Monitoring and control airblast overpressures in an open pit coal mine

Abstract

Besides ground vibrations, air transmitted vibrations or airblast overpressures (AOp), are also generated during blasting operations. Mae Moh coal mine, Thailand, has been concerned about both ground and air vibrations because the residents nearby are located less than 2 km to the southeast of the mine. Most previous studies mainly focused on the air blast prediction by using from basic generalized equations to the sophisticated Artificial Intelligence (AI) techniques. In addition, many controllable and uncontrollable parameters that affect AOp were extensively studies. Blasting operation unit at the mine uses a sequential blasting machine to detonate electrical detonators with a variety of delay time between rows and blasting directions. The wavefront reinforcement model was selected to test its theory that the levels of AOp will increase at the locations where wavefronts are reinforced and, at the same time, to recommend an appropriate delay time between rows and blasting directions that may reduce AOp. The wavefront reinforcement model accounts for input burden, spacing, and sequential delay time from blastholes to generate air wavefronts transmitted out in all directions. The overall 54 blasts were conducted and recorded AOp in dB(L) unit to test the model. Only 37 blasts that had one seismograph placed at the wavefront reinforcement area and another one placed at the non-reinforcement area could be compared. The results indicated that AOp levels were higher in areas of wavefront reinforcement compared to non-reinforcement in 29 (78.4%) of all valid blasts. Most air wavefront reinforcement occurred at in front and to the back of the blasting direction. The blasting patterns of the mine were studies and indicated that the delay time between rows or circuits should be nearly 200 ms to minimize the wavefront reinforcement areas. Graphs of cube root scaled distance were provided to illustrate the effect of blast direction on the increasing of AOp.