Simulation Of Tridimensional Ground-tunnel Transient Electromagnetic Method On The Collapsed Column Of Heading Faces

The coincident loop device is widely used in mining transient electromagnetic advanced detection now,but limited by the emission current and tunnel space,it can not meet the need of the meticulous detection in deeper mining collapse columns.In view of this,this paper presents the tridimensional ground-tunnel transient electromagnetic method.Namely it establishes an artificial field source on the ground,while in the underground roadway the overlapping loop launches electromagnetic fieldat the same time,receiving electromagnetic field data on the ground..The tridimensional ground-tunnel transient electromagnetic method is put forward on the basis of the coincident loop device.This paper expounds the forms and working methods of the method.Based on the characteristics of the coal mine tunneling faces collapse column and physical modeling similarity criterion,this paper established the physical model,taking the hidden trapping pillar in the working face as an example,comparing the response of two devices.Simulation results show that:?1 Coils of the tridimensional ground-tunnel transient electromagnetic method have two signal sources,so the amplitude of primary field and induction potential is higher than the overlapping loop,the curve shape of two devices are similar,both single peak exception,and the peak point corresponds to the center of the anomalous body,having higher resolving power for smaller size;?2 When the abnormal body locats in front of the roadway through the coal seam,in the bedding direction,the signal intensity of the tridimensional ground-tunnel transient electromagnetic method is obviously larger than that of the downhole overlap loop device.The potential value in the direction of the top plate and the bottom plate is smaller,and the optimum coupling is achieved in the bedding direction;?3 When the abnormal body is in front of the roadway developing under the coal floor,the signal intensity of the tridimensional ground-tunnel transient electromagnetic method is stronger than that of downhole overlap loop device.However,the tridimensional ground-tunnel transient electromagnetic method is best coupled in the bedding direction,while the overlap loop has the strongest response in the bottom direction;?4 When the anomalous body is right in front of roadway through the coal seam,Both of work devices show a higher value on the right side than the left side,corresponding a low resistance anomaly to the forward right.The minimum value is near 4 or 5 point on the left,and at this time,the coil and the copper bar are in a plane approximately,having the weakest induction signal,which determines the direction of the abnormal body.The tridimensional ground-tunnel transient electromagnetic method is better coupled in the direction of the bedding and the bottom,and the amplitude of the overlap loop device is smaller and prone to jitter in the late stage.In this paper,COMSOL simulation software is used to simulate the collapse column through the coal seam in front of the tunnel.The results show that both of two devices have unimodal anomaly,and the maximum value points correspond to the abnormal position accurately.However the tridimensional ground-tunnel transient electromagnetic method has higher signals and more obvious features,with the best coupling effect in the roof and the bedding direction,the weakest signal in the bottom direction.The tridimensional ground-tunnel transient electromagnetic method has more abnormal response and more remarkable characteristics for the long distance collapse column,while the overlap loop device achieves the best coupling in the bedding direction.All of the above are basically consistent with the physical simulation results.