Experimental study on the influence of width-height ratio on coal pillar type rock burst

The deep coal mining in China is becoming more and more complicated. Under the influence of mining, structure or hard roof and floor, the section coal pillar is easy to induce coal pillar type rock burst. The prevention and control of coal pillar type rock burst has become a difficult problem in coal mine safety and efficient mining. It is of positive significance to study the mechanical properties and impact failure characteristics of section coal pillars under different width-height ratio for the prevention and control of coal pillar type rock burst. Uniaxial compression experiments were carried out on the “rock-coal-rock”combination of coal samples with different width-height ratio. The influence of width-height ratio on the impact failure of coal pillars was studied by analyzing the impact tendency, dynamic failure characteristics, fractal dimension and acoustic emission characteristic parameters of the combination. The results show that: ① The width-height ratio of coal pillar has a significant effect on the impact tendency of the combination. When the width-height ratio is not less than 2∶1, the impact energy index KE is 1.82−2.65, and the impact tendency has no obvious change. When is less than 2∶1, the impact tendency increases first and then decreases. When is 1∶1, KE is the largest, reaching 15.43. ② With the decrease of width-height ratio, the failure characteristics of the composite body are as follows: tension-compression failure-compression-shear failure-tension-shear failure. When the width-height ratio of the coal pillar is 5∶1−3∶1, the damage of the combination is relatively slow. When the width-height ratio is 2∶1, the flake coal chips begin to pop out, and the degree of impact damage is low. When the width-height ratio is 1∶1 and 0.75∶1, it has obvious impact failure characteristics. When the width-height ratio is 0.5∶1, the overall stability of the combination decreases, and the severity of the coal pillar failure of the 0.75∶1 sample combination decreases. ③ The energy release rate of post-peak acoustic emission is similar to that of fractal dimension D, which increases first and then decreases with the decrease of width-height ratio. When the width-height ratio is not less than 2∶1, the energy release time is longer during the failure process of the combination, and the coal pillar failure is gentle. When the width-height ratio is 1∶1, the energy release rate and D value increase significantly. Compared with the energy release rate of the combination with a width-height ratio of not less than 2∶1, the energy release rate increases by about 4 times, and the D value increases by 0.18−0.23. The impact damage of coal pillar is the most severe. The energy release rate and D value of the 0.75∶1 combination were reduced by about 10% and 0.01, respectively, and the damage severity was similar to that of the 1∶1 combination. When the width-height ratio is reduced to 0.5∶1, the reduction of the relevant parameters is about 6 times that of the 0.75∶1 combination, and the degree of damage is relatively small.The results show that the width-height ratio has a significant effect on the impact failure of coal pillars. On the whole, the intensity of impact failure of coal pillars increases first and then decreases gradually with the decrease of width-height ratio (5∶1−0.5∶1). When the width-height ratio of coal pillar is greater than 3∶1, the rock burst risk is relatively small. When the width-height ratio of coal pillar is 1∶1 and 0.75∶1, the rock burst risk is larger, followed by 0.5∶1.