Preharvest Water Safety Evaluation Of W3₂33 Working Face Of Qianyingzi Coal Mine

The first mining face W3₂33 in the west third mining area of Qianyingzi Coal Mine is located under the fourth aquifer of the new loose layer（referred to as the"fourth aquifer"）.The original design adopts stratified mining,leaving waterproof coal and rock pillars,and the resource loss is serious.In recent years,with the progress of science and technology,the identification of the mining grade of the"fourth aquifer"water body and the determination of the type of overburden rock,it is ready to reduce the protective coal pillar and leave the sand-proof coal and rock pillar mining.Therefore,whether it can achieve safe,green and efficient recovery of coal resources has become an urgent problem to be solved.Therefore,it is necessary to carry out pre-mining water prevention and control safety evaluation of W3₂33working face in Qianyingzi Coal Mine.Based on the background of retaining sand-proof coal pillars in W3₂33 working face of Qianyingzi Coal Mine,this paper analyzes the overlying rock structure and water-richness of W3₂33 working face of Qianyingzi Coal Mine on the basis of consulting the cutting-edge technologies such as mining under water body,movement and evolution law of overburden failure,height research of’two zones’,water disaster research of roof and floor and safety evaluation at home and abroad.The strength of water-richness,the design and implementation of underground transient electromagnetic and channel wave geophysical prospecting,the distribution range of roof water-richness and structural anomaly area,the design and construction of underground upward drilling for abnormal area.The rock samples were taken,the mechanical properties and hydraulic tests were carried out in the laboratory,the mechanical parameters such as compressive strength and elastic modulus were obtained,and the analysis model of mining failure characteristics was constructed.FLAC3D software was used to simulate the failure characteristics of overlying strata caving zone and water flowing fractured zone after mining.Combined with the calculation of’three under’mining specification and engineering analogy,the height of coal and rock pillar was calculated,the critical hydraulic slope and seepage failure were evaluated,the water inflow was predicted,and the drainage system was designed.The main research contents and results are as follows:（1）Qianyingzi coal mine W3₂33 working face machine lane length 3064 m,wind lane length 3185m,open-off cut design width 272m,working face design mining upper limit elevation-268.66 m,working face overlying bedrock surface elevation-195.86 m～-224.66 m,the average coal thickness 3.47m,the average dip angle of 15°,using comprehensive mechanized coal mining,all caving roof management.（2）The thickness of the fourth aquifer is 2.4m～13.85m,with an average of9.58m.According to the results of the 6-hole pumping test of the surrounding water,the unit water inflow q=0.0004921L/（s·m）～0.0033L/（s·m）,the permeability coefficient K=0.0004345m/d～0.04557m/d,the water-richness is weak,and the mining grade of the water body is classified as Class II according to the’three under’mining specification.（3）Using transient electromagnetic and in-seam wave to explore,it is found that there are 7 low-resistance anomaly areas and 8 hidden structures.No collapse column with a diameter greater than 20 m and large hidden structures are found in the working face.Through the construction of underground upward drilling,it is verified that the water-richness of 7 low-resistance abnormal areas is weak,and the’four-bearing’in the working face is not developed,the water-richness and water conductivity are weak,the three-partition is stable,and the overlying rock structure and K3 sandstone are weak.（4）The rock samples were taken in the laboratory for mechanical parameter test,XRD,XRF,nuclear magnetic resonance analysis test,and the uniaxial compressive strength,microscopic composition content and porosity of overburden were obtained.The uniaxial compressive strength is 11 MPa～44 MPa,and the overburden type is weak to medium hard.The relative content of clay minerals in overburden rock is high,and the water insulation performance is good.The pores are small and the pore structure is simple,the water conductivity is poor,and the water insulation performance is good.（5）The analysis model of mining failure characteristics is constructed.FLAC3D numerical simulation,theoretical calculation of relevant specifications and engineering analogy of adjacent working face are used to predict the height of water-conducting fracture zone is 43.45 m,45.60 m and 45.40 m,respectively.The height of caving zone is 14.23 m,12.78 m and 13.32 m,respectively.The height of sand-proof coal pillar is predicted to be 26.23 m,24.78 m and 25.32 m,which is less than the actual height of coal and rock pillar of 44 m.During the mining process of working face,the caving zone of overlying strata of roof will not affect the’four-containing’,which is in line with the condition of retaining sand-proof coal and rock pillar.Floor failure will not affect K3 sandstone,and the risk of water inrush from roof and floor of W3₂33 working face is low.（6）The critical hydraulic gradient and anti-permeability damage evaluation were carried out.The hydraulic gradient of’four aquifers’after mining was 0.0519～0.5796,which was less than the critical hydraulic gradient of"four aquifers"1.66,that is,J<Jcr.According to the condition of sand inrush,there will be no water and sand inrush,and there is no danger of water and sand inrush in the working face.（7）The water inflow is predicted,and the drainage system with drainage capacity not less than 110m³/h is designed.（8）The safety control technical measures for rapid and uniform mining and propulsion speed of about 5m/d are formulated to prevent and control the unbalanced damage of roof.（9）After the mining of the working face,two"two zones"height exploration holes were designed and constructed.The measured height of the caving zone after mining was 12.13 m,and the height of the water-conducting fracture zone was 40.19m,which were less than the predicted value and the actual distance between the coal and rock pillars.In summary,in view of the water disaster safety problem of W3₂33 working face,this paper constructs a technical system for evaluating the safety of pre-mining water prevention and control of working face,including hydrogeological analysis,geophysical exploration drilling verification,rock mechanical property test,numerical simulation and theoretical calculation of’two zones’height,critical hydraulic slope and anti-permeability failure evaluation,and’two zones’exploration hole verification research results.It is proved that W3₂33 working face has the conditions for setting up sand-proof coal pillars under the premise of good prediction and early warning.When the paper is completed,the working face has been mined295 m,and no water and sand inrush accidents have occurred.Figure[48]table[28]reference[84]...