Stress evolution and rockburst control technology in coal seam composite zone of kilometer working face

The composite and bifurcation of coal seam are significant factors inducing rockburst and the stress distribution as well as the influence area is the key to the design reasonable prevention and control technologies. Taken a kilometer longwall mining in Zhangshuanglou Coal Mine as the engineering background,this paper studied the stress evolution laws and rockburst monitoring methods by numerical simulation and field microseismic system. The results show that the composite zone has an influence range of 100 m ahead the working face and the lagging area of 80 m. The peak stress is greater than that in the normal areas,the thicker the coal seam the greater the peak stress. When the working face is close to the composite zone,the stress gradient is the largest and the rockburst risk is the greatest. After entering,the stress increases slowly with the coal thickness,but the stress gradient is small,so the risk degree maintains stable as though the rockburst risk still high. After leaving the composite zone,the stress concentration is still high with obvious hysteresis. The strain energy index is proposed based on microseismic system which shows a strong consistency with the numerical simulation and the on-site underground pressure observing. Aiming to the large range of the bottom coal in the composite area,the super-deep inclined seam destress-water injection combined hole and parallel seam large-diameter-drilling are implemented in the composite area which realizes the full coverage stress relief of the coal,and takes a significant rockburst prevention effect to ensure the safety and efficient recovery of the working face.