瞬變電磁法低阻層屏蔽問題研究
發(fā)布時間：2018-08-29 13:38
【摘要】：交通建設在國家經(jīng)濟發(fā)展中起著十分重要的先行作用,其中,隧道工程在鐵路交通建設中所占比重逐漸增大,由于隧道周圍的地質(zhì)情況比較復雜,一旦地質(zhì)條件發(fā)生改變,則會嚴重影響施工進度,甚至造成人員傷亡,所以查清隧道襯砌后的病害情況一直是隧道施工中的重要環(huán)節(jié)。目前,瞬變電磁法以高效、經(jīng)濟、無損等優(yōu)點被廣泛應用于資源勘查、水文地質(zhì)調(diào)查等領域,此外,瞬變電磁法對含水構(gòu)造的靈敏性也使其在隧道超前地質(zhì)預報領域也取得了良好的效果。瞬變電磁法(Transient Electromagnetic Method,簡稱TEM)是一種基于電磁感應原理的時間域電磁探測方法。該方法利用不接地回線或者接地線源,向地下發(fā)射脈沖磁場,在其激發(fā)下,地下地質(zhì)體中激勵起的感應渦流將產(chǎn)生隨時間變化的二次場,由于二次場包含與地質(zhì)體有關(guān)的地質(zhì)信息,所以提取二次場響應并分析其特征,能夠達到探測地下介質(zhì)的空間展布的目的。本文基于瞬變電磁法理論,從麥克斯韋方程組出發(fā),推導出了水平層狀大回線中心處的垂直磁場的時間域表達式。利用線性數(shù)字濾波法實現(xiàn)了漢克爾積分和正、余弦積分,通過對不同濾波系數(shù)的計算精度進行對比,選用140點的漢克爾J1變換濾波系數(shù)和250點的正弦變換濾波系數(shù)作為一維數(shù)值模擬的濾波系數(shù)組合。利用C語言編寫的一維正演程序,計算了不同參數(shù)以及不同層狀地電模型的瞬變電磁響應,對響應曲線進行對比分析,歸納總結(jié)了不同條件下響應曲線的變化特征。利用DuFort-Frankel差分方程,對兩個線源和邊界條件進行處理,實現(xiàn)了二維時域有限差分正演模擬,對均勻半空間模型、板狀模型、溶洞模型和斷層模型進行計算,通過對比不同延時的電場等值線圖和感應電動勢曲線,了解電磁波在地下的傳播規(guī)律以及地質(zhì)體對響應信號產(chǎn)生的影響,發(fā)現(xiàn)瞬變電磁法對低阻異常體的探測能力比高阻異常體靈敏。討論了基于磁場強度和基于感應電動勢兩種全區(qū)視電阻率的定義方式,利用向外延拓和插值加密的方式可以將感應電動勢轉(zhuǎn)換成磁場強度,并且計算精度較高;利用二分搜索法求解反函數(shù),分別得到兩種定義方式的全區(qū)視電阻率,較好地反映了視電阻率在全時段的連續(xù)變化情況。實現(xiàn)了基于全區(qū)視電阻率的煙圈反演,通過對比分析多種地電模型的反演結(jié)果,發(fā)現(xiàn)煙圈反演對低阻異常的反映優(yōu)于高阻異常,其中,利用感應電動勢計算的反演結(jié)果對異常的反映優(yōu)于利用磁場強度計算的反演結(jié)果,但其反演結(jié)果存在假異常,在進行資料解釋的過程中需特別注意。利用一維正、反演以及二維正演,對含有低阻屏蔽層的地電模型的研究表明:低阻屏蔽層會降低瞬變電磁場的擴散速度,對感應渦流起聚集作用,削弱其下方地質(zhì)體的異常反映,導致探測同樣埋深的地質(zhì)異常體,需要更長的觀測時間。煙圈反演結(jié)果基本無法反映低阻屏蔽層下方的高阻地層,若其下伏為低阻地層,并且電阻率相對較低或?qū)雍褫^大,則能從反演結(jié)果中識別。對隧道內(nèi)采集的試驗數(shù)據(jù)進行一系列的預處理,提高了信號的信噪比,通過煙圈反演能夠快速得到深度-視電阻率剖面圖,利用上述理論研究和數(shù)值模擬技術(shù)得到的解譯標志,對圖件進行資料解釋。襯砌內(nèi)的鋼筋會增強感應電動勢,導致反演結(jié)果的視電阻率值偏低,并且反演最大深度較小,試驗結(jié)果驗證了數(shù)值模擬成果的正確性,所以在存在低阻屏蔽層的工區(qū)進行瞬變電磁法勘探時,需要適當延長觀測時間,并且需要加大儀器的發(fā)射功率或者采用大功率儀器,此外還需結(jié)合工區(qū)的地質(zhì)資料和地球物理資料進行綜合分析,提高探測的準確性。本文的研究成果不僅對隧道襯砌后病害探測具有實際意義,同樣也適用于地面、水上等瞬變電磁法的勘探。
[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.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P631.325;U452.1
本文編號：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.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P631.325;U452.1
【參考文獻】
相關(guān)博士學位論文 前2條
1 楊海燕;礦用多匝小回線源瞬變電磁場數(shù)值模擬與分布規(guī)律研究[D];中國礦業(yè)大學;2009年
2 胡雄武;巷道前方含水體的瞬變電磁響應及探測技術(shù)研究[D];安徽理工大學;2014年
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