Evaluation of water inrush risk of seam floor based on lithology-structure

Water inrush risk prediction and evaluation of seam roof and floor are the foundation of water inrush disasters prevention in coal mines.According to the waterproof medium conditions of seam floor, the mechanical properties of coal-measure rock and the lithology, structure and thickness of seam floor were analyzed, the theory and methods of water inrush risk evaluation of seam floor were founded.It is shown that the waterproof medium conditions of seam floor depend on the lithlogy of aquifuge and the structure.Water isolating of seam floor becomes better with the increase of shale percentage content, but the ability of resisting water pressure was reduced.The aquifuge of seam floor changes from complete structure and block structure to cataclastic structure and loose structure with the increase of the fault development.The ability of resisting water pressure and water isolating of the seam floor decrease, and the water inrush risk increases.The ability of resisting water pressure of seam floor and the thickness of the aquifuge of seam floor are closely related.Statistical analysis showed a second power functional relationship between the limit water pressure (p) of seam floor and the thickness of aquifuge of seam floor (h).The lithology and structure characteristics of the aquifuge were considered.The classification of water inrush risk evaluation of seam floor was proposed.Whether water inrush occurs is judged according to the relationship between hydraulic pressure(P_w) and rock mass rupture pressure (P_c) and the relationship between hydraulic pressure(P_w) and the minimum principal stress (σ_hmin).