Abstract
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.
Highlights
In recent decades, considerable efforts have been devoted to the study of structure– seabed interactions in marine environments [1]
Great success has been achieved by considering the seabed as elastic in the simulation of structure–seabed interactions in marine environments [11,12], the development of elasto-plastic constitutive models that can reasonably mimic the behavior of soils under complex cyclic loadings has attracted enthusiastic interest recently [13,14,15,16], especially for sandy soils whose liquefaction behavior under cyclic loading is considered to have a great effect on the stability and serviceability of marine structures
A fractional cyclic constitutive model is proposed by incorporating a novel fractional-order plastic flow rule
Summary
Considerable efforts have been devoted to the study of structure– seabed interactions in marine environments [1]. Dafalias [17] introduced the well-known bounding surface plasticity model as an efficient tool for capturing the rate-independent mechanical behavior of geomaterials It was widely accepted and gradually enriched by many other researchers [21,22,23,24] to replicate the static and cyclic behaviors of both loose and dense sandy soils. The cyclic mobility model is able to describe the behavior of sands with different densities using one same set of material parameters and mimic the cyclic mobility (e.g., butterfly-shaped stress path) of sands upon liquefaction under cyclic loadings In spite of these abundant constitutive models based on different plastic theories, further model evolution for sands under cyclic loadings is still required to reasonably consider the non-associated, state-dependent (pressure, density) behaviors and the cyclic mobility under undrained relaxation of mean effective stress. The new fractional cyclic model, coded into a user subroutine, is implemented into a finite element code based on a two-phase field theory [31], and the response of soils around a submarine pipeline under cyclic wave loadings is studied through large-scale numerical simulation
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