Fractional-Order Elastoplastic Modeling of Sands Considering Cyclic Mobility

Seabed soil may experience a reduction in strength or even liquefaction when subjected to cyclic loadings exerted by offshore structures and environmental loadings such as ocean waves and earthquakes. A reasonable and robust constitutive soil model is indispensable for accurate assessment of such structure-seabed interactions in marine environments. In this paper, a new constitutive model is proposed by enriching subloading surface theory with a fractional-order plastic flow rule and multiple hardening rules. A detailed validation of both stress- and strain-controlled undrained cyclic test results of medium-dense Karlsruhe fine sand is provided to demonstrate the robustness of the present constitutive model to capture the non-associativity and cyclic mobility of sandy soils. The new fractional cyclic model is then implemented into a finite element code based on a two-phase field theory via a user subroutine, and a numerical case study on the response of seabed soils around a submarine pipeline under cyclic wave loadings is presented to highlight the practical applications of this model in structure-seabed interactions.

Automated summary

A new constitutive model incorporating fractional plastic flow rule and multiple hardening rules is proposed and validated with medium-dense sand cyclic test results, demonstrating robustness in capturing non-associativity and cyclic mobility of sandy soils. The model is implemented into a finite element code for a numerical case study on seabed soils under cyclic wave loadings, showcasing its practical applications in structure-seabed interactions.