Electrical monitoring of overburden failure in hard roof working face with thick loose layer and thin bedrock

It is of great significance to grasp the development height of water conduction fracture zone for safe mining of the working face in thick loose layers and thin bedrock coal mines. Before the influence of coal seam mining, a lift hole was constructed in the roadway of the working face to the roof of coal face, and the electrode cables in the holes were arranged to form a borehole electrical monitoring system. Parallel electrical instruments and drilling cables were connected in the roadway, and AM method was employed as the data acquisition method. With the position of coal mining face gradually approaching and entering the drilling control range, the changes of electrode current and apparent resistivity were monitored. The results of electrical monitoring on the working surface of the hard roof of thick loose layer and thin bedrock in Panbei Coal Mine show that the electrode current values and apparent resistivity values in curved subsidence zone are relatively stable and are less affected by mining; in the water-conducting fracture zone, the current value of electrodes decreases significantly and the apparent resistivity value increases accordingly. At the roof height of 0 ～ 40m, the influence range of mining advance can reach 410 m or so; the hard roof sandstone stratum is the key stratum to control the overburden rock failure, and the hard roof rock stratum above the gob collapses and the working face is 9-16m lagging behind; the height of the water-conducting fracture zone in the working face is 37 m, the water-conducting fracture zone does not develop to the bedrock surface, and the weathered sandy mudstone fractures are closed under the action of mining stress.