چكيده انگليسي :
Hardness, as one of the inherent characteristics of rocks, indicates the resistance of the rock to permanent deformation, scratch, and penetration. The hardness has a significant relationship with the rock parameters and therefore, is a good tool for analyzing the machinability of rocks. The application of the Leeb dynamic hardness method in rocks, which is utilized in metallic materials according to ASTM-A956-06, was investigated in this thesis. To achieve this goal, the results in six phases include a comprehensive review of hardness methods in rock engineering, the conditions for using the Leeb method on a laboratory scale, the presentation of a new classification of rock hardness, the effect of texture, prediction of the dynamic elastic constants of the rocks, and finally the effect of surface roughness on the Leeb hardness are presented. After the literature review, the correlations between different methods of the dynamic hardness of rocks with physical and mechanical parameters have been analyzed using regression analysis. The results showed that the minimum thickness and length-to-diameter ratio of block and core samples for the Leeb test are 5 cm and 1.6, respectively. Also, the relationships between two physical parameters, including porosity and density with Leeb hardness, show the relatively significant effects on Leeb hardness. Due to the Mohs hardness method as the most basic and accurate hardness measurement method in experimental studies, the qualitative classification of Leeb hardness was performed based on this hardness method. Based on comparative studies, rock hardness is classified into six different categories based on the Leeb hardness method: Extremely Soft (1-250), Soft (250-450), Moderately Soft (450-750), Moderately Hard (750-850), Hard (850-920), and Extremely Hard (920-1000). Careful study of the relationship between geomechanical properties and texture properties of rocks is essential for almost any type of analysis in rock engineering projects. To analyze the texture properties of the rocks, microphotographs taken from 33 rock samples were analyzed using ImageJ software. Four basic characteristics, including grain perimeter, grain area, and length of minor and major axes, were measured. Next, seven textural quantities, including equivalent diameter, grain compactness, shape factor, aspect ratio, interlocking index, grain size homogeneity index, and texture coefficient, were calculated based on those basic parameters and were statistically analyzed. The results show that the Leeb dynamic hardness increases with increasing the equivalent diameter, grain compactness, grain size homogeneity index, grain interlocking, and texture coefficient. In contrast, Leeb's hardness decreases with increasing the aspect ratio and shape factor. The results also indicate the high effect of texture coefficient on Leeb hardness compared with other textural properties in both sedimentary and igneous rocks. In addition, the relationships between ultrasonic wave velocities and dynamic elastic constants with the Leeb hardness were investigated. Thereafter, by determining the rock quality index (IQ) using microscopic studies and by analyzing the quality index-porosity plot, the variation of the Leeb hardness values was studied. The results of the analyses show that, in both igneous and sedimentary rocks, the dynamic modulus of elasticity has significant correlations with the Leeb hardness. based on the microscopic studies, it was observed that the existence of the porosity in sedimentary rocks and intercrystalline and intracrystalline fissures in igneous rocks sharply reduce the Leeb hardness. Finally, it was found that for studied rock samples with Ra <2μm, the Leeb hardness test (D-type) can be used properly.
