On the quasi-static granular convective flow and sand densification around pile foundations under cyclic lateral loading

Cuéllar, Pablo; Georgi, Steven; Baeßler, Matthias; Rücker, Werner

doi:10.1007/s10035-011-0305-0

Cited by 84 publications

(33 citation statements)

References 27 publications

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“…5b, G increases dramatically with reducing γ max as expected, and in all cases G reduces slightly during cyclic loading. The results correlated quite well with the observations from scaled model tests with different types of offshore wind turbine foundations [4][5][6]27] and the field measuremens [28]. With the same magnitude of (γ max − γ min ) in Series C, the two-way loading resulted in higher G than the oneway loading in the first few hundred cycles (Fig.…”

Section: Macro-scale Responsessupporting

confidence: 84%

“…Designing foundations for offshore wind turbines is challenging as: (1) these are dynamically sensitive structures in the sense that natural frequencies of these structures are very close to the forcing frequencies [1]; (2) cyclic loading can induce accumulated rotation of foundation but the tolerance for the total rotation at seabed is suggested as low as 0.5° in DNV [2]. The soil-foundation interactions under cyclic lateral loading have been investigated intensively by field tests [3], scaled model tests [4][5][6][7][8][9][10], FEM simulations [11] and DEM simulations [12,13] with majority focused on mono-pile foundations as it is the main type of foundation for offshore wind turbines. Empirical relationships for the foundation tilt or stiffness were derived from the model tests but few attention was drawn on the soil disturbances due to the limitations of monitoring technique.…”

Section: Background and Motivationmentioning

confidence: 99%

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Macro- and micro-mechanics of granular soil in asymmetric cyclic loadings encountered by offshore wind turbine foundations

et al. 2019

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Offshore wind turbine foundations are subject to 10 7-10 8 cycles of loadings in their designed service life. Recent research shows that under cyclic loading, most soils change their properties. Discrete Element Modelling of cyclic simple shear tests was performed using PFC2D to analyse the micromechanics underlying the cyclic behaviours of soils. The DEM simulation were first compared with previous experimental results. Then asymmetric one-way and two-way cyclic loading pattern attained from real offshore wind farms were considered in the detailed parametric study. The simulation results show that the shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes; the rate of increase depends on the strain amplitude, initial relative density and vertical stress. It shows that the change of soil behaviour is strongly related to the variation of coordination number, rotation of principal stress direction and evolution of degree of fabric anisotropy. Loading asymmetry only affects soil behaviours in the first few hundred of cycles. In the long term, the magnitude of (γ max − γ min) rather than loading asymmetry dominates the soil responses. Cyclic loading history may change the stress-strain behaviour of a soil to an extent dependent on its initial relative density. Keywords Discrete element modelling • Cyclic loading • Soil stiffness • Micro-mechanism Abbreviations a Parameter defining the magnitude of fabric anisotropy a max Fabric anisotropy at maximum shear strain a min Fabric anisotropy at minimum shear strain d 50 Diameter at which 50% of the sample's mass is comprised of particles with a diameter less than this value e Void ratio G Shear modulus M max Maximum moments in a load cycle M min Minimum moments in a load cycle and M ult Ultimate moment capacity N c Coordination number t Deviator stress s′ Mean stress γ max Maximum shear strain (shear strain amplitude) of a cyclic simple shear test γ min Minimum shear strain in a cyclic simple shear test ζ c Ratio of minimum moment to the maximum moment η c Parameter defined to quantify the degree of asymmetry of cyclic loading θ a Direction of the principal fabric σ Vertical stresses on the sample in a cyclic simple shear test τ max Shear stress at maximum shear strain τ min Shear stress at minimum shear strain * Liang Cui

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Section: Macro-scale Responsessupporting

confidence: 84%

Section: Background and Motivationmentioning

confidence: 99%

Macro- and micro-mechanics of granular soil in asymmetric cyclic loadings encountered by offshore wind turbine foundations

et al. 2019

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“…This indicated that the extent of the densified region was significantly smaller for 1w and unbalanced 2w lateral loading (as compared with balanced 2w lateral loading), consistent with the experimental observations reported by Brown et al (1988). Further, the size of the depression cones observed (applying up to 42% of the ultimate static lateral load-carrying capacity of the pile, P u ) were in broad agreement with the experimental observations from model studies on monopiles embedded in saturated dense sand beds reported by Cuéllar et al (2012). & From the experimental investigations, the discusser concurs that the main reason for the measured/computed increase in secant stiffness with cycling is convective sand flow and the resulting densification around the monopile, most likely due to cyclic shear deformation of the soil mass adjacent to the pile, which causes a net contraction of the sand to occur (Gudehus, 2000).…”

supporting

confidence: 89%

Discussion: Soil–monopile interactions for offshore wind turbines

Cui¹,

Bhattacharya²,

O’Kelly³

2017

Proceedings of the Institution of Civil Engineers - Engineering

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“…It can also be observed that vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to the relative density of soil. The results correlated quite well with the observations from scaled model tests with different types of offshore wind turbine foundations [2,3,7]. The only abnormal trend observed is that the accumulated vertical strain decreases with increasing vertical stress.…”

Section: Experimental Testssupporting

confidence: 79%

Micromechanics of soil responses in cyclic simple shear tests

2017

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Abstract. Offshore wind turbine (OWT) foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a) Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b) Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c) Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number) were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

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On the quasi-static granular convective flow and sand densification around pile foundations under cyclic lateral loading

Cited by 84 publications

References 27 publications

Macro- and micro-mechanics of granular soil in asymmetric cyclic loadings encountered by offshore wind turbine foundations

Macro- and micro-mechanics of granular soil in asymmetric cyclic loadings encountered by offshore wind turbine foundations

Discussion: Soil–monopile interactions for offshore wind turbines

Micromechanics of soil responses in cyclic simple shear tests

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