Response of Electrical Advanced Detection of Eight-point Sources-based Method while Excavating for the Geological Anomalies in front of the Tunnel
In order to reliably detect the geological anomalies in front of the excavation roadway,a eight-point source-based electrical advanced detection technology while excavating has been proposed.A 32-electrode observation system is arranged along the middle line of the side of the roadway from the head-on to the back,with adjacent electrode distance of 5m.The 8 electrodes near the working face are used as the point power electrodes sequentially,and apparent resistivity values of the monopole-dipole device of the entire measurement line are collected.According to the principle of the differential electric sounding,the apparent resistivity values measured by each point source can be regarded as the electrical sounding results,and the eight-point source electrical sounding curve and apparent resistivity imaging map can be obtained.For every 20m of tunnel excavation,the last 4 electrodes are rolled and arranged to the front 4 electrodes of the new survey line.Then,eight-point source electrical sounding data collection is carried out to obtain continuously changing electrical sounding curves and imaging results.According to the apparent resistivity response formula of the unipolar-dipole device,the response of the geological anomaly sphere in the leading direction of the working face is calculated,and the results show that for the same geological anomaly sphere,the resistivity response becomes more and more obvious from far to near from the excavation face.When the distance from the edge of the low-resistance sphere to the point source is not greater than the radius of the sphere,it can be explored;When the distance from the edge of the high-resistance sphere to the point source is not more than 1/2 of the radius of the sphere,it can be explored;The response of a low-resistivity sphere is stronger than that of a high-resistivity sphere.The larger the radius of the geological anomaly,the greater the advance distance that can be detected.Therefore,the detection accuracy of geological anomalies in the range of 0～50m ahead is high.The reliability of geological anomaly detection in the range of 50～100m ahead is low,and it is suitable to explain whether there is a large range of geological anomaly areas.The eight-point sources-based method while excavating can reliably detect the occurrence of geological anomalies in front of the working face,and provide geological guarantee for the safe and rapid excavation of the working face.
mine tunnelselectrical advanced explorationgeological anomaliesapparent resistivitydetection while excavating
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