Experimental Characterization and Elastoplastic Constitutive Modeling of a Phyllite Residual Soil

Abstract This article investigates the experimental and elastoplastic properties of a phyllite residual soil collected from the abutment of a tailings dam located in Brazil’s Iron Quadrangle–a region renowned for its extensive iron ore mining and associated geotechnical infrastructure. Given that phyllite residual soils are not well documented and that they are characterized by pronounced heterogeneity and anisotropy that evolve over time, it is essential to define their specific geotechnical parameters and develop accurate constitutive models. Through a series of laboratory tests–including physical characterization, oedometer consolidation as well as drained and undrained triaxial compression–key properties of the phyllite soil were identified, such as its compressibility, deformability, shear strength, yield surface, plastic potential, and hardening behavior. Regarding plasticity, a tear-drop shaped yield surface was established based on iso-plastic work contours, while an elliptical plastic potential was defined according to the orientation of plastic strain increments. Additionally, an exponential hardening law was adopted to characterize the material’s hardening behavior. Finally, a numerical simulation was performed to model an undrained triaxial compression test on a phyllite sample using the proposed elastoplastic framework. The results demonstrated that the model successfully reproduced the overall response of the phyllite soil, capturing both positive and negative excess pore water pressure developments as well as the characteristic strain-hardening, strain-softening and elastic-perfect plastic behaviors. All these findings offer valuable data for advancing constitutive modeling of this material.