To verify the feasibility and efficiency of rotary-percussive drilling assisted by waterjets in very hard rocks, experiments on the performance of Polycrystalline Diamond Compact (PDC) cutters resisting different combined loads of static thrust, impact, cutting and waterjets on Missouri red granite and Halston limestone were investigated. The experiments were conducted by means of a drop hammer and linear cutting-impact table. The effects of static thrust (WOB), impact energy, impact spacing and waterjets on the rate of penetration in hard rocks are described and the results are analyzed by measuring the depth of the craters or cuts penetrated by PDC cutters. Results from the study confirmed that the combined mode of cutting-impact is very effective in very hard rocks.
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