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Based on the effect of depressurization, rapid depressurization property of dual-power drilling was investigated. The realizing condition of dual-power drilling and the principal of helical coal breaking were analyzed theoretically. Adopting the FLAC3D software, the model was established to study the rules of stress revolution around the relaxed slot. Besides, the industrial experiment was conducted. It indicates that the advanced free surface can eliminate the confining pressure and lower the resistance, increasing the drilling rate significantly. The relaxed slot boost the coal mass rheology occur, making the concentration stress move deeper, gas potential energy released, the coal strength enhanced and thus the fatality of outburst removed. Industrial experiment shows that after adopting this measure, the perturbation range enlarges forty times and the depressurization radius four times. The efficiency of gas drainage improves substantially, the fatality of outburst in control region is removed and tunneling progress raises two times. [ABSTRACT FROM AUTHOR]

Different models were built to simulate the crack propagation modes with different lateral pressure coefficient of hydraulic slotting area. The results show that if lateral pressure coefficient λ < 1, crack propagates along horizontal direction. When λ = 1, crack around the slotted borehole distributes uniformly. Except the above situations, the crack mainly locates in vertical direction. In addition, the number of cracks around the borehole increases with λ linearly. A similar law can be found with different λ by recording the evolution of kinetic energy. Besides, peak value of kinetic energy increase with λ. The acoustic emission (AE) shows different characteristics with different λ. While λ is small, AE events distribute discretely, when λ = 1, AE events distribute uniformly during the whole process, if λ > 1, number of AE events increase sharply first and then decrease. [ABSTRACT FROM AUTHOR]