The effect of mineralogical parameters on the mechanical properties of granitic rocks

By S. Cowie, G. Walton. Engineering Geology, 2018

87 citations recorded by the source corpus.

Abstract The mechanical properties of a given rock volume are dependent on its geological composition. Being able to predict these mechanical properties based on mineralogical parameters could prove useful in engineering and construction settings. The aim of this study is to propose relationships between mineralogical parameters and mechanical properties of granitic rocks. Furthermore, relevant correlations proposed previously in literature were analyzed within the context of a larger dataset. An extensive literature search was performed to compile a database of laboratory compression testing data for granitic rock. Mineralogical parameters and mechanical properties of 58 distinct granitic rock types from 12 countries were analyzed in order to obtain a more complete view of their interrelationships. The following geological properties were compiled: grain sizes (overall and mineral-specific), modal percentages of minerals (quartz, alkali feldspar, plagioclase, and micas), density, and average Mohs Hardness. The following mechanical properties were assessed: Unconfined Compressive Strength (UCS), Brazilian Tensile Strength (BTS), crack initiation stress (CI), crack damage stress (CD), Young's Modulus (E), Poisson's ratio (ν), and the Hoek-Brown constant, mi. The modal percentage of mica minerals was found to have a strong negative correlation with crack initiation stress, crack damage stress, and tensile strength. Additionally, minimum overall grain size is strongly correlated with the CD/CI ratio. A multivariate regression analysis utilized various combinations of five independent variables (minimum overall grain size, average overall grain size, standard deviation of overall grain size, quartz modal percentage, and mica modal percentage) to predict CI, CD, and tensile strength. Multivariate analysis showed that the use of two geological predictor variables typically improved models for CI, CD, and BTS; however, the addition of further predictor variables produced minimal additional improvement. The most important finding of this analysis was that joint consideration of mica modal percentage and grain size parameters allows for improved predictions of CI, CD, and tensile strength to be made for granitic rock. Additionally, it was found that correlations proposed previously in literature appear to be spurious when considered in the context of the larger data set compiled in this research. This occurrence is most likely a consequence of unknown additional variables (confounding variables) that is correlated to both the independent and dependent variables used in forming the original correlations.

Subfields: Management, Monitoring, Policy and Law, Mechanics of Materials

View Paper: https://www.semanticscholar.org/paper/5bd608b41a66d09dc0163843dd936943a42f0f44