| In order to excavate hard rock more efficiently at faster rates, improve the working life of the cutting tool and reduce power requirements, the program described in this dissertation deals with means for enhancing the mechanical excavation of rock by effectively combining drag bit, with a high pressure waterjet and a wedge breaker based on both conventional and innovative concepts. The rock/waterjet/cutter theory behind this technology have been examined using a computer simulation of the stress distribution in the rock and combined with a mathematical modeling of the complete process in terms of drilling rate. Experiments has been carried out to validate the theory and were further extended to explore various applications of waterjet enhanced fragmentation in drilling and slotting. It was found that the achievements in this program can also be used for small hole drilling such as roof bolt hole drilling and blast hole drilling, as well as applied in the excavation of large holes such as tunnels and underground mining passages.; The first approach examined is referred to as Waterjet Assisted Mechanical Excavation of Rock, in which novel configurations of bits have been designed for use with high pressure waterjets directed to impact the cutting zone both so as to cool the cutters and to exploit cracks and remove the resulting debris. In particular, the study examined the use of Polycrystalline Diamond Compact (PDC) inserts. This technique has proved to be an economical tool in small hole drilling, a view enhanced by this program. The second approach is referred to as Offset Combined Cutting of Rock (OCCR) with Waterjets and Mechanical Tools, a technical innovation, in which the mechanical tool is used to create a favorable tensile stress field in the rock at a point, separate from the tool application, at which fracture is required. High pressure waterjets are then directed at this point, and are able to penetrate into the crack openings and induce rock failure. This technique has proved to effectively break rock with lower specific energy, and at lower jet pressures. Slot-and-Break excavation methods based on this principle have been applied to create an initial slot around the projected perimeter of a tunnel. |
