Model of mining-induced fracture stress-seepage coupling in coal seam over-burden and prediction of mine inflow

The prediction of mine inflow is an important basis for the coal mine safe production and waterproofingdrainage system design. The previous prediction methods did not consider the change of the overlying rock seepage characteristics caused by mining and the prediction results had large errors compared with the actual measurement.Taking the working face No. 1307 of Zhaoxian Coal Mine in Shaanxi Province as the research area,the authors modify the fracture stress-seepage coupling calculation model and propose a modified three-dimensional mining-induced fracture stress-seepage network calculation model on the basis of the seepage characteristics of the rough fracture surface of overburden caused by mining. Based on the development characteristics of water-conducting fractured zone and monitoring data of mine pressure,the orthogonal experimental model with different pitch and gap width combinations is designed. Using the modified three-dimensional mining-induced fracture stress-seepage network calculation model,the dynamic change pattern of mining permeability is discussed and the mine inflow is predicted according to the development trend of the water-conducting fractured zone. The results indicate that the stress field and permeability on the overlying strata changes due to the influence of mining,and the variation range of the seepage field is larger than the variation range of the stress field. The change of permeability is distinguished in different directions,and the influence range of the permeability coefficient in the horizontal direction is small and the amount of change is large. The range of influence in the vertical direction is large,but the amount of change is small. Comparing the predicted water inflow with the measured water inflow,the test model of stratification spacing is l1= 10 m,l2= 30 m,l3= 150 m and gap widthcombination is b1 = 0. 05 m,b2= 0. 01 m,b3= 0. 005 m,which is more accordance with the actual project situation of the research area. Finally,on the basis of the combination form of model distance and gap width,using the discrete element software fracture seepage model,the reliability of the fracture stress-seepage coupling calculation model is discussed. The simulation results are basically consistent with the fracture stress-seepage coupling model.