Experimental investigation on rock microfabrical effects on dynamic hardness behaviour

Rocks` physicomechanical properties are influenced by their textural qualities. Rock mass stability is largely governed by these variables. Many geoengineering facilities depend on the capability to assess both short and long-term rock behaviors based on the interaction between different textural characteristics and physicomechanical properties. Rock hardness is frequently used in excavation engineering and is measured by several methods with different mechanisms. The Leeb dynamic hardness method has been recently applied in rock engineering applications as a new, inexpensive, non-destructive, and portable technique. This paper aims to show the interaction between the quantitative microfabrical features and the Leeb hardness of the rocks. For this purpose, 33 various rock types were chosen by considering their physicomechanical properties and microfabrical characteristics. Thin sections were prepared and their microphotographs were analyzed by ImageJ software. Four basic characteristics, including grain perimeter and area and length of minor and major axes, were measured. Then, seven textural quantities, including equivalent diameter ( D<sub>equi</sub>), shape factor ( SF), aspect ratio ( AR), grain compactness ( C), texture coefficient ( TC), interlocking index ( g), and grain size homogeneity ( t), were calculated based on those basic parameters and statistically analyzed. The findings indicate that the Leeb hardness increases with increasing the grain area and perimeter, equivalent diameter, grain compactness, homogeneity of grain size, grain interlocking, and TC. In contrast, Leeb`s hardness decreases with increasing the AR and SF. The texture coefficient reveals the most meaningful relationship ( R² > 0.8) with the Leeb dynamic hardness test among the studied microfabrical characteristics in sedimentary and igneous rock samples.