Study On Subsidence Law And Monitoring Accuracy Of High Underground Water Level Coal Mining Areas Based On D-InSAR

Underground coal mining in high underground water level coal mining areas often causes large scale surface subsidence,and the characteristics of surface subsidence are quite different under different mining conditions and different coal occurrence conditions.Therefore,coal mining subsidence monitoring is carried out in high underground water level coal mining area,revealing the law of surface subsidence is of great significance to the sustainable development of economy and society and ecological restoration in this area.This paper takes the Juye mining area in the high underground water level coal mining area of Heze City,Shandong Province as the study area,and investigates the mining situation of the working face in the Juye mining area from 2018 to 2020.A total of 4 representative working faces are selected according to mediumthickness and thick coal seam.Secondly,54 pieces of Sentinel-1 radar satellite image data were selected for D-InSAR processing by the “two-track method”,and the deformation map of each period was obtained through band math and accumulation.The subsidence stage is divided by the subsidence velocity of the maximum subsidence point on the surface.Based on the analysis of the variation characteristics of the subsidence stage and the spatio-temporal evolution law,the influence of different mining geological conditions on the subsidence stage is ascertained.Finally,by dividing different subsidence areas,the D-InSAR deformation variable is compared with the field monitoring data to analyze the monitoring accuracy of the subsidence stage in different subsidence areas of the working face.The results showed that:(1)The main source stage of the maximum cumulative subsidence of the working face and the duration of surface movement is the active period,accounting for 80.73% and 58%respectively.In this stage,the surface subsidence movement is active,and the maximum subsidence speed can reach 6.8 mm /d or more,under the condition of continuous advancement of the working face,the subsidence and time of duration in the weakening period are greater than that in the initial period,and the parameters of each subsidence stage in the thick coal seam working face are greater than those in the medium-thick coal seam working face.(2)The spatio-temporal evolution law of working faces is universal: in the initial period,the subsidence of each working face is small,and the subsidence characteristics are not obvious.In the active period,the subsidence funnel begins to develop at the position of the incision,and the scope of subsidence influence continues to expand.The subsidence of the subsidence center increases continuously and moves with the advancing direction of the working face,and finally stops at the center of the working face.The regional subsidence tends to be stable during the weakening period,but the subsidence center area shows a "decreasing subsidence" trend,the subsidence area continues to expand.Under the condition of not being affected by the river,each working face finally forms a symmetrical subsidence basin.In addition,under the premise of using the Jenks method to divide the subsidence gradient,the subsidence funnels with different subsidence gradients can be used as a sign to judge that the working face with different coal seam thickness has entered the active period.(3)The impact of different mining geological conditions on the subsidence stage is more obvious.The inclination length of the working face,the thickness of the coal seam,the working advance speed and the depth of the coal seam are the key factors affecting the surface subsidence.The degree of influence of the subsidence stage in different mining geological conditions: the length of the working face > the thickness of the coal seam > the speed of work advancement > the buried depth of the coal seam > the long direction of the working face > the dip angle of the coal seam;the degree of influence of the parameters of the subsidence stage:the amount of subsidence in the weakening period > the duration of surface movement > Active period cycle > Active period sinking amount > Maximum sinking amount.In addition,compared with the thick coal seam working face,the medium-thick coal seam working face has a higher mining degree,and the depth-thickness ratio has a negative correlation with the subsidence coefficient.(4)After dividing different subsidence areas,it is found that the overall monitoring accuracy of the medium-thick coal seam working face is higher,the monitoring accuracy of the subsidence center area is higher than that of the subsidence margin area,and its different subsidence stages also maintain a high monitoring level,R2 is above 0.835.While the overall monitoring accuracy of the thick coal seam working face is inferior to that of the medium-thick coal seam working face,and the monitoring accuracy of the subsidence marginal area is better than that of the subsidence center area,except that the monitoring accuracy of the subsidence center area during the active period needs to be improved,other subsidence stages R2 is above0.874,achieving more accurate monitoring.In addition,the study found that the dip line of different working face usually maintains good accuracy,and is always better than the strike line.According to the research results,it is known that the surface subsidence is most obvious during the active period of subsidence in the coal mining subsidence process,and the monitoring of this phase should be strengthened.The mining geological conditions and the development of water system should be fully considered to reduce the adverse effects caused by surface subsidence.The results can provide a basis for the precaution of subsidence disasters and reclamation in high underground level coal mining areas.