阵列源瞬变电磁法隧道高分辨超前探测研究

发布时间：2018-08-29 18:47

【摘要】：隧道挖掘过程中经常发生一系列地质灾害现象如突水突泥等,严重威胁施工人员与设备的安全并拖延隧道施工进度,甚至打破隧址区原有地下水分布及水文生态环境,影响当地居民的正常生活。随着近些年隧道地质超前预报方法的发展,大规模地质灾害体探测技术已经逐渐趋于成熟、完善,但是由于受到复杂的地质条件、有限的施工环境等因素的限制,目前的隧道探测技术对掌子面前的储、导水构造与水力联系的精细化探测与快速解释还存在一定的问题。要实现对上述地质灾害体的精细探测,需要在新方法、新技术和新理论等方面对地球物理勘探手段提出更高要求。瞬变电磁法是一种时间域电磁探测方法,目前已被广泛应用于隧道突水突泥超前预报及地下工程水害探测中。本文借鉴雷达天线中阵列辐射的思想,提出了阵列源瞬变电磁隧道超前预报方法以期对掌子面前方不良地质进行精细化探测,进而为后续的施工与灾害治理提供科学指导。阵列源瞬变电磁在掌子面上布置多个发射单元组成阵列源、多个测点采集信号,形成“多源辐射、多点接收”的工作方式。其在方法理论和探测效果上阵列源瞬变电磁超前预报具有以下优势:首先,通过缩短发射源的供电脉宽时间,展宽辐射场源的过零点带宽,丰富辐射场中的高频谐波成分,进而提高对构造的精细分辨能力;其次,通过扩大阵列源的规模和延长发射单元长度,能够提高发射源的整体辐射能量,进而达到提高响应信号信噪比和探测深度的目的。为进一步缩短三维复杂模型正演计算时间,本文在前人的工作基础上对异构并行算法进行了二次优化,使程序计算速度在原有并行加速的基础上提高5%左右;同时,针对阵列源辐射形式对时域有限差分的辐射源加载方式进行了修改,实现了大规模阵列源瞬变电磁法时域有限差分的正演计算。采用三维时域有限差分方法对所提出的阵列源瞬变电磁隧道超前预报方法进行了三维正演模拟:模拟并对比了常规回线源和阵列源瞬变电磁响应,验证了阵列源具有更强的异常体识别能力,特别是与掌子面平行的响应分量比垂直于掌子面的响应分量具有更好的分辨能力;通过模拟分析不同参数的阵列源激发下的二次场瞬变电磁三分量响应规律,验证了扩大阵列源的规模及延长发射单元长度可以显著的增强辐射强度;通过模拟不同距离、规模尺度以及导电特性的不良地质体的瞬变电磁响应规律,发现地质灾害体的规模越大、距掌子面距离越近、电阻率越低,其阵列源瞬变电磁响应越明显;通过分析阵列源对灾害体水平方向长度变化的瞬变电磁响应规律,本文发现?Bx/?t与?By/?t响应分量分别在Y方向与X方向上具有明显的分辨优势;模拟阵列源探测掌子面前方的薄断层,分析对应的磁场分布规律,发现阵列源对薄断层有明显的响应异常,可以清晰的探测到薄断层的存在。基于正演模拟的结果,本文所提出的阵列源瞬变电磁超前探测方法有利于解决施工隧道中超前精细化探测难题,正演模拟的结果可以作为今后阵列源仪器制作的指导依据。
[Abstract]:A series of geological hazards, such as water inrush and mud inrush, often occur in the process of tunnel excavation, which seriously threaten the safety of construction personnel and equipment, delay the progress of tunnel construction, even break the original groundwater distribution and hydrological ecological environment in the tunnel area, and affect the normal life of local residents. However, due to the constraints of complex geological conditions and limited construction environment, there are still some problems in the fine detection and rapid interpretation of the reservoir in front of the face and the hydraulic connection between the diversion structure and the hydraulic connection. The fine detection of these geological hazards requires new methods, new technologies and new theories. TEM is a time domain electromagnetic detection method, which has been widely used in tunnel water and mud inrush prediction and underground engineering water hazard detection. Based on the idea of array radiation, the advanced prediction method of array source transient electromagnetic tunnel is proposed in order to fine detect the unfavorable geology in front of the face and provide scientific guidance for subsequent construction and disaster control. The method of "multi-source radiation, multi-point reception" has the following advantages: firstly, by shortening the supply pulse duration of the emitter, broadening the zero-crossing bandwidth of the emitter, enriching the high-frequency harmonic components in the radiation field, and then improving the fine resolution of the structure. Secondly, by enlarging the size of the array source and extending the length of the transmitting unit, the overall radiation energy of the emitter can be increased, and the signal-to-noise ratio of the response signal and the detection depth can be improved. In order to further shorten the forward computing time of the three-dimensional complex model, the heterogeneous parallel algorithm is carried out on the basis of previous work. Secondary optimization improves the computing speed of the program by about 5% on the basis of the original parallel acceleration. At the same time, the finite-difference time-domain (FDTD) loading method is modified for the array source radiation form, and the finite-difference time-domain (FDTD) forward calculation of large-scale array source transient electromagnetic method is realized. The three-dimensional forward modeling of the array source transient electromagnetic tunnel prediction method is carried out. The transient electromagnetic response of the conventional loop source and the array source is simulated and compared. It is verified that the array source has a stronger ability of anomaly recognition, especially the response component parallel to the face has a better resolution than the response component perpendicular to the face. By simulating and analyzing the three-component transient electromagnetic response of the secondary field excited by the array source with different parameters, it is verified that the radiation intensity can be significantly enhanced by enlarging the size of the array source and extending the length of the transmitting unit. It is found that the larger the scale of geological hazard body, the closer to the face, the lower the resistivity, the more obvious the transient electromagnetic response of array source. Analog array source detects thin faults in front of the face and analyzes the corresponding magnetic field distribution law. It is found that the array source has obvious abnormal response to thin faults and can clearly detect the existence of thin faults. The results of forward modeling can be used as guidance for the future production of array source instruments.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U452.11;P631.325

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