Dust suppression mechanism and application of downward sealed-hole water injection in an open-pit coal mine

During coal excavation using a single-bucket excavator in an open-pit coal mine, coal dust is generated in an open working environment and is readily dispersed over a wide area under the influence of airflow. Consequently, conventional spray-based dust suppression methods are generally unable to effectively control such dispersed dust. To address this problem, a novel downward sealed-hole coal-seam water injection technology was proposed for open-pit coal mines. The mechanism of downward sealed-hole coal-seam water injection was investigated, and the results indicated that the coal mass was wetted progressively from top to bottom through the synergistic effects of pressure-seepage flow and the natural seepage of gravity water. Field tests conducted at the open-pit coal mine demonstrated that, when the water injection pressure was lower than 11 MPa, the sealing water pressure should be maintained at approximately 6 MPa. When the water injection pressure exceeded 11 MPa, the sealing water pressure should be no lower than 8 MPa. In addition, the water injection flow rate for a single downward borehole should be controlled within the range of 20 to 24 L/min. Following downward sealed-hole water injection into the coal mass, the dust suppression efficiencies measured at locations 0.5 m from the left and right sides outside the operator cab during coal excavation by the single-bucket excavator reached 77.4% and 76.0%, respectively, demonstrating that the proposed technology achieved a satisfactory dust suppression performance.