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This study experimentally validated the reliability of the lab-scale rock drill apparatus and investigated the effect of bit design factors on the performance of drilling. To test drilling efficiency of a drill bit, a testing system was designed and manufactured. Using the testing system, the drilling rates and specific energy of a conventional drill bit and newly proposed drill bit with different button arrangement were compared. The newly proposed model was tested to be superior in drilling performance than that of the conventional model. The testing system developed in this study could be used to predict and test the performance of newly developed drill bit models. Also, the system has to be improved further for measuring more accurate and quantitative data for future drill bit developments.

The percussion rate and spacing of the button of drill bit are very important in maximizing the drilling efficiency. Therefore, a series of percussion tests using Hopkinson bar system was carried out to assess the fragmentation performance against the beat rate and spacing of a drill bit. First, single percussion test complemented with numerical simulation was performed to analyze rock fragmentation phenomenon and to describe the fragmentation process. Next, multiple percussion test that repetitively strike the rock sample moving at predetermined rate was carried out to predict drilling efficiency against the button spacing. After the tests, the fragmented volume of the rock was measured by laser scanner and the drilling performance was analyzed using the calculated percussive energy and measured negative volume. Based on the results, the single impact performance of drill bit with 102 mm diameter was predicted.