Spatial variability of the mechanical properties of sediments from the Barreiras Formation on the eastern coast of northeastern Brazil

Abstract

The Barreiras Formation constitutes one of the most relevant geological units along the northeastern Brazilian coast, being widely used as a natural support for foundations, slopes, and escarpments. However, its lithological heterogeneity and the variable presence of different minerals result in significant geotechnical variability, requiring a detailed understanding of its mechanical behavior for engineering applications. This study aims to quantify and compare the mechanical behavior of Barreiras Formation soils from distinct geotechnical and geomorphological contexts, as well as to correlate the presence of iron oxides with physical and mechanical properties, including grain-size distribution, compressibility, permeability, and shear strength. Soil samples were collected from Bananeiras/PB, Caaporã/PB, Natal/RN, and Tibau do Sul/RN. The methodology included physical characterization tests, mineralogical and chemical analyses by X-ray diffraction (XRD) and X-ray fluorescence (XRF), as well as compaction, one-dimensional consolidation, permeability, and consolidated undrained (CU) triaxial tests. The results revealed significant differences in the mechanical behavior of the analyzed soils. The material from Bananeiras/PB showed a high iron oxide content, associated with high cohesion, low permeability, and a pronounced overconsolidated behavior. The soil from Caaporã/PB was characterized by a higher clay content, high preconsolidation stress, and predominantly frictional strength. In contrast, the soils from Natal/RN and Tibau do Sul/RN exhibited a higher sand fraction, greater permeability, and lower shear strength, indicating less cemented structures and greater susceptibility to deformation.