An investigation on sample size in Leeb hardness test and prediction of some index properties of magmatic rocks

Abstract

The first aim of this study is to determine the effect of the sample size on the Leeb hardness (HL), which is a non-destructive test, in magmatic rocks. For this scope, cubic samples with edge lengths of 3, 4, 5, 6, 7, 8, 9, and 10 cm from 15 different magmatic rocks (igneous, volcanic, and pyroclastic) were prepared, and variations of the HL values were measured. Based on the results, it was determined that as the strength values of magmatic rock samples increase, the effect of sample size on HL value decreases. Additionally, the minimum sample size, at which the HL value did not change, was found to be 7 cm. The second aim of this study is to examine the correlation between the HL values of the rocks’ minimum sample size, and the index properties were examined by the simple regression method. For this purpose, 76 various types of magmatic rock samples were tested in the laboratory in order to determine their dry and saturated HL values and index (P-wave velocity, dry density, porosity, and uniaxial compressive strength) values. The relationship between the dry and saturated HL values and the index properties of the samples was examined by simple regression analysis. Based on this analysis, a strong linear relationship was found between the index properties. In addition to this, a strong exponential relationship was determined between the dry and saturated HL and uniaxial compressive strength (UCS) values of these rocks, and the determination coefficients (R2) were found to be 0.85 and 0.86, respectively. The Leeb hardness test can be used as a non-destructive method where a regular-shaped rock sample is difficult to obtain (in rocks and/or historical structures) and to estimate the rock properties practically in the laboratory and field.