Controls of lithology and degree of fracturing on the in-situ estimation of rock mass hardness using the Equotip hardness tester

The use of the Equotip hardness tester in engineering geology has increased significantly in recent years, especially in estimating the strength of weak and weathered rock materials. Weathering and fracturing, besides lithology, influence the overall behaviour of the rock mass and the response of the non-destructive tester. In this study, more than 9,000 Equotip rebound measurements were collected from twelve rock outcrops of several geological formations in central Italy, using a regular measurement grid approach. In addition, linear scan lines were combined with the analysis of photogrammetric sampling windows to determine geomechanical indexes such as Rock Quality Designation (RQD), Joint Volumetric Count (Jv) and Fracture intensity (P21) to be coupled with the Equotip measurements. A strong correlation was found between RQD, Jv, P21 and the Equotip rebound. The study presents an innovative approach by integrating extensive Equotip rebound measurements with geomechanical indices (RQD, Jv, P21) and advanced photogrammetric techniques. This combination provides new quantitative constraints on the relationship between fracture intensity, lithological variation, and mechanical properties of rock masses. Our findings highlight the potential of Equotip testing as a fast and reliable tool for in-situ rock mass quality assessment, also in heterogeneous geological settings, improving hazard management and engineering design.