| 摘要: | 摘 要 本研究目的在探討如何應用時間域電磁法探測地下金屬，從尋求判別地下金屬的暫態電壓表徵、製作儀器以提高訊號/雜訊比與使用最佳的探測模式以提高施測效率等三方面著手，除探測地下金屬導體存在與否，並可測定其位置。 由於金屬的導電率約 107S/m 較背景地層導電率（約 100-10-3S/m）大，金屬的渦電流衰減較緩慢，因此在接收線圈上，晚期由金屬感應產生的暫態電壓值相對於由背景地層所感應產生者為大，這種暫態電壓晚期比背景值大且緩慢衰減的現象，可以作為判別地下金屬是否存在的暫態電壓表徵。以暫態電磁儀輸出的電流訊號控制的觸發式電流放大器可以增加一次磁場的強度，除可以增加探測深度外，最重要的是工程環境下可以增加訊號/雜訊比，提升探測的效果。電流方向切換器可藉切換發射線圈的電流方向檢核暫態電壓資料的正確性。除尋求地下金屬的暫態電壓表徵與製作儀器之外，本研究也規劃出可以適用於不同環境條件與工程需求的地下金屬探測模式與線圈配置，並整合成粗略探測及精確探測二種適用的模式。 粗略探測模式在屏東測區，探測出地下鋼板的位置與形狀，經開挖後已證實探測結果正確，並且可以測出鋼板樁的深度。精確探測模式在南投測區，測定出地下全套管基樁的位置與長度，經比對後也確定與原始設計圖相符，另外以線圈圍在橋柱上進行小線圈井測，可以量出連結於橋柱的地下基樁深度。 ABSTRACT The purpose of this research is to apply time-domain electromagnetic method (TEM) to detect the underground metals. We concentrated on the three topics: to recognize the characteristics of the transient voltage by metal, to create a powerful transmitter for enhancing the signal to noise ratio, and to design better detection modes for the efficiency of field work. With those tools in use, it is not only easily judging the existence of metal conductors but also detect their locations. The fact that the electric conductivity of metal (about 107S/m) is much larger than that of the background stratum (100-10-3S/m), together with the slower decay of eddy electric current of metal, the transient voltage of the metal is more anomalous than that of the background stratum. This phenomenon is the key point used to judge if the metals exist or not. We created a powerful transmitter; it synchronized with the TEM consol and transmitting current as high as 40 A. Moreover, many transmitters can be used in parallel to produce as much current as needed. For example, three sets of transmitter parallel connected will produce current 120 A in the transmitter loop. Other than enhance the signal to noise ratio, it can increase the depth of detection. Thus, promotes the detection effects, especially under the noisy engineering environments. After the many case studies in various environmental conditions and engineering requirements, we also designed better detection modes for the efficiency in the fieldwork, that is the rough detection mode and the detail detection mode. One thing worth mentioning, experience tell us that by changing the transmitter current and checking the anomaly inverse is a worthy tip to reconfirm the signal. Finally, two successful cases are shown. Case 1, in Pingtong survey area, the rough detection mode was used to explore the position and shape of the underground steel plate, the depth of the steel stake was analyzed and the validity of the exploration was proved. Case 2, in Nantou survey area, the detailed detection mode to determine the position and length of the underground sleeve stakes was undertaken; correlated with the original design was obtained. Furthermore, by surrounding the coils around the bridge pillars and doing TEM survey, the depth of the underground stakes connected with the bridge pillars could be obtained. |
