Research On Extraction Of Subsidence Information In High Phreatic Coal Mining Area

The rapid acquisition of surface subsidence information in coal mining areas is of great significance for the ground remediation and ecological restoration in mining areas.As a typical mining area in China,the main mining method is well mining,so coal mining is very easy to cause a large area of subsidence water and non-water subsidence area.How to obtain the complete subsidence information of the mining area has always been a hot issue.The complete acquisition of the subsidence information of the mining area is conducive to the local effective restoration work.The previous research work of mining subsidence mainly focused on single surface subsidence,most of the research areas are non-high phreatic coal mining areas,so only the surface deformation fluctuation of the mining area is obtained;with the increasing scope of water accumulation in high phreatic coal mining areas,more and more research focuses on monitoring the dynamic change of water accumulation,but the surface deformation of non water accumulation areas is lack of relevant research.In this study,Baodian coal mine in Jining City,Shandong Province was taken as the research area.Based on multi-source and multi temporal data,a variety of methods were used to obtain mining subsidence information.In this study,Landsat series data were used to obtain the information of subsidence water body in mining area.Based on the Modified Normalized Difference Water Index(MNDWI),an Enhanced Normalized Difference Water Index(E-MNDWI)was proposed for the water edge of coal mining subsidence which was easy to be confused with water information by adding short wave infrared band.Using Sentinel-1A data,the subsidence non water area was extracted by Small Baseline Subset Interactive Synthetic Aperture Radar(SBAS-InSAR).Finally,the two results were combined to obtain the subsidence range of the whole mining area and classify according to the subsidence situation,in order to provide theoretical basis for the ecological protection and reasonable treatment of the mining area.The results are as follows:(1)The subsidence water body of high phreatic coal mining area was affected by a large number of fly ash and coal gangue produced by mining area.After a variety of tests of index and threshold range changes,the E-MNDWI index was proposed by adding short wave infrared on the basis of MNDWI.The results showed that E-MNDWI can get the information of subsidence water more clearly,and effectively eliminate the impact of fly ash and vegetation around the water,so that the classification results were more accurate.The overall accuracy was more than 90%,and the Kappa coefficient was more than 80%.The universal research showed that E-MNDWI was also effective in distinguishing mountain shadows,extracting mountain water information and extracting plain water information.(2)The SBAS-InSAR technology can use Sentinel data to obtain the dynamic changes of the surface in the non-water subsidence area of the mining area.The accuracy of monitoring the surface deformation can reach millimeters.It can identify the surface deformation that can not be recognized by the naked eye,and it can predict the trend of the surface deformation in the later mining area and provide help for the prevention of subsidence.SBAS-InSAR technology can effectively solve the problems of time-space decorrelation and atmospheric delay,and has great potential in detecting long-term accumulated slow deformation.3)Using multi-source and multi-temporal data combined with various methods to monitor the surface deformation of high phreatic coal mining area,and comprehensively grasp the subsidence situation of the mining area.During the monitoring period,the subsidence area of the whole mining area was 10.1km~2,accounting for 28.45%of the mining area.The perennial subsidence area was 4.6 km~2,and the subsidence non-retention area was5.5 km~2.The western part of the whole mining area was dominated by subsidence water,the eastern and southern parts were still in a state of subsidence.The subsidence rate near Damachang in the east of coal mining area was the fastest,reaching 41.69 mm/a.The results of water extraction and SBAS-InSAR were interpolated by Kriging method,and the subsidence contour of the whole mining area was obtained.The isoline in the east of the mining area was sparse,which indicated that the subsidence gradient range was large.The isoline formed many subsidence funnels between the water bodies in the west,which indicated that the subsidence in the west was more intense.(4)According to the subsidence obtained during the monitoring period,the subsidence was classified according to the average annual subsidence after comprehensive consideration,and was divided into slight subsidence(0-10 mm),slight subsidence(11 mm-20 mm),and moderate subsidence(21 mm-30 mm)and severe subsidence(>31 mm and subsidence water area).Combined with the subsidence level and the actual situation of the mining area,the corresponding countermeasures were proposed,mainly including ecological restoration,land reclamation and village relocation.Using multi-source and multi-temporal data and combining with various methods to obtain mining subsidence information can provide theoretical basis for ecological restoration and land reclamation of coal mining cities,and provide new ideas for rapid and efficient monitoring of surface deformation in mining subsidence areas in the future.