Strain Hardening Monotonic and Cyclic Response of Cohesive Seabed through Bounding Surface Theory

Seabed soils’ stress-strain relationships are nonlinear, and the complexity associated with soil constitutive behavior increases substantially as the loading becomes reversed. This study focuses on the constitutive behavior of cohesive seabed soils under monotonic and cyclic wave loadings. The theoretical framework developed is based on Bounding Surface Plasticity, where soil strain-hardening is addressed through a proposed hardening law to calculate plastic strains and their evolution during the loading history. Considering clays and clay-like cohesive soils located mainly on the surface of the seabed, the plastic hardening modulus is updated using deviatoric plastic strains, and a new degradation function, which is a novel contribution in the study, is developed and incorporated into the theoretical framework. The proposed model, whose mathematical formulation is more practical and simpler compared to other similar models for cohesive seabed soils, is integrated into a computer program using an explicit numerical scheme. Then, several drained and undrained monotonic and cyclic triaxial tests for normally and over-consolidated clays are simulated to verify the proposed constitutive formulation. Results indicate that simulations of cyclic triaxial tests using the proposed model successfully capture the essential static and dynamic behavior of cohesive seabed soils, including large number of load cycles. The proposed model stands out with its predictive power and the simplification advantage it brings to the theory through the hardening law compared to previous models, as successfully demonstrated in this study. The proposed model can be used in solving coastal and offshore geotechnical engineering problems with high accuracy.