Rock fragmentation by cutting, ripping and impacts : some theoretical and experimental studies

Sammanfattning: Models of different forms of rock fragmentation are presented, having mainly two purposes; to increase the understanding for the fragmentation processes, and to form a base for quantitative predictions. The results of some full scale rock cutting tests are also presented. The thesis consists of five separate papers. Paper A deals with models for capacity predictions, such as boreability tests, for full-face boring. Hardness and strength parameters have a large influence on mechanical boring, and these are two essential parameters that should be included in boreability tests. Paper B presents the results of two full scale cutting tests. Comparisons between button cutters and steel discs, and between single and double discs are made. Single discs give the highest penetration, multiple discs or rows of buttons give a smoother rum and lower torque. Paper C presents a model for side chipping between disc cutters, based on an assumption of tensile failure in the rock. The model is tested in full scale, in the laboratory. Paper D deals with rock failure models for picks on roadheaders. A laboratory test in full scale showed that models which assume a specified geometry of the chips are questionable. The process should instead be treated as a series of independent breaking events. A model based on consumed energy in cutting is also presented. Paper E deals with impact breaking of rock with hydraulic hammers, applied on secondary breaking of oversize boulders. A method to predict the breakability of rocks is presented. The test method is compared with two sets of measured field data. The agreement was acceptable, but the model should be developed further, to include the effect of varied impact energy. Models of rock behavior usually try to explain the underlying phenomena. This may be very difficult in a nonhomogeneous material like rock. In those cases, it is better just to measure and map the visible effects, and use the results to improve existing techniques.