等值反磁通瞬变电磁法在浅部岩溶探测中的应用研究——以惠州市龙门县某地区为例

Application of equivalent inverse flux transient electromagnetic method in shallow karst detection--Taking an area in Longmen County,Huizhou City as an example

传统瞬变电磁法受关断时间和互感的过渡过程影响,存在较大浅部盲区;新近发展迅速的等值反磁通瞬变电磁法从理论和仪器上实现了纯二次场的观测,大大提高了浅部区域的探测精度。为研究等值反磁通瞬变电磁法在100 m以浅岩溶探测的应用效果,以惠州市龙门县某岩溶发育区为靶区,开展了方法有效性研究,取得主要成果与结论:(1)界定的土石界面和圈定的岩溶发育区与已知钻孔揭露情况吻合较好,验证了基于等磁反磁通瞬变电磁法在100 m以浅岩溶探测的有效性;(2)反映区内岩溶具有一定连通性,岩溶大小约1~20 m,岩溶主要发育于20~40 m及60 m以下埋深。研究结果一方面有效圈定了研究区100 m以浅岩溶发育区,对后续桥梁工程的安全建设具有重要意义;另一方面等值反磁通瞬变电磁法具有施工便捷、采集高效、抗干扰强等优势,未来有望在城市浅部空间探测领域实现更大作为。

The traditional transient electromagnetic method is affected by the transition process of turn-off time and mutual inductance,and there exists a large shallow blind area;the newly developed equipotential inverse flux transient electromagnetic method realizes the observation of pure secondary field theoretically and instrumentally,which greatly improves the detection accuracy in shallow areas.In order to study the application effect of isomagnetic inverse flux transient electromagnetic(IATEM)method in the shallow karst detection of 100m,a karst development area in Longmen County,Huizhou City,was taken as the target area to carry out the method effectiveness study,and the main results and conclusions were obtained:(1)The defined soil-rock interfaces and the circled karst development area match well with the known drilling exposure,which verifies the validity of the isomagnetic inverse flux transient electromagnetic(IATEM)method in the shallow karst detection of 100m;(2)Reflects that the karsts in the area have a certain connectivity,the size of karsts is about 1~20 m,and the karsts are mainly developed in the depths of 20~40 m and below 60m.The results of the study have effectively defined the karst development area in the study area with a depth of 100m and a depth of 60m or less.On the one hand,the results of the study have effectively defined the shallow karst development area in the study area of 100m,which is of great significance for the safe construction of the subsequent bridge project;on the other hand,the equivalent antimagnetic flux transient electromagnetic method has the advantages of convenient construction,efficient acquisition,strong anti-interference,etc.,which is expected to be more important in the future in the field of urban shallow space exploration.