Prediction Theory And Method Of Water Inflow From Roof Thick Layered Aquifer Of Coal Mining Face

In recent years,with large-scale exploitation of coal in the west of China,problems of water inrush from roof aquifer has become more and more serious,and threatens mine's safety.There are still many shortcomings in the research on problems related to water inrush from roof aquifer,mainly as follows:Such as poor research on vertical hydrogeological characteristics of thick multilayered confined aquifers,and insufficient research on height of water flowing fractured zone,unclear about principle of water inrush from aquifers in the roof,and there are also many problems with hydrogeological models and calculation methods of water inflow,etc.Mines in Binchang mining area of Huanglong coalfield are typical mines with heterogeneous and thick sandstone aquifer on the roof of coal seam.Taking the first mining area of Gaojiabu minefield as an example,the thickness of coal is thick?between 3.00¹8.13 m,with an average of10.75 m?,the thickness of Luohe formation is huge?between 318.00⁵09.93 m,with an average of 400.35 m?,and it's strong water-rich?the maximum q is 2.248 L/?s·m??,the distance between the aquifer and the coal seam is small?between 31.81¹60.30 m,with an average of 84.02 m?,depth of coal seam is large?about 1 km?,groundwater pressure of aquifer measured underground is big?groundwater pressure of Luohe formation can up to 7.4 MPa?,and water inflow in the working face and the mine continues to be huge?The maximum water inflow of working face can reach 1200 m³/h,and now the mine water inflow has been more than 3000 m³/h?.For now,water inflow has become the primary problem limiting coal production and threatening mine's safety.Therefore,research on issues related to water inrush from roof aquifer has important theoretical significance,social significance and economic significance.Taking Gaojiabu minefield as an example,this paper systematically and thoroughly studied the difference of vertical hydrogeological characteristics of sandstone aquifer in Luohe formation,the mechanism of water inrush from roof aquifer to working face and the prediction theory and method of water inflow from roof aquifer to working face.In this paper,Gaojiabu mine field is taken as a typical research area.Through the comparative analysis of hydrogeological characteristics and hydraulic connection between aquifers,the vertical hydrogeological characteristics of Luohe aquifer are finely studied.Methods including injection water leakage measuring in upward slant hole,underground-gound joint microseismic monitoring and numerical simulation with UDEC software are used to determing height of water flowing fracture zone of the typical working face.It studied the law of height of water flowing fractured zone caused by fully-mechanized caving mining in the research area.It use the basic theory and method of groundwater dynamics and mine hydrogeology to study the law of groundwater movement from thick multilayered confined aquifers to mining face,theory and method forecasting water inflow from roof aquifer to working face.It also do Engineering application.This paper have achieved the following innovations.?1?For the first time,Luohe formation in the research area is divided into the upper,the middle and the lower aquifer,and its vertical hydrogeological characteristics are fine studied.The research results show that:The lithologies upper and lower aquifers are mainly sand-shale interbeds with an average thickness of 77.52 m and 72.57 m,respectively,and the middle aquifer is dominated by fine,medium and coarse-grained sandstones with an average thickness of 236.95 m;the average porosity of the upper aquifer is 10.82%¹6.69%,the middle is 19.21%²3.63%,and the lower is12.45%¹8.18%;the upper groundwater level is+925.75⁺925.99 m,the middle is+928.26 m,and the lower is+926.36⁺926.52 m;the upper temperature of groundwater is 28²9°C,the lower is 35³7°C,and the middle is between 29³5°C;the upper K=1.113 3¹.487 4 m/d,the lower K=0.029 1⁰.029 6 m/d,and the middle K=1.339 7³.741 9 m/d;the upper q=0.516 4⁰.774 1 L/?s·m?,the water-rich is medium,the lower q=0.010 7⁰.012 8 L/?s·m?,and the water-rich is weak,the middle q=1.4895 L/?s·m?,and the water-rich is strong;the groundwater salinity of the upper is 1.033 g/L,the lower is 3.824 g/L,and the middle is about 1.130¹.254 g/L.?2?For the first time,formula and application conditions for predicting height of water flowing fractured zone(H_li)under the influence of the width?B?and the mining height?H?of working face caused by fully-mechanized caving mining in Huanglong coalfield are obtained,which enriches the predicting method of water flowing fractured zone caused by fully-mechanized caving mining.The formula is:H_li=0.815B+10.577H-60.486Applicable conditions:under the medium-hard roof stratum,using the fully-mechanized caving mining,the width of mining face is 90²40 m and the height of mining is 4¹3 m.The height of water flowing fractured zone is affected by the width and the mining height of working face.When the width is fixed,the ratio between height of water flowing fractured zone and height of mining decreases while mining height increase,which tends to the[11.00,14.30];when the mining height is fixed,the ratio increase while the working face width increase.?3?Question of groundwater flow from confined aquifer to underground well is studied.Based on the analytical formulas of groundwater flow from confined aquifer to groundwell under condition of pumping test,this paper has analyzed and compared the similarities and differences between the pumping test of groundwell and dewatering of underground well,and obtained analytical formulas of dewatering of underground well under condition in full penetrating underground well and in partially penetrating underground well.?4?Based on the research results of groundwater flow in dewatering underground well,this paper has proposed the hydrogeological conceptual model of“underground dewatering well”,and given the calculation method of“underground dewatering well”for predicting water inflow from roof aquifer to working face,which enriches prediction method of water inflow.The method asume the aquifer destroyed by the water flowing fractured zone as“a very big underground dewatering well”,and the radius of the“big well”increases while the mining of the working face continues.Meanwhile,the method consider the amount of water released and dynamic recharged of the aquifer,and the vertical recharge of the upper aquifer.By predicting the amount of water inflow to the working face?Gaojiabu mine 101 working face?and comparing with the actual water inflow,it is verified that the"underground dewatering well"can predicts the dynamic water inflow during the mining process.