Effect of scour on the behavior of a combined loaded monopile in sand

Li, Q.; Prendergast, L.J.; Askarinejad, A.; Gavin, K.

doi:10.1201/9781351003629-192

Cited by 6 publications

(3 citation statements)

References 15 publications

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“…The development of OWTs has experienced rapid growth in recent years and is considered the most mature technology to facilitate the energy transition (Li et al, 2018). Monopiles remain the most commonly used foundation to support OWTs accounting for 87% of all installations to 2019 (WindEurope, 2018;Fan et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

Gavin

Askarinejad

et al. 2022

Can. Geotech. J.

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The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased, and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈ 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

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Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

Gavin

Askarinejad

et al. 2022

Can. Geotech. J.

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“…The formation of scour essentially increases the free cantilevered length of a monopile and simultaneously reduces the strength and the stiffness of the soil around the pile due to the lower remaining overburden pressures, potentially compromising the stability of the monopile (Hoffmans and Verheij, 1997;Sumer and Fredsøe, 2012). Several researchers have previously investigated the effect of scour formation on the lateral response characteristics of piles (Li et al, 2018;Prendergast et al, 2013). Reese et al (1989) presented an overview of the scour formation process in cohesive soils, focusing on the gap created at the soil-pile interface due to water injection induced by the cyclic loading.…”

Section: Introductionmentioning

confidence: 99%

Influence of scour depth and type on p–y curves for monopiles in sand under monotonic lateral loading in a geotechnical centrifuge

et al. 2020

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The influence of scour on the lateral response of monopile foundations for offshore wind turbines is investigated in this paper. Application of lateral load-displacement (p-y) curves to predict the lateral pile behaviour is subject to uncertainty as many of the presently used design approaches have been derived for long, slender piles. These piles, with typical length/diameter ratios (L/D) of greater than 10 behave differently compared to rigid monopiles, with L/D typically less than 6. In this paper, centrifuge tests are conducted on a monopile model under various scour scenarios and p-y curves are derived from strain gauges embedded along the model pile wall. Global scour and two different shapes for local scour holes are studied. Using the piecewise polynomial method for extraction of p-y curves from sparsely distributed strain measurements, it is recommended to use a 4th order polynomial for the moment profile to extract soil reaction and a 7th order polynomial for the moment profile to calculate pile deflection. Results indicate that the pile behaviour is significantly influenced by the nature (size, shape) of the scour holes affecting the pile-soil system and suggest that the p-y curves should be appropriately modified to account for this behaviour.

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“…As a consequence, the pile lateral capacity and stiffness could be decreased, potentially resulting in large lateral displacement and rotation. Such effects can put the superstructure at risk through the generation of excessive fatigue loading as well as operational issues (Li et al 2018). The shapes of various types of scour holes are illustrated in Figure 1.…”

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confidence: 99%

Impact of scour on lateral resistance of wind turbine monopiles: an experimental study

Askarinejad

Gavin

2021

Can. Geotech. J.

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The majority of offshore wind structures are supported on large-diameter, rigid monopile foundations. These piles may be subjected to scour due to the waves and currents that causes a loss of soil support and consequently decreases the pile capacity and system stiffness. The results of numerical models suggest that the shape of the scour-hole affects the magnitude of pile capacity loss, however, there is a dearth of experimental test data that quantify this effect. This paper presents a series of centrifuge model tests on an instrumented model pile that investigates the effects of scour-hole geometry on the response of a laterally loaded pile embedded in sand. The pile instrumentation allowed load-displacement and p-y (soil reaction-displacement) curves to be derived. Three scour geometries (global, local wide and local narrow) and three scour depths (1D, 1.5D and 2D; where D is pile diameter) were modelled. For all three scour types, pile moment capacity decreased almost linearly with increase of scour depth. Simple empirical relations were proposed to evaluate the detrimental influence of scour on the pile moment capacity. A new method has been developed to allow designers to quantify the effect of scour-hole shape and severity of scour on the pile response.

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Effect of scour on the behavior of a combined loaded monopile in sand

Cited by 6 publications

References 15 publications

Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

Influence of scour depth and type on p–y curves for monopiles in sand under monotonic lateral loading in a geotechnical centrifuge

Impact of scour on lateral resistance of wind turbine monopiles: an experimental study

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