针对岩溶发育地区隧道开挖时现有地质预报技术对岩溶突水较难做出准确预测的问题，设计出大断面三维多匝小回线瞬变电磁探测技术。依据岩溶发育特点，采用数值模拟方法对隧道掌子面前方25 m和50 m处不同体积富水溶洞进行模拟，研究掌子面前方不同距离和规模的低阻异常体瞬变电磁响应特征。基于数值模拟结果，在张吉怀铁路古丈隧道岩溶发育段进行探测验证，结果表明： 1）溶洞模型在二维视电阻率等值线断面图上25 m和50 m处形成闭合、视电阻值小于60 Ω·m的低阻区，低阻区与设计的模拟体的位置和范围一致； 2）大断面三维多匝小回线瞬变电磁探测三维显示结果与现场实际揭露情况基本吻合，采用该技术能够准确预报掌子面前方17~30 m、隧道两侧20 m到隧道中轴线的充泥含水溶洞。

It is difficult to accurately predict the karst water burst by existing geological prediction technology during tunnel construction in karst region. Hence, a transient electromagnetic detection technology with large crosssection fixedpoint and threedimensional multismallline is designed. And then according to the karst development characteristics, the caves with different sizes 25 m and 50 m ahead of tunnel face are simulated by numerical simulation method, and the transient electromagnetic response characteristics of lowresistance anomalous bodies with different sizes and distances from tunnel face are studied. Finally, the engineering practice is carried out in Guzhang Tunnel on ZhangjiajieJishouHuaihua Railway to verify the simulation results. The results show that: (1) A closed lowresistance region with apparent resistance value less than 60 Ω·m is formed 25 m and 50 m ahead of tunnel face on 2D apparent resistivity contour map; and then the position and range of the lowresistance region is in accordance with those of design models. (2) The results revealed by transient electromagnetic detection technology with large crosssection fixedpoint and threedimensional multismallline are basically consistent with the actual situations; and the karst 17-30 m ahead of tunnel face and 20 m from both left and right side of tunnel to axial line can be accurately predicted by the abovementioned technology.