FCTEM小回线瞬变电磁法在铁路桥梁基础勘查中的应用

Applicationof Small Loop Transient Electromagnetic Method in Geological Survey of Railway

关断时间长短直接影响瞬变电磁法的浅层探测能力,当发射磁矩相同时,关断时间越短,激发的一次场高频信号越强,丢失的早期信号越少,可缩短瞬变电磁法探测盲区,提升浅层探测能力。FCTEM(Fast Cut-off Transient Electromagnetic)小回线瞬变电磁法通过恒压钳位实现发射电流的高速线性关断,无损消耦实现一次场、二次场分离,大动态、高速采样实现纯净二次场采集。工程实例证明,FCTEM小回线瞬变电磁法具有施工便捷高效、分辨率高、盲区小、探测深度大、抗噪声能力强等优势,FCTEM拖曳式高分辨瞬变电磁系统能有效解决浅层盲区的技术瓶颈,对于填充性溶洞优势明显,能够清晰分辨地表10 m以浅的直径不足1 m的小型溶洞以及50 m以内的小型断层。

The length of turn-off time directly affects the shallow detection ability of transient electromagnetic(TEM).When the transmitting magnetic moment is the same,the shorter the turn-off time is,the stronger the high frequency signal of the primary field will be,and the less the early signal will be lost,which can shorten the blind area of TEM detection and improve the shallow detection ability.Fast cut-off small loop transient electromagnetic method realizes high-speed linear turn-off of emission current through constant pressure clamping,achieves non-destructive decoupling to separate primary field from secondary field,and achieves pure secondary field acquisition with large dynamic and high-speed sampling.The engineering examples indicate that the fast cut-off small loop transient electromagnetic method has the advantages of convenient and efficient construction,high resolution,small blind area,large detection depth,strong anti-noise ability and so on.FCTEM system can effectively solve the technical bottle neck of shallow blind areas,and has obvious advantages for filling karst caves.It can clearly distinguish small karst caves with a shallow diameter of less than 1m on the surface and small faults within 50 m.