瞬变电磁法低阻层屏蔽问题研究
发布时间：2018-08-29 13:38
【摘要】：交通建设在国家经济发展中起着十分重要的先行作用,其中,隧道工程在铁路交通建设中所占比重逐渐增大,由于隧道周围的地质情况比较复杂,一旦地质条件发生改变,则会严重影响施工进度,甚至造成人员伤亡,所以查清隧道衬砌后的病害情况一直是隧道施工中的重要环节。目前,瞬变电磁法以高效、经济、无损等优点被广泛应用于资源勘查、水文地质调查等领域,此外,瞬变电磁法对含水构造的灵敏性也使其在隧道超前地质预报领域也取得了良好的效果。瞬变电磁法(Transient Electromagnetic Method,简称TEM)是一种基于电磁感应原理的时间域电磁探测方法。该方法利用不接地回线或者接地线源,向地下发射脉冲磁场,在其激发下,地下地质体中激励起的感应涡流将产生随时间变化的二次场,由于二次场包含与地质体有关的地质信息,所以提取二次场响应并分析其特征,能够达到探测地下介质的空间展布的目的。本文基于瞬变电磁法理论,从麦克斯韦方程组出发,推导出了水平层状大回线中心处的垂直磁场的时间域表达式。利用线性数字滤波法实现了汉克尔积分和正、余弦积分,通过对不同滤波系数的计算精度进行对比,选用140点的汉克尔J1变换滤波系数和250点的正弦变换滤波系数作为一维数值模拟的滤波系数组合。利用C语言编写的一维正演程序,计算了不同参数以及不同层状地电模型的瞬变电磁响应,对响应曲线进行对比分析,归纳总结了不同条件下响应曲线的变化特征。利用DuFort-Frankel差分方程,对两个线源和边界条件进行处理,实现了二维时域有限差分正演模拟,对均匀半空间模型、板状模型、溶洞模型和断层模型进行计算,通过对比不同延时的电场等值线图和感应电动势曲线,了解电磁波在地下的传播规律以及地质体对响应信号产生的影响,发现瞬变电磁法对低阻异常体的探测能力比高阻异常体灵敏。讨论了基于磁场强度和基于感应电动势两种全区视电阻率的定义方式,利用向外延拓和插值加密的方式可以将感应电动势转换成磁场强度,并且计算精度较高;利用二分搜索法求解反函数,分别得到两种定义方式的全区视电阻率,较好地反映了视电阻率在全时段的连续变化情况。实现了基于全区视电阻率的烟圈反演,通过对比分析多种地电模型的反演结果,发现烟圈反演对低阻异常的反映优于高阻异常,其中,利用感应电动势计算的反演结果对异常的反映优于利用磁场强度计算的反演结果,但其反演结果存在假异常,在进行资料解释的过程中需特别注意。利用一维正、反演以及二维正演,对含有低阻屏蔽层的地电模型的研究表明:低阻屏蔽层会降低瞬变电磁场的扩散速度,对感应涡流起聚集作用,削弱其下方地质体的异常反映,导致探测同样埋深的地质异常体,需要更长的观测时间。烟圈反演结果基本无法反映低阻屏蔽层下方的高阻地层,若其下伏为低阻地层,并且电阻率相对较低或层厚较大,则能从反演结果中识别。对隧道内采集的试验数据进行一系列的预处理,提高了信号的信噪比,通过烟圈反演能够快速得到深度-视电阻率剖面图,利用上述理论研究和数值模拟技术得到的解译标志,对图件进行资料解释。衬砌内的钢筋会增强感应电动势,导致反演结果的视电阻率值偏低,并且反演最大深度较小,试验结果验证了数值模拟成果的正确性,所以在存在低阻屏蔽层的工区进行瞬变电磁法勘探时,需要适当延长观测时间,并且需要加大仪器的发射功率或者采用大功率仪器,此外还需结合工区的地质资料和地球物理资料进行综合分析,提高探测的准确性。本文的研究成果不仅对隧道衬砌后病害探测具有实际意义,同样也适用于地面、水上等瞬变电磁法的勘探。
[Abstract]:Transportation construction plays a very important role in the development of national economy. The proportion of tunnel engineering in railway transportation construction is gradually increasing. Because of the complex geological conditions around the tunnel, once the geological conditions change, it will seriously affect the construction progress, even cause casualties. So after the tunnel lining is found out At present, transient electromagnetic method is widely used in resource exploration, hydrogeology survey and other fields because of its high efficiency, economy and non-destructive. In addition, the sensitivity of transient electromagnetic method to water-bearing structure also makes it achieve good results in the field of tunnel geological prediction. Transient Electromagnetic Method (TEM) is a time-domain electromagnetic detection method based on the principle of electromagnetic induction. The method uses ungrounded loop or grounded source to emit pulsed magnetic field to the underground. Under the excitation of TEM, the induced eddy current in the underground geological body will produce a time-varying secondary field due to the secondary field. Based on the theory of transient electromagnetic method and Maxwell equations, the time domain expression of the vertical magnetic field at the center of the horizontal layered large loop is derived. Hankel integral, sine and cosine integral are realized by digital filtering method. By comparing the calculation accuracy of different filtering coefficients, 140-point Hankel J1 transform filter coefficients and 250-point sine transform filter coefficients are selected as the combination of filtering coefficients for one-dimensional numerical simulation. The one-dimensional forward program written in C language is used to calculate different parameters. The response curves of different layered geoelectric models are compared and analyzed, and the characteristics of response curves under different conditions are summarized. The DuFort-Frankel difference equation is used to deal with two line sources and boundary conditions. By comparing the electric field contour map and induced electromotive force curve with different delays, the propagation law of electromagnetic wave in the ground and the influence of geological body on the response signal are understood. It is found that the detection ability of transient electromagnetic method for low resistivity anomaly body is more sensitive than that for high resistivity anomaly body. Magnetic field strength and apparent resistivity based on induction electromotive force are two definitions of the whole region, which can be converted into magnetic field strength by means of outward continuation and interpolation encryption, and the calculation precision is high; the inverse function is solved by the dichotomy search method, and the apparent resistivity of the whole region is obtained by two definitions, which better reflects the apparent resistivity. The smoke circle inversion based on the apparent resistivity of the whole region is realized. By comparing and analyzing the inversion results of various geoelectric models, it is found that smoke circle inversion is superior to high resistivity anomaly in reflecting the low resistivity anomaly, and the inversion result calculated by induction electromotive force is superior to magnetic intensity meter in reflecting the anomaly. Using one-dimensional forward, inversion and two-dimensional forward modeling, the geoelectric model with low-resistivity shielding layer is studied. The results show that the low-resistivity shielding layer can reduce the diffusion velocity of transient electromagnetic field, agglomerate the induced eddy current and weaken its underneath. The results of smoke circle inversion can hardly reflect the high resistivity formation beneath the low resistivity shielding layer. If the low resistivity formation is underlying, and the resistivity is relatively low or the thickness of the layer is large, it can be identified from the inversion results. A series of pretreatments have been carried out to improve the signal-to-noise ratio of the signal. Depth-apparent resistivity profiles can be obtained quickly by smoke circle inversion. Based on the interpretation marks obtained by the above theoretical research and numerical simulation techniques, the data of the profiles are interpreted. The reinforcing bars in the lining can enhance the induced electromotive force and lead to the apparent resistivity of the inversion results. The value is low and the maximum inversion depth is small. The experimental results verify the correctness of the numerical simulation results. Therefore, it is necessary to prolong the observation time properly, increase the transmitting power of the instruments or use high-power instruments in the transient electromagnetic prospecting in the work area with low-resistivity shielding layer. In addition, it is necessary to combine the geological resources of the work area. The research results of this paper are not only of practical significance to the disease detection after tunnel lining, but also applicable to the surface, water and other transient electromagnetic exploration.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325;U452.1
本文编号：2211366
[Abstract]:Transportation construction plays a very important role in the development of national economy. The proportion of tunnel engineering in railway transportation construction is gradually increasing. Because of the complex geological conditions around the tunnel, once the geological conditions change, it will seriously affect the construction progress, even cause casualties. So after the tunnel lining is found out At present, transient electromagnetic method is widely used in resource exploration, hydrogeology survey and other fields because of its high efficiency, economy and non-destructive. In addition, the sensitivity of transient electromagnetic method to water-bearing structure also makes it achieve good results in the field of tunnel geological prediction. Transient Electromagnetic Method (TEM) is a time-domain electromagnetic detection method based on the principle of electromagnetic induction. The method uses ungrounded loop or grounded source to emit pulsed magnetic field to the underground. Under the excitation of TEM, the induced eddy current in the underground geological body will produce a time-varying secondary field due to the secondary field. Based on the theory of transient electromagnetic method and Maxwell equations, the time domain expression of the vertical magnetic field at the center of the horizontal layered large loop is derived. Hankel integral, sine and cosine integral are realized by digital filtering method. By comparing the calculation accuracy of different filtering coefficients, 140-point Hankel J1 transform filter coefficients and 250-point sine transform filter coefficients are selected as the combination of filtering coefficients for one-dimensional numerical simulation. The one-dimensional forward program written in C language is used to calculate different parameters. The response curves of different layered geoelectric models are compared and analyzed, and the characteristics of response curves under different conditions are summarized. The DuFort-Frankel difference equation is used to deal with two line sources and boundary conditions. By comparing the electric field contour map and induced electromotive force curve with different delays, the propagation law of electromagnetic wave in the ground and the influence of geological body on the response signal are understood. It is found that the detection ability of transient electromagnetic method for low resistivity anomaly body is more sensitive than that for high resistivity anomaly body. Magnetic field strength and apparent resistivity based on induction electromotive force are two definitions of the whole region, which can be converted into magnetic field strength by means of outward continuation and interpolation encryption, and the calculation precision is high; the inverse function is solved by the dichotomy search method, and the apparent resistivity of the whole region is obtained by two definitions, which better reflects the apparent resistivity. The smoke circle inversion based on the apparent resistivity of the whole region is realized. By comparing and analyzing the inversion results of various geoelectric models, it is found that smoke circle inversion is superior to high resistivity anomaly in reflecting the low resistivity anomaly, and the inversion result calculated by induction electromotive force is superior to magnetic intensity meter in reflecting the anomaly. Using one-dimensional forward, inversion and two-dimensional forward modeling, the geoelectric model with low-resistivity shielding layer is studied. The results show that the low-resistivity shielding layer can reduce the diffusion velocity of transient electromagnetic field, agglomerate the induced eddy current and weaken its underneath. The results of smoke circle inversion can hardly reflect the high resistivity formation beneath the low resistivity shielding layer. If the low resistivity formation is underlying, and the resistivity is relatively low or the thickness of the layer is large, it can be identified from the inversion results. A series of pretreatments have been carried out to improve the signal-to-noise ratio of the signal. Depth-apparent resistivity profiles can be obtained quickly by smoke circle inversion. Based on the interpretation marks obtained by the above theoretical research and numerical simulation techniques, the data of the profiles are interpreted. The reinforcing bars in the lining can enhance the induced electromotive force and lead to the apparent resistivity of the inversion results. The value is low and the maximum inversion depth is small. The experimental results verify the correctness of the numerical simulation results. Therefore, it is necessary to prolong the observation time properly, increase the transmitting power of the instruments or use high-power instruments in the transient electromagnetic prospecting in the work area with low-resistivity shielding layer. In addition, it is necessary to combine the geological resources of the work area. The research results of this paper are not only of practical significance to the disease detection after tunnel lining, but also applicable to the surface, water and other transient electromagnetic exploration.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325;U452.1
【参考文献】
相关博士学位论文 前2条
1 杨海燕;矿用多匝小回线源瞬变电磁场数值模拟与分布规律研究[D];中国矿业大学;2009年
2 胡雄武;巷道前方含水体的瞬变电磁响应及探测技术研究[D];安徽理工大学;2014年
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