Advanced numerical modelling of slab-subgrade interaction with uplift using an augmented Lagrangian Mortar FEM approach

Accurate representation of slab–subgrade interaction under partial contact is essential for evaluating rigid pavement response. This study develops an Augmented Lagrangian Mortar Finite Element Method (AL-MFEM) for modelling unilateral slab–subgrade contact and separation, combining augmented Lagrangian constraint enforcement with mortar discretisation to accommodate evolving contactregions and non-matching interfaces. Parametric analyses examined the effects of foundation stiffness, load magnitude and load position on slab displacement, contact pressure, uplift and bending response. The formulation was quantitatively validated against the Westergaard interior-loading solution for the full-contact benchmark, followed by numerical investigation of partial-contact cases. The results indicate pronounced sensitivity of separation and contact-pressure redistribution to support stiffness and load eccentricity, while increasing load magnitude reduced separation within the investigated configurations. Mesh and computational assessments demonstrated stable numerical behaviour. The framework provides a mechanistic basis for analysing slab–subgrade separation and future extension to jointed, layered, nonlinear and dynamically loaded pavements.