瞬变电磁法勘探煤矿不同层间距双层积水采空区的可行性研究

Feasibility of the transient electromagnetic method in the exploration of double-layer waterlogged goafs with different layer spacings in coal mines

利用瞬变电磁法勘探上下重叠的双层积水采空区的难度较大,上部积水采空区会阻碍电磁场的传播,增加下部积水采空区的观测时间,降低信噪比,而双层积水采空区的埋深和层间距也会影响瞬变电磁信号的观测时间以及信噪比。为此,以山西马家岩煤矿为工程背景,构建了双层积水采空区模型,分析了层间距分别为25、50、75、100 m的双层积水采空区的电磁场传播过程及所需要的观测时间;使用均方根误差对不同层间距双层积水采空区的感应电压之间的差异进行了定量表述,并基于观测过程中的记录误差以及噪声水平提出下层积水采空区可勘探的判别标准。物理模拟实验结果表明:4种模型的感应电压值的差异主要集中在晚期,并且随着层间距和上层积水采空区埋深的增大,感应电压值的差异减小,层间距为75 m时感应电压之间的差异接近噪声水平;在马家岩煤矿对层间距为75 m的双层积水采空区进行了实际探测,结果表明下部积水采空区没有得到有效识别。因此,可以认为层间距大于75 m时下部积水采空区难以得到识别。

It is difficult to explore the overlapping double-layer waterlogged goafs using the transient electromagnetic method.The rea-son is that upper waterlogged goafs will hinder the propagation of the electromagnetic field,thus prolonging the observation of the lower waterlogged goafs and reducing the signal-to-noise ratio.Besides,the burial depths and layer spacings of double-layer waterlogged goafs affect the signal-to-noise ratio and the observation time of transient electromagnetic signals.By building a double-layer waterlogged goaf model based on the Majiayan coal mine in Shanxi,this study analyzed the electromagnetic field propagation under layer spacings of 25 m,50 m,75 m,and 100 m,and calculated the observation time of waterlogged goafs with different layer spacings.Furthermore,it quantitatively characterized the differences between induced voltages in the double-layer waterlogged goafs with different layer spacings using root mean square errors.Additionally,this study proposed the identification criteria for explorable lower waterlogged goafs based on the record errors and noise levels during the observation.The results of physical simulation experiments are as follows:The differ-ences between the induced voltages of double-layered waterlogged goafs with different layer spacings occur mainly in the late stage;the differences between induced voltages gradually decrease as the layer spacing and the burial depth of upper waterlogged goafs increases;the difference between induced voltages is close to the noise level when the layer spacing is greater than 75 m.The actual detection of the double layer waterlogged goaf with a spacing of 75 meters was conducted in Majiayan Coal Mine,and the results showed that the lower waterlogged goaf was not effectively identified.Therefore,It is difficult to effectively explore the lower waterlogged goafs when the layer spacing is greater than 75 m.