A 1D macro-element model for suction caissons under inclined loading via scaling from Hardening-Soil relation

Macro-element models treat foundation load-displacement behavior as a macro-scale constitutive law and have been widely developed in foundation design. This study proposes a novel 1D macro-element model for suction caissons in clay under combined vertical-lateral ( V - H ) loading. The key innovations are: (i) the macro-element formulation is derived directly by upscaling a conventional Hardening Soil constitutive model to the caisson scale, ensuring consistency between soil and macro responses; and (ii) the V-H response is represented by a single inclined load-displacement curve rather than separate vertical and lateral components. In this study, a three-dimensional finite element model with the Hardening Soil constitutive law is first established and validated. The FEM model is then used to perform a comprehensive parametric study on caisson responses. Based on the calibration of model parameters, a 1D macro-element model is formulated through direct upscaling of the Hardening Soil constitutive model. The proposed 1D macro-element model is finally validated against existing results from numerical simulations and centrifuge tests. The comparisons show that the proposed model can accurately reproduce the load-displacement response of suction caissons under combined V-H loadings, demonstrating its potential as a fast and practical tool for suction caisson design.