A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels
A new method of 3D direct current resistivity modelling using a long electrode source for forward probing in tunnels
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一种使用长电极源进行隧道正向探测的 3D 直流电阻率建模新方法
DOI：
10.1002/nsg.12224
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发表时间：
2022
影响因子：
1.6
通讯作者：
Xiaoping Wu
中科院分区：
文献类型：
--
作者：
Daiming Hu;Bülent Tezkan;Mingxin Yue;Xiaodong Yang;Xiaoping Wu
直流电阻率法已广泛应用于地铁隧道、矿井巷道含水结构的预测。传统的直流电阻率采用隧道中的点电极源来激发电场；隧道掌子面背面布置电位电极，利用视电阻率测深曲线测量异常位置。由于隧道腔体的尺寸限制，电势电极的最大距离通常受到限制。因此，探测深度往往无法适当覆盖目标。另外，由于掌子面点电极源不易接近，只能在掌子面附近设置点电极源，点电极源激发的电信号无法与大深度的含水异常耦合。因此，传统的点电极法在隧道中进行正向探测存在探测深度小的缺点。为了通过增加探测深度来克服这个问题，首先使用水平钻孔铜套管作为新的长电极源阵列，这（据作者所知）在隧道前向探测中从未有过报道。我们开发了一种使用长电极源进行 3D 直流电阻率建模的新方法，用于使用有限元方法在隧道中进行正向探测。采用长电极电流源代替常规点电极电流源，将观测电位电极分别布置在隧道底板、隧道掌子面和水平钻孔内。全空间直流法长电极源的理论公式首次应用于隧道正向探测。使用长电极源的全空间模型的分析测试已用于验证 3D 算法的准确性。使用长电极源的三个合成地质模型通过研究预测异常的检测能力来检验其适用性。由于长电极源距离异常点较近，长电极源激发的视电阻率观测信号强于点电极源。这种使用长电极源的新方法大大提高了异常的分辨率，对于隧道施工的安全具有重要意义。
The direct current resistivity method has been widely used for the prediction of water‐bearing structures in subway tunnels and mine tunnels. The traditional direct current resistivity uses point electrode sources in tunnels to excite the electric field; potential electrodes are arranged on the back of the tunnel face to measure the position of the anomaly using the apparent resistivity sounding curve. Due to the dimension limitations of the tunnel cavity, the maximum distance of potential electrodes is often restricted. Thus, the exploration depth often cannot cover the target appropriately. Additionally, owing to the inaccessibility of point electrode sources on the tunnel face, point electrode sources can only be set near the tunnel face, so the electric signal excited by point electrode sources cannot be coupled with the water‐bearing anomaly at a large depth. As such the traditional point electrode method for forward probing in tunnels has a shortcoming of small detection depth. To overcome this problem by increasing the detection depth, a horizontal drilling copper casing is first used as a new long electrode source array, which (as far as the authors are aware) has never been reported in forward probing in tunnels. We developed a new method of 3D direct current resistivity modelling with a long electrode source for forward probing in tunnels using the finite‐element method. The long electrode current source was used to replace the conventional point electrode current source, and the observed potential electrodes were respectively arranged in the tunnel floor, tunnel face and horizontal drilling. Theoretical formulas for the long electrode source for the whole‐space direct current method are first applied in forward probing in tunnels. An analytical test for a whole‐space model with the long electrode source has been used to validate the accuracy of the 3D algorithm. Three synthetic geological models for the long electrode source were used to examine the applicability by investigating the detection capability to predict the anomaly. The observed signal of apparent resistivity excited by the long electrode source is stronger than that of the point electrode source because the long electrode source is closer to the anomaly. This new method using the long electrode source greatly improves the resolution of the anomaly, which is of great significance for the safety of the tunnel construction.