Numerical investigation on bearing capacity of circular shallow foundations under different drainage conditions

Circular shallow foundations that support offshore structures suffer from superstructure loading, with drainage changes significantly affecting bearing capacity. However, previous studies on bearing capacity primarily focused on the undrained condition, neglecting the effect of drainage conditions. To address this gap, finite element analysis using the Modified Cam-Clay (MCC) model is conducted to evaluate bearing capacity under varying drainage conditions, considering the effect of soil heterogeneity and foundation roughness. Surrounded soil responses, including evolution in excess pore pressure, stress paths, soil strength and failure mechanism, are analyzed to interpret the capacity changes. The results show that the drainage conditions significantly influence the bearing capacity. The capacity gain and soil response variation induced by drainage are amplified by an increase in the soil heterogeneity, while foundation roughness has a limited effect. The proximity to the free drainage surface is a key determinant of the drainage-induced alteration in soil response, as it determines the path length for pore pressure dissipation. Based on these findings, predictive expressions are developed to estimate bearing capacity across drainage conditions, incorporating the effect of soil heterogeneity and foundation roughness.