Analysis of coal thickness identification and imaging accuracy of mine directional borehole radar

The geological structure of coal mines in China is complex, and precise detection of coal seam thickness and orientation is crucial for intelligent and safe mining operations. Conventional geophysical ahead-detection methods suffer from continuously expanding detection errors in coal-rock structure identification with increasing advance distance. Moreover, most borehole geophysical exploration equipment exhibits limited effectiveness in coal thickness identification due to inadequate directional capability. To address these challenges, a mine directional borehole radar is developed. Directional identification of coal seam thickness is realized through the integration of a directional radar antenna, a high-precision PWM motor speed control system, an angular and directional perception system, and positioning and calculation algorithms. A spatial relationship model between the directional borehole radar antenna and the target body is constructed, enabling precise perception of the target detection direction. The azimuth angle perception error is minimized to 1° (when motor speed is lower than 3.71 r/min). A study on coal thickness identification using directional borehole radar and imaging accuracy analysis is conducted to provide guidance for on-site radar operation and development of in-situ drilling detection equipment. Firstly, the working principle of the directional borehole radar and coal thickness detection method are systematically elaborated. Secondly, following clarification of the relationship between PWM duty cycle and motor speed, experiments with different PWM duty cycles are designed to study and analyze the impact of motor speed on acquisition accuracy. It is found that when data sampling accuracy error is within 2%, the optimal motor speed is 7.84 r/min. In view of the current situation where advancement speed of conventional mining drilling machines is approximately 0.01–0.30 m/s, a series of detection experiments with different advancement speeds ranging from 0.05–0.40 m/s are designed. The influence laws of detection speed on sampling accuracy and of collection accuracy on imaging accuracy are analyzed and clarified in detail. The experimental results show that under current tunnel drilling machine working conditions in mines, when the directional borehole radar acquisition speed is 7.84 r/min and detection advance speed is 0.05 m/s, the angle acquisition accuracy error rate is minimized to 2.8%, acquisition positioning accuracy of 97.2% is obtained, and target body identification resolution of 0.256 m is achieved. In mine measurement results, the coal-rock interface and depth and orientation information of the coal seam are detected by the directional borehole radar, with a coal thickness detection accuracy error of 3.15%. Effective technical support for mine geological transparency and intelligent construction of coal mines is provided through these research results.