Banca de QUALIFICAÇÃO: PEDRO JULIO CASTRO DOS SANTOS

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : PEDRO JULIO CASTRO DOS SANTOS
DATE: 25/11/2025
TIME: 10:00
LOCAL: sala do PEC
TITLE:

Physical-Mechanical Behavior of Sediments from the Barreiras Formation in the east Coast of Northeastern Brazil

KEY WORDS:

Triaxial compression. Grain size distribution. Consolidation. Permeability. Chemical and mineralogical analyses. Iron oxides.

PAGES: 30
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Geotécnica
SUMMARY:

The Barreiras Formation represents one of the most prominent geological units along the northeastern Brazilian coast and is widely used as a natural support for foundations, slopes, and coastal cliffs. However, its heterogeneous nature and the strong influence of iron oxides on its mineralogical composition result in high geotechnical variability, making the understanding of its behavior essential for engineering purposes. In this context, the aim of this study is to quantify and compare the physical–mechanical behavior of soils from the Barreiras Formation originating from different geotechnical environments, contributing to the advancement of knowledge regarding their strength, deformability, and stability in civil engineering works. The specific objectives include quantifying the physical, chemical, mineralogical, and mechanical parameters of these soils, enabling correlations between the presence of iron oxides and characteristics such as grain size distribution, compressibility, permeability, shear strength, cohesion, and friction angle. Four study sites were investigated: (i) Bananeiras/PB, from a slope with a history of instability; (ii) Caaporã/PB, from the foundation soil of the Cupissura dam; (iii) Natal/RN, from subsurface material at Areia Preta beach, intended for the construction of a building near the shoreline; and (iv) Tibau do Sul/RN, from samples taken from the top of a coastal cliff prone to failure. The methodology included laboratory tests of physical characterization (grain size analysis, consistency limits, and specific gravity), chemical and mineralogical analyses using X-ray fluorescence and diffraction (XRF and XRD), compaction tests, one-dimensional consolidation, permeability, and consolidated undrained triaxial compression (CU). The results indicate that the internal heterogeneity of the Barreiras Formation leads to marked differences in the geotechnical behavior of the studied soils. Bananeiras/PB exhibited the highest iron oxide content (35.3%), reflected in the highest cohesion (c = 104 kPa), the lowest permeability (k = 1.84×10⁻⁶ m/s), and the most pronounced overconsolidated behavior (σ’p = 350 kPa). Caaporã/PB stood out for its highest clay content (44.5%), with elevated preconsolidation stress (σ’p = 250 kPa) and predominantly frictional resistance (φ = 27°). Conversely, the samples from Natal/RN and Tibau do Sul/RN presented higher sand contents and lower shear strength values (with cohesion of 20 and 36 kPa, respectively), greater deformability, and higher permeability, consistent with more porous materials. Therefore, the analyses demonstrated a direct correlation between the increase in iron oxide content and strength gain, as well as between the increase in sandy fraction and higher hydraulic conductivity. These findings reinforce that the safe use of soils from the Barreiras Formation requires localized geotechnical investigations, considering the strong variability associated with depositional conditions, weathering, and the degree of cementation.

COMMITTEE MEMBERS:
Externo ao Programa - 346779 - LEONARDO FLAMARION MARQUES CHAVES - nullPresidente - 1284389 - MARIA DEL PILAR DURANTE INGUNZA
Externo à Instituição - RICARDO NASCIMENTO FLORES SEVERO - IFRN