New Charts for Assessing the Compressive Strength of Rock Materials Using the Leeb Hardness Test

Binal A., Erol Ö.

Rock Mechanics and Rock Engineering, ss.1-22, 2026 (Hakemli Dergi)

Özet

This study assessed the use of Leeb rebound hardness (HL) to estimate the uniaxial compressive strength (UCS) of intact rock samples, with a particular focus on weak pyroclastic rocks, where traditional Schmidt hammer impacts may cause damage. A total of 168 NX-diameter cores from 23 rock types were analysed, including 13 ignimbrite varieties, as well as sedimentary, carbonate, and crystalline igneous rocks. The measurements included apparent porosity, dry unit weight, P-wave velocity, Schmidt rebound number, vertical and horizontal Leeb hardness, and UCS. The key innovation is the creation of two practical UCS nomograms that integrate Leeb hardness with dry unit weight, with separate scales for measurements parallel and perpendicular to the core axis. The ignimbrite-specific analyses and charts were based on 65 specimens. The Dirty White ignimbrite specimens were excluded from the ignimbrite-specific analyses, because their thin-section petrographic identification had not been completed sufficiently for confident inclusion in the lithological subset. A second chart was created for the complete 168-specimen multi-lithology dataset. Vertical and horizontal HL values showed systematic differences, although the tests could not fully distinguish the effects of fabric anisotropy from those of texture and surface. In the data, the Leeb hardness correlated more strongly with the UCS than the Schmidt rebound number. Schmidt impacts caused visible crushing and cracking in some weak ignimbrites, whereas similar damage was not observed after single-point Leeb impacts. Literature data served as independent validation of the charts' performance. Overall, these charts should be viewed as practical screening tools for intact, smooth laboratory cores within the tested HL, unit weight, and UCS ranges, and not as universal strength laws or direct replacements for standard UCS tests.