Banca de DEFESA: PAULA DE MOURA ESTEVAO PEROBA

Mechanical Behavior of Compacted Gabbroic Residual Soil

Saprolitic soil, gabbro, geotechnical characterization, shear strength, dilatancy

Abstract: The mechanical behavior of a saprolitic soil, originating from gabroic rock formations covering an area of approximately 31 km² in a semi-arid region of Brazil, was investigated. The study involved the collection of data from petrographic, chemical (XRF), and mineralogical (XRD) analyses, as well as a series of physical (geotechnical characterization and compaction), hydraulic (permeability), and mechanical (triaxial and consolidation) tests. The results indicated that the soil originates from a gabronorite and exhibits non-plastic behavior, with an SUCS classification of SW-SM. It is characterized by low permeability and low compressibility. During compaction tests, the soil displayed a propensity for grain breakage; however, it was not possible to fully characterize this phenomenon within the scope of the conducted tests. The mechanical tests revealed that the yield stress imposed by compaction made the soil's behavior resemble that of an overconsolidated soil. This led to the generation of negative pore pressures, increasing the soil's strength in undrained tests, and a dilatant behavior in drained tests, where the dilatant tendency decreased as the effective confining stress increased. Under higher confinement stresses, the behavior shifted to a contractive state, and reaching peak strength was followed by a significant reduction in strength due to the continuous increase in positive pore pressure – a behavior trend that could be unfavorable for some geotechnical applications.