Study On Reasonable Design Of BF2 Fault Coal Pillar In Qingdong Coal Mine

Faults are very common in the process of coal mining.When the fault drop is large,it is necessary to set up fault protection coal pillars to ensure safe mining.If the width of coal pillars is not reasonable,it will lose coal resources or cause water and sand inrush accidents.BF2 fault is the boundary normal fault of the third,fifth and seventh mining areas of Qingdong Coal Mine,with a drop of 70～170m.In the original design,100m waterproof coal（rock）pillars were set up,which caused huge loss of coal resources and technical rationality.Therefore,it is very important to study the reasonable design of coal pillar around BF2 fault.Based on the analysis of the latest edge technology and achievements of fault water-bearing and water-conducting exploration and the reasonable setting of large fault water-proof coal（rock）pillars at home and abroad,this paper aims to reduce the water-proof coal（rock）pillar on the hanging wall of BF2 fault of Qingdong Coal Mine.The hydrology and engineering geology of the mining area were studied.The fault hydrological supplementary drilling was designed and constructed on the ground,and the pumping test was taken to obtain the hydrological parameters.The rock samples were taken to carry out the analysis and test of lithologic characteristics and the experiment of hydraulic properties.The combination characteristics and water barrier characteristics of the overlying rock structure were obtained,and the evolution model of mining analysis on the hanging wall of the fault was constructed.FLAC^3D software was taken to simulate the evolution law of stress,displacement and plastic zone of coal seam roof and floor and fault zone during coal seam mining.Finally,the height of the collapse zone and the water-conducting fracture zone is obtained by using the theoretical formula method and the analogy method,and the safety retention size of the anti-waterproof coal（rock）column on the upper wall of BF2 fault was comprehensively determined.The completed work and the corresponding results are as follows:（1）According to the fine 3D seismic interpretation and the actual data of 13boreholes on both sides of the hanging wall and footwall of the fault,combined with the three main roadways of track,transportation and return air crossing the fault in the seventh mining area,three boreholes of 2021-BF2 water 1,2021-BF2 water 2 and2021-BF2 water 3 on the ground were designed and constructed.The water pumping（injection）test was carried out on the boreholes in the fault zone,and the unit water inflow was q=0.00010942～0.0623L/（s·m）,indicating that the water content of the fault was poor.In the underground,the transient electromagnetic method was used to carry out geophysical exploration of the fault fracture zone.Eleven water-rich exploration and verification boreholes were designed and constructed in the fault zone.The total amount of the project was 2158m,and the maximum water yield of the borehole was 1m³/h,and gradually attenuated.It is further verified that the BF2large fault is a water-free fault,which provides a scientific basis for the rational setting of fault coal（rock）pillars.（2）In view of the large fault drop and complex engineering geological conditions,it is easy to become a water-conducting channel.The ground directional grouting borehole is designed and constructed,and the high-pressure grouting filling transformation is carried out on the fault zone and the surrounding cracks.The cement slurry is injected into 13359.06t,which blocks the hydraulic connection between the fault and the aquifer,improves the engineering characteristics and water-blocking performance of the fault zone and its surrounding rock strata,and provides safety guarantee for the reasonable retention of fault coal and rock pillars.（3）Taking the fault zone and mining coal seam roof and floor rock samples,the rock mechanical property parameters test and water rational performance analysis test were carried out,and the rock uniaxial compressive strength,X-ray diffraction and other rock mechanical properties in the laboratory were obtained.It is concluded that the BF2 fault zone is mainly composed of rock layers with good water isolation performance.The roof and floor rocks of the coal seam are mainly argillaceous rock layers,with poor water conductivity and good water isolation performance.The rock mechanics parameters of the roof and floor of the coal seam with the same lithology are quite different.The rock in the fault zone is mainly composed of argillaceous body,the sand body content is low,and the clay mineral content is high.The content of Si O₂ in its chemical composition reaches 57.6%～60.6%,and the content of Al₂O₃reaches 24.2%～31.0%.The overlying rock type of the working face is weak to medium hard.（4）Based on the data of hydrological supplementary prospecting holes and drilling holes on both sides of the BF2 fault,a fault mining evolution analysis model was constructed.FLAC^3D numerical simulation software was used to study the variation of mining stress,displacement and plastic zone with different sizes of fault coal pillars.Result shows that under the condition that the width of the coal column on the BF2 fault is gradually reduced,the plastic zone of the roof of the working face is continuously developed,the roof settlement value is between 2.09cm and 3.39cm,the vertical stress value is increased from 25.78MPa to 29.02MPa,and the shear stress value is increasing.When the coal pillar is reduced to 29m.The plastic failure zone is not penetrated,and the mining area is relatively stable.Therefore,the upper panel of the BF2 fault is left with a width of 29m anti-water coal column.（5）The failure evolution law of overlying strata and waterproof coal（rock）pillar under the influence of fault mining are calculated by means of elastic-plastic zoning theory and specification of coal pillar.The results show that the theoretical height of the collapse zone is 16.0m,the theoretical height of the water-conducting fracture zone is 64.8m,the calculated height of the waterproof coal（rock）column is61.0m,and the maximum depth of the bottom plate rupture zone is 19.0m.The analogy method determined that the maximum collapse zone height of the working face near the BF2 fault was 22.0～28.9m,and the protective height of the coal column that needed to be left was 39.1～46.0m.According to the elastoplastic zoning method and theoretical formula of the coal column,it is calculated that a fault anti-water barrier coal（rock）column of not less than 28m should be left.Figure[49]table[25]reference[97]...