Detection of hidden mining-induced ground fissures via unmanned aerial vehicle infrared system and ground-penetrating radar

We propose a new combined detection method for the hidden ground fissures using unmanned aerial vehicle (UAV) with infrared camera and ground-penetrating radar (GPR) and applied it in the panel No. 12203 of the Daliuta coal mine. Subsequently, the extensive UAV aerial photography was taken to obtain the ground surface temperature of the entire longwall panel. The GPR detections along three survey lines in the selected ground surface zone of interest were carried out to find the positions of hidden ground fissures induced by underground mining. Based on the temperature measurement and analysis, the temperature of the surface above the hidden ground fissure is higher than that of the surface in non-fissure zone. The location of the hidden ground fissure can be determined by selecting the zone with a surface temperature higher than the temperature threshold, which is equal to the maximum average temperature of each surface zone. The similar track of hidden fissures can be drawn by GPR detection. The hidden ground fissure, with longitudinal lengths of 1–5 m and staggering horizontal lengths of 1–3.5 m, is mainly distributed 20–50 m in front of the working face, and between the step-like fissures. As the working face advances, the hidden ground fissure is recoverable with a cyclic evolution of formation, longitudinal development, and pinch-out. The optimal period for fissure detection is 9:20 a.m. to 11:30 a.m. at the environmental condition of this study, during which the open fissure has the lowest temperature range compared with the ground surface and vegetation. The results show that the proposed synergistic method can efficiently and accurately locate the hidden ground fissures and explain the distribution mechanism of ground temperature values in the mining area.