Investigation of rock weathering and geochemical changes in road cuts, central expressway

Abstract

Investigation of geochemical changes of different rock types is essential for identifying the degree and intensity of chemical weathering. In this research, three major rock types were identified (granitic gneiss, quartz feldspathic gneiss, and biotite gneiss) and the effect of chemical weathering on them was measured. Identifying the intensity of chemical weathering on these rock types is important to determine the most vulnerable gneissic rock type and to mitigate any risks associated with it at the correct moment. In each rock, three weathering stages were identified (residual soil, weathered rock, and fresh rock) and subjected to AAS and ICP-MS analysis to determine elemental concentrations. Chemical weathering indices such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Weathering Index of Parker (WIP), and Vogt’s Residual Index (V) were calculated according to the depth of rock profiles, and weathering trends were developed. Based on these trends, quartz feldspathic gneiss was identified as the most weathered rock type due to rapid leaching of mobile elements even in fresh rock. LAAV values of each rock type were compared with weathering indices, showing a linear relationship.