The height of water-conducting fractured zone is an important indicator for ensuring safe mining of coal resources under water bodies. In view of the problems and deficiencies to quote empirical formula for top coal caving in thick coal seams, the basis of the empirical formula is analyzed and the applicable conditions, which are large mining areas, single-layer mining thickness of 1~3 m, and cumulative mining thickness not exceed 15 m for coal seam slice mining, are clarified and emphasized. Based on the field measurement results of the top coal caving property and top coal recovery rate, the concept of effective mining thickness for top coal caving in thick coal seams is proposed. The effective mining thickness is closely related to the recovery rate of the top coal caving and the height of the water-conducting fractured zone increases with the increase of the effective mining thickness. It is shown that the height of the water-conducting fractured zone based on the effective mining thickness can effectively avoid the underestimation caused by the increase of the top coal recovery rate in top coal caving. Based on the evolutionary law of the overburden and surface subsidence from subcritical to critical or supercritical mining, the Boltzmann function is introduced to express the relationship between the critical mining degree and the height of water-conducting fractured zone. A method for calculating the maximum height of the water-conducting fractured zone is provided based on the degree of critical mining. Taking fully into account of the recovery rate of the top coal caving and the degree of critical mining, a technical reference is provided for scientifically calculating the maximum height of the water-conducting fractured zone in thick coal seam top coal caving and the safe mining under water bodies or aquifers can be ensured.

Remote sensing monitoring of methane emissions in coal mines has become a major field of research in the global efforts to monitor potent greenhouse gas emissions. While existing studies predominantly concentrated on the technological dimensions, this study proposes to review previous stu-dies, analyze major trends and pinpoint the current research priorities for this field of study. We retrieved domestic and international literature on remote sensing monitoring of methane emissions in coal mines since 2000 from Web of Science and China National Knowledge Infrastructure (CNKI) databases via keyword searches. A visualized bibliometric analysis was then conducted using the CiteSpace tool. Results show that research on remote sensing monitoring of methane emissions in coal mines exhibited significant growth, with an average annual increase of 20 %. We identified the evolving trends of leading countries, research institutions, and research domains with top research contributions and proposed intermediary centrality metrics that reflect patterns of international collaboration: The United States (181 articles) and China (98 articles) are the 2 leading countries with the highest contributions of publications, followed by Germany and Canada; The National Aeronautics and Space Administration (NASA) ranks the first among research institutions with 66 publications, while the Chinese Academy of Sciences ranks the fifth globally; Satellite remote sensing, methane concentration retrieval, methane quantification, and intelligent data processing are the current research priorities in this field; International studies focus more on global methane emission monitoring and policy-driven technological innovations while domestic studies excel in monitoring and intelligent management of methane emissions in coal mines; Co-citation analysis revealed that advancements in high-resolution remote sensing and retrieval technologies have significantly enhanced the spatial and temporal precision of methane emission monitoring. This study therefore suggests areas for future research, such as the precision and efficiency of remote sensing monitoring, intelligent data processing and algorithms, multi-platform integration and fusion, and international collaboration and data sharing.