Roof stability of the mining face under the condition of water and sand inrush

For better roof control in the western coal mine,the convex structure model was built and verified by laboratory experiments to explain the mechanical mechanism of friction coefficient and roof stability of the mining face under the condition of water and sand inrush.The influence on the friction coefficient between rocks of surface convex structure,water,dry sand,wet sand,water-sand,etc were studied systematically.The results indicate that the convex-like structure will be formed at the interface between rocks due to the water and sand inrush,and sand will abrade convex structure,water will lower its shear strength,which all make the convex direction angle to converge to zero,and eventually make the friction coefficient be greatly reduced.It also explains why the rough surface friction coefficient is higher than the value of smooth surface,and why it’s easy to result in sliding instability and bench convergence instead of deformation instability in the face under the condition of water and sand inrush.In the position where rock starts to fracture,the contact is perfectly fit,so the activating friction coefficient is very big,and that is particularly important for the maintenance of roof stability.Specifically,to fill the mined-out area and strengthen the supporting measures can maintain the activating friction.At the same time,the more water in the water-sand,the lower friction coefficient is.Therefore,drainage is also critical in mining operation.