Abstract

KARAMAN, K.. Evaluation of different surface characteristics and mineral grain size in the estimation of rock strength using the Schmidt hammer. J. S. Afr. Inst. Min. Metall. [online]. 2024, vol.124, n.4, pp.173-184. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2325/2024.

This study investigated the effect of surface roughness on Schmidt rebound hardness (R_l). Four different test surfaces of rock samples were studied: natural, ground, cut surfaces, and core samples. There was significant variability of standard deviation based on the R_l on the natural surface, which indicated high roughness of the rock surface, whereas surface polishing caused a significant decrease in standard deviation. ISRM and ASTM methods were compared to estimate unconfined compressive strength (UCS) for different testing surfaces. R_l obtained from the cut surface was found to be more reliable than those obtained from other testing surfaces for the prediction of UCS; however, regression and ANOVA analyses revealed that the ISRM method gave a more accurate UCS estimation of rocks with highly rough surfaces. It was also shown that R_l values obtained from a cut surface were significantly higher than those obtained from core samples. Therefore, a comparison between R_l values obtained from core samples and cut surfaces was made based on previous studies. This study statistically showed that estimated UCS values are not statistically significant if Schmidt rebound tests are not performed on similar surfaces. In addition, the mineral grain sizes of the studied rocks, different testing surfaces compared with those in literature, and standard deviation from R_l are evaluated and discussed. The Schmidt hammer technique is a rapid, inexpensive, and straightforward method for estimating UCS for preliminary assessment; however, roughness of the surface should be eliminated if variations are shown in the surface rebound hardness.

Keywords : Schmidt hammer technique; unconfined compressive strength estimation; surface roughness; mineral grain size.

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