Evaluation And Prediction Of Water-richness Of Unconsolidated Confined Aquifer Andstudy On Setting Waterproof Coal Pillar When Mining Under Unconsolidated Aquifer

The Quaternary unconsolidated confined aquifer of North China-type coalfield is covered by coal measure strata.It is a hot spot in the study of prevention and control of roof water hazard,groundwater resources management and ecological environment protection in mining areas.This kind of aquifer is confined with unconsolidated sand and gravel and obvious interbedding of sand and mud,following by spatial distribution difference of water-richness.Therefore,it is necessary to accurately evaluate the water-richness of unconsolidated confined aquifer and scientifically and reasonably set up safe coal and rock pillars.This paper takes Huaibei coalfield as the research area.Firstly,on the basis of fully collecting and sorting out the geological and hydrogeological data of many coal mines in Huaibei coalfield,multiple factors affecting the water-richness of aquifer are selected for analysis.Then,the influence factors were selected to establish the multi-factor complex model of water-richness assessment on unconsolidated confined aquifer by combining AHP with CRITIC on account of game theory.Finally,the exploratory hole D9 and 7₁coal seams and its roof and floor sedimentary rock mass within 7₁21 working face of Qidong Coal Mine are selected as prototypes,with the help of two-dimensional discrete element software UDEC,this paper studies how to scientifically reserve waterproof coal and rock pillar in mining under unconsolidated confined aquifer.The specific research results are as follows:（1）The following six factors as the assessing indexes were selected including water-resisted coefficient（R）,groundwater lever coefficient（G）,aquifer thickness（S）,thickness of the thickest sand layer（M）,gradation coefficient（D）and interbedded sand and mud coefficient（P）to establish the multi-factor complex model of water-richness assessment on unconsolidated confined aquifer by combining AHP with CRITIC on account of game theory,which avoided the subjective or objective characteristic when weights were separately determined by AHP or CRITIC.（2）The evaluation results of the model were in accordance with‘Detailed Rules for Coal Mine Water Prevention and Control’,with the accuracy rate to 90.91%.Moreover,these selected factors could be obtained from the data of ordinary geological exploration boreholes,so there was no need to carry out too many field pumping tests and geophysical explorations.The model was applied to a specific engineering case affected by mining,and accurately assessed the temporal and spatial dynamic change of water-richness of unconsolidated confined aquifer.（3）Taking 7₁21 working face of Qidong Coal Mine as the research area,by“three under”specification experience formula,drilling results analysis and numerical simulation analysis,the development height of water flowing fractured zone in working face is determined comprehensively,and waterproof coal rock pillar is reserved scientifically and reasonably.This research results have a certain reference value for ensuring mine safety production.