Application Research On Strength Weakening Of Steeply Inclined Coal Seams Mining By Water Injection

Destabilization of hard roof of mined-out area is one of crucial problems that restrict safety mining in extremely steep and thick coal seams. Spatial space of mined-out area enlarges rapidly with increment of sectional height of the coal seam; In addition, large-scale hanging roof can be formed in the mining operation due to high rock strength and seldom fissures and cracks, which must bring hidden danger to safety mining in the stope. Water-injection measure for weakening rock masses has been put forward and taken as a scientific basis on roof stability in the mined-out area.Comprehensive analysis including theoretical analysis, laboratory experiment, numerical calculation and field monitoring was adopted. Mechanical model of strength weakening by water injection has been established with considering water-injection theory for the steeply inclined rock mass. According to testing on mechanical-AE parameter for the steeply inclined rock mass, failure strength, elastic modulus and characteristics of deformation were totally compared and analyzed. Several rock material groups with different homogenous degree and settings were used in the numerical simulation with RFPA software. The simulation result is consistent with the result in the mechanical testing. Additionally, the water injection of the steeply inclined rock mass has also been simulated and relevant data showed that stress around water injection hole decreased with increment of water injection amount. Besides, AE signal was obvious in the zone of water injection while almost inexistence in the zone of none water injection. Using micro-seismic monitoring system, big events decreased after water injection and the energy was uniform particularly, which showed that cracks developed obviously in the roof and the strength of roof decreased effectively.This research provides a scientific basis to weaken the roof strength of the steeply inclined rock mass, and it has a guiding significance for stability control of roof of mied-out area in the similar condition.