From cyclic sand ratcheting to tilt accumulation of offshore monopiles: 3D FE modelling using SANISAND-MS

Abstract

Serviceability criteria for offshore monopiles include the estimation of long-term, permanent tilt under repeated operational loads. In the lack of well-established analysis methods, experimental and numerical research has been carried out in the last decade to support the fundamental understanding of monopile–soil interaction mechanisms, and the conception of engineering methods for monopile tilt predictions. With a focus on the case of monopiles in sand, this work shows how step-by-step/implicit, three-dimensional (3D) finite-element (FE) modelling can be fruitfully applied to the analysis of cyclic monopile–soil interaction and related soil deformation mechanisms. To achieve adequate simulation of cyclic sand ratcheting and densification around the pile, the recently proposed SANISAND-MS model is adopted. The link between local soil behaviour and global monopile response to cyclic loading is discussed through detailed analysis of model prediction. Overall, the results of numerical parametric studies confirm that the proposed 3D FE modelling framework can reproduce relevant experimental evidence about monopile–soil interaction, and support future improvement of engineering design methods.

Large diameter laterally loaded piles in sand: Numerical evaluation of soil stress paths and relevance of laboratory soil element testing

“…Values of parameters used in the memory surface constitutive model (Liu et al, 2021 of principal stress axes within the soil around the pile is expected to occur (i.e. Andersen et al 2013, Yang et al 2022.…”

“…The 3D FE model has been built in the Opensees software (McKenna, 1997) following a procedure already adopted and thoroughly tested by Corciulo et al (2017), Kementzetzidis et al (2019), Cheng et al (2021) and Liu et al (2021). The overall dimensions of the soil domain are 70 m × 35 m × 47 m to minimise the effect of the boundary conditions on the stress distribution in the soil adjacent to the monopile, as shown in Corciulo et al (2017) and Liu et al (2021). The pile is modelled as a linear-elastic 3D hollow cylinder represented by a Young's modulus, 𝐸 = 200 GPa, the unit weight of steel, 𝛾 𝑠 = 77 kN∕m 3 and Poisson's ratio, 𝑣 = 0.30.…”

“…The soil behaviour has been modelled using the enhanced version of critical state, bounding surface, kinematic hardening SANISAND2004 constitutive model (Dafalias and Manzari, 2004), named SANISAND-MS. The adopted monotonic values of the soil constitutive parameters are the same with those proposed by Liu et al (2019Liu et al ( , 2021 for Karlsruhe sand, as summarised in Table 1. Successful application of the SANISAND-MS model to a 3D FE analysis of a monotonically loaded monopile-soil interaction system was done by Liu et al (2021).…”

“…The adopted monotonic values of the soil constitutive parameters are the same with those proposed by Liu et al (2019Liu et al ( , 2021 for Karlsruhe sand, as summarised in Table 1. Successful application of the SANISAND-MS model to a 3D FE analysis of a monotonically loaded monopile-soil interaction system was done by Liu et al (2021). The soil is considered to respond in drained conditions and an effective soil unit weight 𝛾 ′ = 9.4 kN∕m 3 was also considered.…”

Enhancement of a high‐cycle accumulation model by an adaptive strain amplitude and its application to monopile foundations

“…An example for a suitable conventional model for high-cyclic loading is the memorysurface enhanced Sanisand model proposed by Liu et al, 9 which is also suitable to model monopiles under lateral cyclic loading. 10 But due to the restrictions mentioned in the two previous raised points, constitutive models such as the HCA model are still necessary for the incorporation of a larger number of loading cycles in complex BVPs with a large number of degrees of freedom (dofs).…”