Theoretical And Experimental Research On The Reasonable Width Design Of Water Barrier Pillars For Mining Around Reservoir In Shallow Coal Seam

The research on the reasonable width design of water barrier pillars for mining around reservoir is one of the key issues to ensure the safery and green mining in coal mine,and the theoretical and experimental research on the reasonable widh design of water barrier pillars have important theoretical and practical value.The paper bases on the No.4-2 coal seam in Zhangjiamao coal mine,which is around the Changjiagou reservoir in Shenmu County,Shaanxi Province.This paper adopts theoretical analysis,physical similarity material test,FLAC3D numerical calculation and field practice to conduct research work.The paper gives the simiplifid model of mining around the reservoir.Base on the coupling relationship between mine pressure,water pressure and coal scam,it is proposed that the water barrier pillars for mining around reservoir along the width direction can be divided into the mine pressure influence section,the effective water barrier section and the water level influence section,and gives the definitions and formulas of water barrier pillars for mining around reservoir.The main factors that influence the width of the water harrier pillars includes slope,height,water level,height of fracture zone in overburden,strata movement angle and so on,According to the above factors the paper gives a comprehehensive method to design the widh of water barrier pillars,and gives the formulas of water barrier pillars.Finished the physical and mechanical properties of No.4-2 coal,and based on the acoustic emission test of uniaxial compression the paper gives the law of failure uniaxial compression and acoustic emission.Though the physical similarity material test analyzed the failure characteristics of overburden and reservoir slope,stress and displacement.It is shows that when the reservoir is full of water,the water barrier pillars shouldn’t less than 163m which can make sure the reservoir slope not affected by the mining;with the advance of the working face,the overburden constantly falling and gradually developed to the surface which can form a "subsidence basin",and when the scope of "subsidence basin" extend to the reservoir slope,there is a downward fissure in front of working face and the reservoir slope will overturning to the goaf;when the working face pushed to 221m and the water barrier pillars is 70m,there will be a sudden slippage between the different lithology levels,and the reservoir slope will slip.Based on the basic theory of seepage and deformation calculation,the paper gives the water-rock coupling control equation for mining around reservoir.In order to study the width of the water barrier pillars,the paper used water-rock coupling FLAC/L software to build a numerical model which has the same working conditions with the physical similarity material test.The criterion for the width of the water barrier pillars has be given that based on the water-rock coupling FLAC3D calculation results at reservoir slope and pore water pressure key points.The displacement curve of numerical simulation and physical similarity material test at the reservoir slope has the same tend.The width of the water barrier pillars is 99m which calculated by FLACID.Based on the water-rock coupling FLACii numerical analysis method,the paper studied the effect of mining on the stability of reservoir slope under different water level,analyzed the influence degree of water level to the width of the water barrier pillars.The results show that it has little influence on coal mining and the width of the water barrier pillars when the coal seam thickness and buried deepth are constant,the reservoir water level below the floor of coal seam and the coal seam located above the infiltration line and in the unsaturated zone;the width of water barrier pillars should be increased when the reservoir water level located in the middle of the coal seam;the width of water barrier pillars should be increased with the rise of the water level when the reservoir water level located above the roof of the coal seam;the width of water barrier pillars should be increased with the depth of the coal seam when the reservoir water level and thickness of the coal seam are unchanged.According to the results of theoretical analysis,physical similarity material test and FLAC3D numerical calculation,base on the different deformations the paper divided failure mode into five main modes:collapse,avalanche,landslide,scattered and dumping for the first time.And according to the different direction of slope deformation,each main model includes two sub patterns.The method to design the width of water barrier pillars is put forward that mining around reservoir in the shallow coal seam.By drilling,geophysical prospecting,sampling test,pumping test and hydrogeology charting to explore the hydrogeology conditions of Changjiagou reservoir,and on the basis of this,the paper gives four kinds of possible water hazards in No.4-2 coal seam mining around reservoir.According to the method of the width design of water barrier pillars in this paper,the width of water barrier pillars is 99m and the working face layout of the No.4-2 coal seam has been completed.The engineering practice proved that the width of water barrier pillars is reasonable.