Tubular roof bit design, and evaluation of roof drag-bits

The method of supporting excavated roof in coal mines by conventional roof bolting systems is challenged due to its shortcomings of the timeconsuming installation and the increased number of accidents attributable to the work under unsupported roofs. Though a few alternatives have been considered, the ultimate and most efficient bolting method has often been conceived as the one called a self-drilling roof bolt, or a Rapid Face Bolting System. The on-going Rapid Face Bolting project undertaken by the University of Wollongong includes a special drilling bit design, and the principal design considerations for this tubular roof bit are high efficiency and low cost. Through review of the physical properties of different cutting materials, considering the special needs of the project and establishing a series of special criteria for a tubular roof bit design, two kinds of tubular roof bolts are proposed to suit hard and soft rock formations, respectively.