Research on several fundamental issues of coal mining subsidence control in plain coal mining area of the Lower Yellow River

The lower of the Yellow River Basin flows through Henan and Shandong Province, and its landform is mainly alluvial plain.The area is not only the main grain-producing area in China, but also an important coal base.The major eco-environmental problem in plain coal mining area is subsidence and serious water accumulation, resulting in the decrease of cultivated land area and deterioration of the ecological environment.Taking the coal mining subsidence area in the lower Yellow River plain as the research object, the three basic problems in the control of coal mining subsidence area are discussed, such as the coverage of control, water-ponding mechanism and stability analysis, and studies on the control strategy.The research shows that:① The control coverage of coal mining subsidence area is a hidden information, which is difficult to identify accurately.The coverage is too large with the subsidence boundary of 10 mm.The damage boundary of subsidence buildings and cultivated land should be taken as the control coverage of coal mining subsidence.The damage to the building is usually determined by the critical deformation values(i=3 mm/m, ε=2 mm/m, K=0.2 mm/m²),and the boundary of cultivated land damage should be delineated by the minimum of the critical vertical subsidence value, the critical tilt deformation value and the critical horizontal deformation value.The calculation method of the deformation value and the delineation method of the control coverage are put forward.② Water-ponding in coal mining subsidence area is the main characteristic of ecological damage in plain mining area and the key to optimize control technology.It is related to factors such as surface subsidence, groundwater level, climate, soil structure, texture and so on.The mechanism and dynamic process of water-ponding after subsidence is expounded by clarifying the relationship between surface and groundwater level.③ The stability of the subsidence is the key to select control measures and timing.The method for analyzing the stability of subsidence is proposed based on the stage of control and considering the influence of surrounding and multi-seam mining.④ Regarding the serious damage of cultivated land in coal mining areas in the lower reaches of the Yellow River, the traditional “end management concept” and “zero-sum game thinking” should be discarded.Therefore, “the coordinated development strategy of coal mining and cultivated land protection” and “concurrent mining and reclamation strategy” are put forward, which can effectively protect and restore the cultivated land and realize the coordinated development of coal mining and ecological protection.