Influence of Weathering on the Engineering Properties of Dacites in Northeastern Turkey

Abstract

The purpose of this study is to investigate dacites of different weathering grades from the Cakmakkaya and Damar open-pit copper mines in northeastern Turkey based on their mineralogical, petrographical, and geomechanical characteristics. The dacites for which surveys are carried out are mainly subjected to chemical weathering as well as physical disintegration and hydrothermal alteration. Discontinuities in this rock appear to be a major influence on the spatial distribution of weathering profiles, with the intensity of weathering increasing in the plagioclase phenocrystals and microlites as the weathering grade increases. The present results show that the type and amount of clay minerals increase as the weathering grade increases. As the weathering increases, the amount of mobile oxides, such as Na2O, MgO, and CaO, decreases while Fe2O3 and the loss on ignition (LOI) content increase for most of the dacite samples. The microfracture frequency () may be a good indicator of fabric changes, and methylene blue adsorption (MBA) test and LOI may be good indicators of chemical weathering for the dacites. Geomechanical laboratory tests indicate that the strength of the samples is controlled by weathering. Field observations and mineralogical analyses show that the effects of weathering are critical for slope stability.