Process optimization and application of bolter miner for “three-soft” thick coal seam mining roadway

The overall strength of the surrounding rock of “three-soft” thick coal seam mining roadway is low, and the combination of rock structure generally changes greatly, resulting in obvious differences in the stability of hanging roof of driving face, and some areas with poor roof stability cannot directly adopt bolter miners and supporting construction technology, resulting in frequent stoppage of driving face and a decrease in the overall driving efficiency. In view of such problems, taking “three-soft” thick coal seam mining roadway of Shajihai Coal Mine as engineering background, and using comprehensive research methods such as on-site research, theoretical analysis and numerical simulation, it was clarified that roof leakage of driving face, bolter miner falling into the floor or mistracking, and rib spalling are the key constraints restricting the application of the bolter miner in “three-soft” thick coal seam roadway. Considering the influence of parameters such as the thickness of the hanging roof, the influence coefficient of disturbance, the strength of each rock layer of the roof and the integrity of each rock layer, the calculation formula of the limit span of hanging roof of driving face was established and derived. A stability grading method for surrounding rocks of roadway was formed dominated by the calculation of the limit span of hanging roof of driving face, and surrounding rocks of “three-soft” thick coal seam roadway is divided into 5 grades: extremely stable, stable, moderately stable, unstable and extremely unstable. Classification and optimization scheme of bolter miner equipment and construction process under different stability levels of surrounding rock is proposed, and the application countermeasures of bolter miner under difficult operating conditions are given from the aspects of cutting drum position adjustment, floor grounding treatment, and addition of roadway operation platform. The research results were applied in the roadway of Shajihai Coal Mine No.B1003W05 working face, and its classification optimization scheme can effectively ensure the normal operation of the bolter miner in “three-soft” thick coal seams, and the driving speed is increased by 1.0−1.8 times compared with fully-mechanized driving of boom-type roadheader.