Advances and Future Directions in Monitoring and Predicting Secondary Surface Subsidence in Abandoned Mines

In recent years, the prolonged exploitation of natural resources has led to the depletion of reserves in some mining areas, resulting in the closure of mines worldwide. After mine closures, the fractured rock masses in abandoned mine cavities undergo weathering and degradation due to factors such as stress and groundwater, leading to reduced strength. This change alters the stress distribution and load-bearing capacity of the fractured rock within the abandoned voids, resulting in secondary or multiple deformations on the surface, which pose significant potential threats to surface infrastructure and public safety. Research into the mechanisms, patterns, and predictive methods of secondary surface subsidence in closed mines is thus of great theoretical and practical significance. Based on literature review and practical monitoring experiences in closed mine sites, this study systematically examines and analyzes the current state of surface secondary subsidence monitoring methods, formation mechanisms, spatiotemporal distribution patterns, and prediction methods in closed mines, as well as existing challenges. Initially, we compare the advantages and limitations of conventional surface deformation monitoring techniques with remote sensing techniques, emphasizing the benefits and issues of using InSAR technology. Next, by reviewing extensive data, we analyze the formation mechanisms and spatiotemporal evolution of overburden and surface secondary subsidence in closed mines. Building on this analysis, we discuss numerical and analytical methods for predicting secondary surface subsidence mechanisms in closed mines, evaluating the strengths and weaknesses of each approach. Predictive models for surface subsidence and uplift phases in the longwall collapse method are presented based on the constitutive relationships of fractured rock masses. Finally, the study highlights that the mechanisms and patterns of overburden and surface subsidence in closed mines represent a highly complex physical-mechanical process involving geological mining environments, fractured rock structures, constitutive relations, deformation characteristics, hydro-mechanical interactions, and groundwater dynamics, underscoring the need for further in-depth research. The conclusions are proved by some coal mining cases in China.This research has been supported by grants G2HOTSPOTS (PID2021-122142OB-I00), STONE (CPP2021-009072) and Defsour-PLUS (PDC2022-133304-I00) from the MCIN/AEI/10.13039/501100011033/FEDER, UE with funds from NextGenerationEU/PRTR.