Evaluation of different surface characteristics and mineral grain size in the estimation of rock strength using the Schmidt hammer
DOI:
https://doi.org/10.17159/Abstract
This study aims to investigate the effect of surface roughness on Schmidt rebound hardness (RL). Accordingly, four different testing surfaces (natural, grinding and cut surfaces and core samples) were studied on rock samples. There was a great variability of standard deviation based on the RL on natural surface, which indicates great roughness of the rock surface whereas surface polishing caused significant decrease in standard deviation. ISRM and ASTM suggested methods were also compared in the estimation of uniaxial compressive strength (UCS) for different testing surfaces. RL obtained from cut surface is more reliable than those obtained from other testing surfaces for the prediction of UCS. However, regression and ANOVA analyses revealed that ISRM method gave the more accurate UCS estimation of rocks having high rough surface. It was also shown that RL values obtained from the cut surface are significantly higher than those obtained from core samples. Therefore, comparison was made between RL values obtained from core samples and cut surfaces based on the 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, mineral grain sizes of the studied rocks, different testing surfaces from the literature and standard deviation from the RL were evaluated and discussed. It is concluded that Schmidt hammer can be viewed as a rapid, inexpensive and simple technique in the UCS estimation for preliminary assessment provided that an experience would be required to evaluate and interpret the readings.
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