| With the gradual exhaustion of shallow coal resources,the mining of No.1 coal seam in the eastern Liuzhuang Coal Mine in Huainan coalfield is faced with the water-inrush risk of multi-layer Carboniferous karst aquifer and Ordovician karst aquifer underlying No.1 coal-floor.In this study,basic theories of structural geology,mine hydrogeology,groundwater dynamics,rock mechanics,underground mining,hydrogeochemistry,hierarchy-variable-weight and fluid-solid interaction are applied to solve the problem.Using the analysis of geological and hydrogeological conditions of the study area,calculation and analysis of multiple geological information correlation,data analysis of permeability test of fault zone rocks,numerical simulation and analysis by FLAC3D,numerical simulation and analysis by MODFLOW,the water-inrush risk of No.1 coal-floor in No.2 of the eastern mining area and the initial working face is studied,the dewatering quantity of karst aquifers is predicted,and the dewaterability of karst aquifers is analyzed.The results generally conform to the actual conditions of mine production.Main conclusions of this study are shown as follows:(1)Based on the analysis of geological and hydrogeological conditions of the study area,the main water-filled aquifers of No.1 coal-floor are determined.The direct water-filled aquifers of No.1 coal-floor are the 3rd and 4th layers of Carboniferous karst aquifers,and the indirect water-filled aquifers are the 11th and 12th layers of Carboniferous karst aquifers,and the Ordovician karst aquifer.The stress field type of Liuzhuang Coal Mine is between the geodynamic field and the quasi-hydrostatic stress field.(2)Based on mine hydrogeology and the concept of mine water-filled conditions,a concept of "collaboration-competition" is proposed,and a mathematical assessment method for coal-floor water-inrush risk integrating the hierarchy-variable-weight model(HVWM)with collaboration-competition concept is established.The model is applied to the eastern mining area of Liuzhuang Coal Mine.By comparing the evaluation results of constant weight,variable weight,and hierarchical-variable-weight models,it can be concluded that the differences of the three methods are determined by their respective characteristics.The index weight of the constant weight model is fixed in the whole study area.The variable weight model "punishes" the relatively low values that are not conducive to water-inrush,and "stimulates"the relatively high values that are conducive to water-inrush,and it neither motivates nor punishes the intermediate values.Thus,the method increases the overall risk level comparing with the constant model.While HVWM analyzes the relationship between the main controlling factors from three aspects by building upper main controlling factors,and readjusts the weights of the upper main control factors,making the results more reasonable.Under the condition of multiple aquifers underlying coal-floor,the differences of water-inrush risk level in a single aquifer and the differences in overall risk level between different aquifers should be considered,and the water-inrush risk between different aquifers cannot be isolated.(3)By analyzing the data of triaxial compressive seepage test and in-situ permeability test of the main fault zone rocks in Liuzhuang Coal Mine,the characteristics of stress-strain-permeability relationship of different lithologies are obtained.The stress-strain-permeability relationship curves of different lithologies show different characteristics,but a general law of permeability changes can be concluded:at the initial stage,permeability changes are not obvious in the rocks with less initial fissures,while the rocks with relatively developed initial fissures are compacted.At the elastic stage,with the continuous expansion and connection of newly generated fissures,the permeability of rock increases continuously.According to the characters of lithologies,the maximum permeability appears before or after the peak stress.With the increase of stress,the permeability may continue to increase or decrease,or it may not change anymore,depending on the evolution of fissures in the rock.The in-situ permeability test results show that the changes of rock permeability appear certain differences with different water pressures,but the overall permeability shows an increasing trend with the increase of water pressure.With the variation of water pressure and stress disturbance,the permeability of rocks in the fault zones will change,and the fissures in the rock mass will expand and seepage channels will be formed.(4)FLAC3D is applied to construct a numerical model of pseudo-inclined long-arm working face for excavation,and the mining-induced failure characteristics and seepage evolution process of surrounding rocks in six excavation steps are analyzed.The tensile failure of weak materials is limited with confining pressure,such as fault zones,and shear failure will be the main failure form.The possibility of lagging water-inrush in fault zones is greater than the possibility of instantaneous water-inrush.The possibility of lagging water-inrush is higher in DF2 fault zone,among which the possibility of water-inrush is higher in the fault zone near the upper-laneway,and the possibility of water-inrush in DF6 fault zone is lower than that in the DF2 fault zone.With the disturbance of the adjacent working faces,the possibility of water-inrush near goafs of the lower-laneway increases gradually.With the increase of the pressure relief range in the No.120101 working face,the pressure relief range of upper two-zones will increase and extend upward,if pondings on goafs and/or partial strong water abundance aquifers exist above coal-roof,the risk level of mining will be relatively high.(5)By analyzing the distributions,boundary conditions,movement,development,and chemical characteristics of karst aquifers in the study area,it can be concluded that the hydraulic connection between the direct and indirect water-filling aquifers is weak with the absence of passages,and the hydraulic connections between the lower part of Carboniferous karst aquifers and Ordovician karst aquifer is closely related.Certain range of the karst aquifers develops in a reducing environment.The karst aquifers in the study area have poor runoff conditions,and are in a relatively enclosed groundwater environment.The karst fissures are relatively developed around fault zones,and the shallow karst fissures are relatively developed.The general water abundance of Carboniferous karst aquifers and the Ordovician karst aquifer is poor and extremely inhomogeneous,and the permeability and connectivity of the aquifers are poor.(6)Based on the analysis of the characteristics of karst water-bearing rock groups,a hydrogeological conceptual model of karst aquifers' system is constructed,and then MODFLOW is applied to build a numerical model of three-layer structure of karst water movement.Numerical simulation of dewatering quantity prediction of karst aquifers shows that,theoretically,it is difficult to lower the water level of karst aquifers to safety water level only by setting a large number of pumping wells on the ground,and it is necessary to combine ground and underground methods to lower the water-inrush risk.(7)A tentative combination method of karst water hazard controlling is proposed,namely "ground interception,grouting reinforcement,underground drainage".Karst fissures of the hidden outcrop can be grouted on the ground to block water supply passages of karst aquifers,and then the No.1 coal-floor especially on the scope of concealed structures can also be reinforced by grouting underground,accompanying with geophysical exploration and drainage underground. |
PDF Full Text Request