Monitoring and Law Analysis of Surface Secondary Subsidence of Closed Mines in Huainan Mining Area Based on InSAR

Objectives: As a continuation of mining subsidence, the surface secondary subsidence (including sinking and uplift) of closed mines poses a potential threat to the safety of surface buildings-structures in mining areas. However, at this stage, the law analysis of the surface secondary subsidence of closed mines under different geological mining conditions is not yet comprehensive. Due to the high underground water level, thick Quaternary loose layers, and multiple coal seams in the Huainan mining area, monitoring and analyzing the surface secondary subsidence of closed mines in the Huainan mining area has important theoretical and practical values. Methods: In order to verify the reliability of the monitoring results, the StaMPS software was employed to simultaneously perform Persistent Scatterers interferometry (PSI) and Small Baseline Subset (SBAS) processing. Amplitude dispersion index and amplitude difference dispersion index were used to select coherent points, respectively. Then, the unwrapped phases of the coherent points were obtained by a three-dimensional phase unwrapping algorithm. Finally, the surface subsidence of the coherent points was obtained by using temporal-domain low-pass and spatial-domain high-pass filtering. Results: The results show that:(1) the surface uplift after the closure of the Xinjisan and LizuiziXinzhuangzi-Xieyi mines, with a maximum uplift rate of +51.1mm/a, and is located in the Xinzhuangzi mine, while the surface of Panyi mine is still sinking due to its late closure in September 2018. (2) The surface secondary subsidence law of closed mines in Huainan mining area is sinking stage → stable stage → uplift stage, which is consistent with the surface subsidence law of closed mines in Xuzhou mining area, but the sinking, stable and uplift stages do not necessarily occur successively over time. (3) There may be a hydraulic connection between the Lizuizi, Xinzhuangzi, and Xieyi mines. The groundwater first rises from the junction of Xinzhuangzi and Xieyi mines and then flows to the southeast and northwest sides. Conclusions: Although the law of surface subsidence in the closed mines of Huainan and Xuzhou mines is relatively consistent, there are differences in the law of surface uplift due to different hydrogeological mining conditions. Therefore, in future work, we will continue to pay attention to the law of surface secondary subsidence of closed mines under different geological mining conditions.