ABSTRACT Tunnel forward geological prediction is indispensable to tunnel construction. The transient electromagnetic method is widely used in the field of tunnel forward geological prediction. A small fixed‐loop transient electromagnetic method adapted to the limited space of a tunnel face is proposed for tunnel forward geological prediction for the first time. This method makes use of a large number of non‐central points inside the loop. The obtained numerical simulation and field data show opposite trends owing to mutual inductance and self‐inductance. A correction method for the field value of non‐central points is proposed. The influences of different parameters are verified and the correction function is established by a test method. The validity of the correction function is verified through controlled field tests. The small fixed‐loop transient electromagnetic has been successfully applied to a tunnel under the Weiwu expressway. This method can effectively improve the detection depth and better detect unfavourable geological bodies, such as karsts in front of the tunnel face.

中文翻译：

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隧道前向地质预测中的小固定环暂态电磁波

摘要 隧道前向地质预测是隧道施工必不可少的。瞬态电磁法广泛应用于隧道正向地质预测领域。首次提出了一种适用于隧道掌子面有限空间的小型固定回路瞬态电磁法进行隧道前向地质预测。这种方法利用了循环内的大量非中心点。由于互感和自感，获得的数值模拟和现场数据显示出相反的趋势。提出了一种非中心点场值修正方法。验证了不同参数的影响，并通过测试方法建立了校正函数。校正功能的有效性通过受控现场测试进行验证。小型固定回路瞬态电磁已成功应用于魏武高速公路下的某隧道。该方法可有效提高探测深度，更好地探测出掌子面前方岩溶等不利地质体。