In the CERCHAR abrasivity test for rocks, to understand the wear process of styli is important for the appropriate setting of test conditions and for the estimation of bit wear in in-situ rock excavation. In this study, the wear process of a stylus was estimated from both the stylus vertical displacement measured during the test and the groove depth measured after the test. The results showed that the stylus wear during the test can be traced with a simple calculation of the measured values for the two high abrasive rocks, Inada granite and Iwaki sandstone. In those tests, the styli were worn flatly. The calculation was corrected for the other medium to low abrasive eight rocks, because the measured groove depth was not thought to be completely consistent with the penetration depth of the stylus. Comparing the results of the nine rocks with the exception of the granite, the stylus wear continued for longer sliding distance in the tests for higher abrasive rock. It was found from the results of the granite that the mineral constitution affected the wear process of the stylus. In addition, this paper discussed the relation of the CAI (CERCHAR Abrasivity Index) and its variation to the stylus wear process and the rock hardness. On the basis of the results, points of attention in the CERCHAR test were described.
