<p>Bridge failures caused by lateral forces highlight the importance of accurately modeling caisson foundation behavior, particularly considering soil–structure interaction and interface nonlinearities. Traditional Winkler models, such as the widely used four-spring model by Gerolymos and Gazetas, often fall short in capturing these effects, especially sliding and separation at the soil–caisson interface, despite their simplicity and ease of use. This study addresses these limitations by developing modified empirical equations for Winkler spring constants that explicitly account for interface nonlinearity. The proposed model incorporates variations in soil type, caisson geometry, and loading conditions. Finite element analyses are performed on a solid circular caisson embedded in homogeneous soil, subjected to vertical, lateral, and moment loads, while including both soil and interface nonlinearities. Results from the finite element simulations are used to optimize and derive improved spring constant equations. Validation against 3D finite element models demonstrates that the proposed approach reliably predicts lateral load–deformation and moment–rotation responses of circular caissons. Furthermore, the model proves effective under dynamic and seismic loading scenarios. The proposed model offers a significant improvement in accuracy over existing methods while remaining computationally efficient and free from complex parameter calibration. It provides a practical, robust tool for caisson foundation design, enhancing the resilience and safety of bridge structures under lateral loading.</p>