Influence of Pile Diameter and Aspect Ratio on the Lateral Response of Monopiles in Sand with Different Relative Densities

Abstract

The large-diameter monopiles are the most preferred foundation used in offshore wind farms. However, the influence of pile diameter and aspect ratio on the lateral bearing behavior of monopiles in sand with different relative densities has not been systematically studied. This study presents a series of well-calibrated finite-element (FE) analyses using an advanced state dependent constitutive model. The FE model was first validated against the centrifuge tests on the large-diameter monopiles. Parametric studies were performed on rigid piles with different diameters (D = 4–10 m) and aspect ratios (L/D = 3–7.5) under a wide range of loading heights (e = 5–100 m) in sands with different relative densities (Dr = 40%, 65%, 80%). The API and PISA p-y models were systematically compared and evaluated against the FE simulation results. The numerical results revealed a rigid rotation failure mechanism of the rigid pile, which is independent of pile diameter and aspect ratio. The computed soil pressure coefficient (K = p/Dσ′v) of different diameter piles at same rotation is a function of z/L (z is depth) rather than z/D. The force–moment diagrams at different deflections were quantified in sands of different relative density. Based on the observed pile–soil interaction mechanism, a simple design model was proposed to calculate the combined capacity of rigid piles.

Ultimate soil resistance of the laterally loaded pile in uniform sand

“…Considering that the soil failure modes of fixed-head flexible pile are similar to that of the free head (i.e., wedge failure at shallow and flow around at deep zone), no further simulation was performed under this condition. The pile configurations were selected to cover the applications in existing and future offshore wind projects, i.e., D > 6 m and L/D < 8 (Negro et al 2017;Wang et al 2021a, b). The loading eccentricity is 5 m in all cases, since existing studies show that pile-soil interaction is not affected by the loading eccentricity (Klinkvort 2013;Wang et al 2022).…”

“…The constitutive model has been implemented in Abaqus by the user-defined subroutine (Gudehus et al 2008) and used in different applications (e.g., Ng et al 2013). In this study, the model parameters (summarized in Table 3) for Toyoura sand were adopted, which have been calibrated against element test (Hong et al 2016) and validated against centrifuge pile test in medium dense sand (D r = 65%) (Wang et al 2021a(Wang et al , 2021b(Wang et al , 2022. Details about the sand, model calibration, and validation can be found in Ishihara (1993)…”

Lateral Bearing Capacity of a Hybrid Monopile: Combined Effects of Wing Configuration and Local Scour

“…The steel winged monopiles are assumed to be linearly elastic with Young's modulus E p = 210 GPa and Poisson's ratio ν p = 0.3, similar to previous studies on pile foundations [27][28][29]. The Young's modulus of sand E s for describing the elastic behavior is stress-dependent and increases with the earth pressure at rest [30]:…”

“…The "hard contact" model allows separation in the normal direction, while the Coulomb friction model is adopted in the tangential direction. The interface friction angle δ is taken as 2/3ϕ 0 to simulate the typical steel-sand contact property [29,42], where ϕ 0 is the constant friction angle. The value of ϕ 0 can be estimated according to the formula recommended by API [43]:…”

Instability and Failure of Subsea Structures

“…By using the finite-element method, incorporating a state-dependent constitutive model of sand, the influence of pile diameter and aspect ratio on the lateral response of monopiles was numerically investigated [3]. It was revealed that the rotation failure mechanism of a rigid pile is independent of pile diameter and aspect ratio.…”