Roof stability for repeated mining workface passing through abandoned parallel gateway

According to calculating of the support strength when the repeated mining face passing through abandoned parallel gateway,a mechanical model for studying the principle of main roof fracture was established through spot investigation and analysis for fracture of roof of workface.Three factors such as the width of coal pillar between repeated mining face and abandoned parallel gateway,the distance between repeated mining face and main roof fracture line and the width of abandoned parallel roadways which may lead to the advanced fracture of main roof was put forward.Through the analysis of the three factors,the mechanical mechanism of advanced fracture of main roof was obtained.It shows that the coal pillars become destabilization when coal being extracted.The destabilization of the coal pillars leaves roof beam unsupported and increases the length of cantilever beam.When the length of cantilever beam is greater than or equal to cycle weighting interval,the cantilever beam breaks.Based on the Bieniawski formula,the critical width of coal pillar that becomes destabilization and the critical width of abandoned parallel gateway that main roof inevitably breaks in advance are calculated.The size of broken rock block of mechanical model of main roof weighting is adjusted on the basis of the mechanical model of main roof fracture.The adjustment is used to calculate the support strength of hydraulic support when repeated mining face passing through abandoned parallel gateway.It shows that the least support strength is 10 910.77 kN.On-the-spot observation results show that the support strength is 9 656 kN when repeated mining face passing through abandoned parallel gateway.