大定源瞬变电磁法在何家地隧道煤炭采空区中的应用

Application of Large Fixed Loop Transient Electromagnetic Method on Coal Mined-out Area in Hejiadi Tunnel

大定源瞬变电磁工作效率高,信号强度大,横向分辨率高,在生产实践中,一般采用中心回线晚期视电阻率,进行定性解释。为了更好地配合地质钻探查探何家隧道的煤炭采空区情况,初步采用大定源瞬变电磁装置进行现场实验。结合实际工作所需探测深度,对装置参数进行相关实验;为了提高工作效率,作业区域在回线中心三分之一范围内测量。这样导致不满足晚期条件,早期道视电阻率计算结果偏大;当勘探区距离回线边框较近时受一次场不均匀影响,存在“边界效应”。因此提出对早期、晚期数据进行分开处理,早期道数据采用早期视电阻率公式,晚期道采用晚期视电阻率公式,根据现场发现,数据处理和实际地质情况吻合的很好。

Large fixed loop transient electromagnetic method has high work efficiency,and high signal strength,and high lateral resolution,the central loop advanced apparent resistivity were generally adopted in the production practice for qualitative interpretation.The large fixed loop transient electromagnetic method is selected preliminarily for field experimentation in order to better fit the geological drilling exploration of coal mined-out area in Hejiadi tunnel. The relevant experiments were carried out for device’s parameters combining with the required detection depth;the operation area within the range of one-third of the loop center in order to improve the working efficiency. But the above mentioned method of work can not meet the later conditions,and the calculation results of early apparent resistivity were larger;the “boundary effect” exists when the exploration area and loop border is very closed and which shall be affected unevenly by the primary field. Therefore it is proposed that the early,late data shall be treated separately,the early apparent resistivity formula shall be used for the early data,the late apparent resistivity formula shall be used for the late data,according to the onsite feedback,the data treatment is well matched to the actual geology reality.