On the Mechanism of Stress Superposition Inducing Outburst Under the Influence of Blind Fault Instability

The mechanism for coal and gas outbursts in normal blind fault areas is not yet clear. Coal and gas outbursts induced by normal blind faults exposed at the 22,703 working face in the Yanjiao Coal Mine were taken as examples to carry out numerical simulation, detection and inversion through radar computed tomography (CT) transmission. In combination with ground pressure monitoring data before/after outbursts, the mechanism driving outbursts induced by superposition of multiple stresses and subjected to the influence of blind faults was primarily investigated in the present study. The results indicated that due to a cutting action applied by a blind fault on rock masses, the intersection of the fault plane and coal seam always remains in a stress concentration state as the working face advances. In addition to the impact of mining-induced abutment pressure, the intersection of the fault plane and coal seam is also under the actions of tectonic stress. Once the 22,703 working face arrives at a position 15 m away from the fault plane, coal masses between the working face and the fault plane are entirely damaged due to joint actions of abutment pressure and tectonic stress. In this case, the coal mass loses its carrying capacity entirely; the overlying strata of the working face settle sharply, and the strata behaviour of the working face becomes intense. Consequently, coal and gas outbursts are induced. In addition, according to ground pressure data before/after an outburst event at the face, a significant rise in local ground pressure monitoring data suggests coal rock instability. Prior to such an outburst, the operating resistance of the hydraulic support in a local region may increase by 300% compared with its normal value, which is an early warning index for a potential area of outburst. Therefore, not only do regions where the ground pressure rises abnormally need to be further explored but also the gas stress of the coal mass should be synchronously checked. In this way, prevention and control measures can be made in advance.