Using BHR to detect coal seam interface in coal mine

The geological transparency of working face is the premise and guarantee to realize the intelligent and accurate mining for coal resources. A large number of gas drainage holes, water exploration holes and other boreholes are constructed before and during coal mining. In this paper, the borehole radar (BHR) is used to detect the coal bedding interface in boreholes along the coal seam. With gprMax, we analyze the conditions of the top and bottom interface of coal bedding with 100 MHz and 200 MHz BHR at an dip angle of 0°;analyze the response characteristics of the 200 MHz BHR when the dip angle is 15°, 30°, 45°, and 60°;analyze the influencing characteristics of roadways and bolts during BHR detection.Practical applications are carried out.The result shows that 1) when the borehole inclination is 0°, to distinguish the reflected wave of roof from that of floor, for 100 MHz borehole radar, ΔD needs to be greater than 1 m, and for 200 MHz borehole, it needs to be greater than 0.5 m. 2)When the drilling inclination angle is not 0°, the reflection profile of the top and bottom interface will have a cross feature, and the greater the dip angle, the greater the crossing angle. 3) BHR multiples in boreholes along coal seam have nothing to do with borehole position and inclination angle, but are related to dominant frequency of BHR;4)The change of aperture mainly affects the in-phase axis shape of direct wave. 5)the roadways and bolts have an impact on the detection of coal -rock interface.6)The position of roadway reflection event axis is only related to the nature of coal seam. Therefore, the electromagnetic wave velocity of the coal seam can be calculated by calculating the slope of the event axis. The actual detection of coal seam thickness of about 3 m using 200 MHz in a mine in Shanxi province shows that the electromagnetic wave propagation speed in the coal seam in this area is 0.1342 m/ns. With the proposed processing method,the accuracy of BHR results is high, the error is within 0.5 m.Combined with the borehole trajectory, the BHR can provide accurate coal seam interface position information for the transparent working face.