Nonlinear Finite Element Analysis for Geotechnical Problems: Explain the theory behind nonlinear finite element analysis $($FEA$)$ and its relevance in solving complex geotechnical problems. Discuss the challenges associated with modeling soil$-$structure interaction, including material nonlinearity, large deformations, and soil heterogeneity. Explore advanced constitutive models such as elastoplastic and hypoplastic models and their application in simulating soil behavior under different loading conditions. Evaluate the advantages and limitations of nonlinear FEA in predicting soil settlement, slope stability, and foundation response for civil engineering projects.