Key technology of human environment and ecological reconstruction in high submersible level coal mining subsidence area:Acase study from Lüjin Lake, Huaibei

The formation of coal mining subsidence areas with high ground water levels in eastern China represented by Huainan and Huaibei has seriously affected the sustainable development of coal resource-based cities. In particular, the abandonment of water and soil resources, the disorder of ecosystem and the deterioration of living environment in the coal mining subsidence area have seriously hindered the economic and social development and the construction of ecological civilization. In order to solve problems of ecological restoration and sustainable development of coal resource-based cities, the evolution law and ecological damage characteristics of surface subsidence ponding are analyzed firstly. Based on the principle of mining subsidence and the theory of integration of mining and recovery, a dynamic prediction method of surface subsidence ponding is proposed, and a mathematical model of terrain reconstruction in subsidence area is constructed. The key technologies of mining and reconstruction, water circulation and water resources regulation, building zoning design, soil and water loss control and matrix improvement, and water land composite ecosystem reconstruction have been developed. At last, a new model of integrated management of human settlements and ecology in the coal mining subsidence area in the city is explored, and taking the subsidence area of Lüjin Lake in Huaibei as the engineering background, the engineering practice is carried out. The result shows that the accurate prediction of surface subsidence ponding depth, ponding area, ponding volume and maximum storage capacity at any time can be realized by integrating Knothe time function and water balance principle, and the maximum relative error is 9.7%. According to the earthwork balance condition, the pre-mining terrain reconstruction model is established, and the subsidence control area is divided into four excavation and filling areas centered on the center of the surface subsidence basin and symmetrical on both sides. The idle time of land is shortened from 14 months to 8 months, which provides a theoretical basis for the advanced treatment of coal mining subsidence in a high ground water level area. A complete set of key construction technologies such as environmental protection dredging water return and constructed wetland tail water treatment system, integrated mechanical deep drying system of sediment, multi-stage assembled water return system of high filling cofferdam is developed, which increase the water return efficiency by 17% and saved 5 260 square meters of sludge dump area. The zoning control technology of “flat building slope soil and water conservation shallow water aquatic vegetation deep water ecological fishery” is proposed, which realizes 100% efficient utilization of the water and soil resources in subsidence area. Combined with major livelihood projects such as diverting water from the Yangtze River to the Huaihe River, ecological corridor and green gold city, a new model of comprehensive treatment of coal mining subsidence areas integrating market operation, scientific restoration and sustainable operation is explored, which provides a theoretical basis and technical reference for ecological environment treatment and sustainable development of coal mining subsidence areas in the city.