Water-Inrush Mechanism And Prediction Of Fractured Floor Based On Coupling Of Seepage And Stress

The safety mining of the 13th coal seam in Baode coal mine on the Ordovician limestone confined aquifer was researched in this paper. The recharge, run off and discharge conditions of Tianqiao spring basin in our studying area, general hydrochemical characteristics and intensive runoff zones characteristics were firstly analyzed. The water yield property, karst water runoff condition evolution, water level variations and seepage field characteristics of Ordovician limestone in our studying area were detailed researched. The adopted methods were hydrochemical analysis and GSM numerical simulation combining with area water level data, drilling data and water pumping data. The fracture destruction compression-shear model of fractured floor rockmass was established. And the fractured floor rockmass' rupture and damage mechanism under seepage and stress coupling was discussed on the basis of Mohr-Coulomb fracturing criterion and effective stress principle. The fracture strength computing formulas of rockmass with a single fracture and fractured rockmass were obtained after the theoretical derivation. That layed theoretical foundations for the calculation of floor failure depth and damage zone height. The affecting factors of floor water-inrush were analyzed. The computing formulas of floor failure depth and damage zone height arised when theory solutions for fracture strength of fractured floor and the mode I stress intensity factor were referenced based on the "down three zone" theory. From the perspective of water-resisting layer'thickness and lithological association, the separating water ability of water-resisting layer was evaluated comprehensively and the sedimentary characteristics were researched. The computing formulas of water-resisting layer'ultimate water-inrush pressure were derived with the comprehensive consideration of working face width, water-resisting layer'thickness and lithological association on the basis of rock mass limiting equilibrium theory. The fractured floor water-inrush dynamic mechanism was presented, and it was thought that the water inrush from fractured floor was by the strengthening of seepage and stress coupling. The underground pressure propagation to the floor led to the ever-changing of stress state in the floor rock mass, and also the seepage pressure,which promoted cracks' extension and coalescence, even the whole water-resisting layer, the water inrush happened at last. The water inrush coefficient method and ultimate water-inrush pressure of water-resisting layer with L=200m were applied to predict the water inrush danger of 13# coal seam in Baode coal mine and divided the water inrush danger areas respectively. With the comparison it was found that Pz-M and Ps(0.1)-M matched well when L=50-70m.And Pz-M was the fit line of ultimate water-inrush pressure and thickness of water-resisting layer, Ps(o.i)-M was the relation line of security pressure and water-resisting layer thickness when Ts=0.1MPa/m. Pz-M and Ps(0.06)-M matched well when L=100-150m. While L increased a bit, Pz-M deviated from Ps-M gradually, and the increase of L decreased the effect of water-resisting layer's thickness on floor water inrush.