Quantifying the effects of vein mineralogy, thickness, and orientation on the strength of intact veined rock

Abstract

The presence of veins in the rock matrix influences the behaviour of a rock. This results in a behaviour that is distinct from intact rock without any veins and structure and from jointed rock. In this context, intact veined rock is a rock containing mineral veins and no joints. This paper investigates the influence of vein mineralogy, thickness, and orientation on the strength of intact veined andesite from the El Teniente mine. This investigation has focused on a comprehensive vein characterization and analyses of the results of triaxial compression experiments.In a comprehensive laboratory investigation, it was demonstrated that the peak strength of intact veined rock specimens was strongly influenced by the orientations of individual veins, whereby vein mineralogy and thickness had a lesser role. A further analysis of the mineral composition of the intact veined rock specimens following a series of triaxial tests revealed a more dominant influence of the mineral composition of the veins. It was shown that rock specimens dominated by veins containing <30% of hard minerals, i.e. minerals with Moh's hardness>4, attained significantly lower peak strengths than specimens where the average content of hard minerals exceeded 60% of the vein infill. Analyses of the mobilised shear strength of individual veins demonstrated a strong correlation between the presence of hard minerals and the strength of individual veins in the rock specimens. This relationship was stronger when the vein volumetric content of hard minerals was <40–50%. For veins, in which the hard mineral content exceeded the 40–50% threshold, the estimated strength values were influenced by mineral content to a lesser degree.