Analysis of ecological water level recovery degree under coal mining subsidence dis-turbance in ecologically fragile area

LIU Shiliang; ZHANG Wenhui; WANG Ao; ZHENG Yusheng; MAO Deqiang

doi:10.12438/cst.2023-0971

Abstract：The variation degree of ecological water level in ecologically fragile areas is very important for ecological geological environ-ment protection.Ecological water level inevitably undergoes variation under coal seam mining.The current research focuses on the de-cline of ecological water level under mining induced groundwater leakage,with little consideration given to the ecological water level res-toration degree under non leakage of groundwater or disturbance of coal mining subsidence.For this reason,methods such as groundwater dynamics,groundwater level measurement,mathematical statistics,and comprehensive analysis are adopted,and an analytical method was proposed based on the idea of"distinguishing the leakage status of groundwater under coal seam mining→measuring the ecological wa-ter level changes in the coal mining face→establishing an ecological water level restoration degree well flow analysis model→predict-ing different ecological water level restoration times→comparing the analytical and measured values of different ecological water level restoration times"to study the degree of ecological water level restoration under the disturbance of coal mining subsidence in ecologically fragile areas.The results are as follows.①Based on"key strata layer location + thin plate theory + soil arch effect + descending fissure",a calculation method for the water-conducting fissure development height under overburden bedrock and soil structure is established,which overcomes the insufficient prediction accuracy caused by the existing empirical formula not considering the soil layer effect.Furthermore,combines the relationship between the thickness of the residual water-retaining layer and the aquifer seepage state,the aquifer seepage state is confirmed.②Under the disturbance of coal mining subsidence,the measured ecological water level shows a change law of"rapid decline first,slow recovery,and stabilization",but the ecological water level after coal mining can't completely recover to the premining state.③An analytical model of the recovery degree of ecological water level under the disturbance of coal mining subsidence is estab-lished.The analytical values of the recovery time of three different recovery degrees of ecological water level are estimated,and the time errors of both are less than 10%compared with the measured values.④The reasons for the incomplete recovery of postmining ecological water level to pre-mining state are discussed from the perspectives of surface topography,atmospheric rainfall recharge,recharge and drainage of phreatic aquifers,and underground water drainage in mining areas.