Research status and prospect of secondary subsidence in closed mine

The closed mines are a large number and widely distributed in our country. After the mine is closed,the drainage will be stopped and the groundwater level will rise. Affected by the groundwater,the overburden and surface will sink again,endangering the safety of buildings,traffic,power,communication,and other infrastructure,and the stability of the construction site above and around the closed mine. Therefore,studying the mechanism,law and the prediction method of surface secondary subsidence in closed mine has important theoretical and practical significance. Based on the collection of relevant literature at home and abroad,combined with the monitoring results of surface secondary subsidence of closed mines in the eastern and western mining areas of Xuzhou,this paper systematically reviews and analyzes the research status and existing issues of monitoring methods,formation mechanism,temporal-spatial distribution law,and predic〖LM〗tion methods of surface secondary subsidence of closed mines. Firstly,the advantages and disadvantages of conventional ground deformation monitoring methods and aerospace measurement methods are compared,and the superiority and defect of Interferometic synthetic Aperture Radar(InSAR)technology in surface subsidence monitoring of closed mines are summarized; Secondly,based on a large number of measured data at home and abroad,the formation mechanism and temporal-spatial evolution law of overburden and surface secondary subsidence in closed mines are analyzed and summarized,the main inducing factors of overburden and surface subsidence are obtained,which are the deformation or instability of mining fractured rock mass,overburden structure and coal (rock)pillar under the action of groundwater; The main inducements of overburden and surface uplift are that with the rise of groundwater level,the pore pressure acting on mining fractured rock mass and Quaternary loose layer increases,and the effective stress decreases,resulting in elastic recovery deformation,and the expansion of swelling rock mass in groundwater may also lead to overburden and surface uplift; The secondary subsidence of closed mine can be divided into five stages in time:①initial stable stage;②subsidence stage;③intermediate stable stage;④uplift stage;⑤final stable stage,and the influence of different mining methods and multi coal seam mining on the temporal-spatial distribution law of surface subsidence of closed mines is analyzed. On this basis,based on the constitutive relationship of mining fractured rock mass,the prediction models of surface subsidence and uplift of longwall caving mining,filling mining,and pillar mining are given respectively. Finally,we point out that the mechanism and law of overburden and surface subsidence of closed mine are very complex physical and mechanical processes,involving geological mining environment,mining fractured rock mass and overburden structure,constitutive relationship,deformation characteristics,water-rock coupling,groundwater dynamic effect,expansion deformation of swelling rock mass and other factors. The current research is preliminary,therefore,further research is needed.