The expressions of each component of electromagnetic field in time domain of rectangular loop source in uniform half space are derived, and the finite difference method of nonuniform composite grid for complex model calculation is summarized, and the iterative step size is given. In order to verify the correctness of the 3-D finite difference algorithm based on non-uniform dissection, the FDTD forward modeling based on non-uniform dissection is realized by the boundary condition and excitation source limitation. On the basis of ensuring the accuracy of the results, the computational efficiency is improved. The analytical solution of the uniform half-space model is compared with the FDTD solution, and the error analysis is carried out. It is found that the length of the electrification time does not affect the accuracy of the early solution, but the longer the electrification time is, the longer the exact solution is obtained. By comparing the digital filtering solutions of common layered models with the results of FDTD forward modeling, it is found that the algorithm only has some errors in the early period and the late stage is in good agreement. The reliability of the algorithm is further tested. By comparing the transient electromagnetic responses of rectangular and square loop sources with the same equivalent area, a rectangular small loop device suitable for transient electromagnetic detection of dikes is proposed, and a uniform embankment model is constructed. The transient electromagnetic field response of the uniform dam model is simulated by using the FDTD algorithm of non-uniform dissection, and different shapes and types of columnar, plate-shaped and complicated seepage abnormal bodies are arranged in the dam body. The transient electromagnetic field response of the dam body model with seepage is studied by the distribution of the electric field and magnetic field components of the extracted section. The results show that the simulation results are consistent with the set model. It shows that the forward program can simulate the complex model with multiple seepage anomalies, and study the anomalous field of magnetic field in the surface of the seepage anomaly by the method of response difference of the same uniform dam model. This paper provides the foundation for the further research of transient electromagnetic 3D inversion. (4) the leakage detection field test is carried out in several reservoirs, dams and cofferdams using the method of transient electromagnetic detection with small loop source. The results of the detection find the right direction for the treatment of potential leakage problems. The results show that the detection method of transient electromagnetic leakage with rectangular small loop source is feasible for hydraulic engineering leakage detection.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV698.1;P631.325

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