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DSD-NL 2018 Simulation of Installation of Monopiles using MPM - Elkadi

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Presentatie door Ahmed Elkadi, Deltares, op de Geo Klantendag 2018, tijdens de Deltares Software Dagen - Editie 2018. Donderdag, 7 juni 2018, Delft.

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DSD-NL 2018 Simulation of Installation of Monopiles using MPM - Elkadi

  1. 1. Ahmed Elkadi, PhD, CEng Simulation of Installation of MONopiles using MPM
  2. 2. (Mono)pile Installation Effects • Motivation • Numerical approach: Material Point Method • SIMON project Contents
  3. 3. Global capacity trends D=4m D>9m L>80m 2016 Offshore Wind Technologies Market Report
  4. 4. Global substructure trends D>9m L>80m 2016 Offshore Wind Technologies Market Report
  5. 5. Monopiles XXL D=4m D>9m L>80m
  6. 6. (Mono)pile installation effects Installation method jacking Impact driving vibro- driving Fstat Fdyn Fstat (displacement controlled) Fdyn = dI/dt Fdyn = m W ² cos (W t) Fstat
  7. 7. (Mono)pile installation effects Innovative Installation methods source: Fistuca.com Gentle Driving of Piles Source: grow-offshorewind.nl
  8. 8. (Mono)pile installation effects Installation method jacking Impact driving vibro- driving Fstat Fdyn Fstat (displacement controlled) Fdyn = dI/dt Fdyn = m W ² cos (W t) Fstat
  9. 9. (Mono)pile installation effects Installation effects • Change of stress state and void ratio (density) • Induced (excess) pore water pressures • Ground vibrations/noise • Friction fatigue • Settlements in the near field • Influence on adjacent structures Bearing behaviour • Capacity with respect to installation method
  10. 10. Monopile installation effects Pile drivability How does hammer load, vibrator frequency, pile diameter, soil density, influence drivability? Ground response to wind and wave loading How does installation method influence lateral pile-soil stiffness? (for different soil (sand) densities, vibrator frequencies, hammer loads, pile diameters)
  11. 11. MPM – Material Point Method http://www.mpm-dredge.eu/
  12. 12. MPM : brief description UL-FEM : mesh deforms with soil MPM : no severe mesh distortions Integration points Material points UL-FEM : Mesh node locations are updated as material deforms. MPM : Material points representing soil move through fixed mesh.
  13. 13. MPM : decoupling material from mesh Lagrangian Eulerian initial configuration calculation step after resetting the mesh in each step : Equilibrium equations solved at nodes for displacement increments, mapped to material points. All information is stored at the material points.
  14. 14. displacements Stresses Pile driving with MPM (Al-Kafaji, 2013) m h v 2 g h tpulse fmax f (t) t tperiod dynamic loading
  15. 15. Jacked installation: Centrifuge tests for validation • preparation at 1g (pile embedded 10D) • spin-up to 40g (pile still embedded 10D) • installation at 40g  v = 10 mm/min, Dd=10D • static load test at 40g  v = 0.00167 mm/s, Dd=0.1D centrifuge tests at Deltares (Huy, 2008) 10D
  16. 16. Jacked installation: results (MPM) Horizontal effective stress during installation at 40g
  17. 17. Jacked installation: Stress change 0 2 4 6 8 A A’ B B B’ vertical cross section B-B’ horizontal cross section A-A’
  18. 18. Jacked installation: Experimental vs numerical static load test loose sand medium dense sand Computers and Geotechnics 73 (2016) 58–71
  19. 19. 2014 VIBRO project • 3 pile pairs, each of them with a hammered and a vibrated pile in Cuxhaven • Soil investigation before and after installation (CPTs) • Static lateral load tests • Onshore test under Offshore conditions Source: VIBRO
  20. 20. 2015 FLOW NS-VIP project Extend Cuxhaven study through numerical analyses of pile installation. Source: VIBRO
  21. 21. Soil density in cross-section Stresses during lateral loading, installation effects considered NS-VIP 2015
  22. 22. JIP SIMON project  Enhancement/speed up of MPM (including a 2D version)  Understanding and quantifying monopile installation effects  Sensitivity study on pile drivability (vibrated and impact driven)  Sensitivity studies on axial / lateral pile-soil stiffness  Recommendations for optimized and novel pile designs and installation techniques  September 2016 – September 2018
  23. 23. 23 2D axisymmetric MPM • An axisymmetric MPM code has recently been developed for numerical simulations of pile driving. • Number of elements and material points can significantly be reduced compared to 3D simulations. • In 2D axisymmetric, each particle represents one radian of a ring rotated around the axis of symmetry. • Initial mass and volume of particles are multiplied by the radius of the particle. • The rest of formulation of 2D axisymmetric MPM is similar to the 2D axisymmetric formulation of FEM. region to be modelled Galavi et al. (2018)
  24. 24. Interaction between pile and soil is defined using a contact formulation to prevent interpenetration. • Frictional/cohesive contact • Gap and closure • Improved for sharp edges 24 body R body B node Contact formulation Bardenhagen et al. (2000)
  25. 25. Dimensions of the centrifuge set-up Pile driving in centrifuge Stoevelaar et al. (2011)
  26. 26. Sample properties Pile driving in centrifuge • Baskarp sand is used
  27. 27. Background mesh Pile driving in centrifuge Pile Soil ~ 9000 linear triangle elements
  28. 28. Material point discretisation Pile driving in centrifuge Uniform distribution of material points ~ 48000 material points
  29. 29. Pile driving in centrifuge Experiment (tip stress) DR = 38% DR = 66%
  30. 30. Impact Hammered Pile Background 30
  31. 31. Impact Hammered Pile Model 2D Axisymmetric MPM Model
  32. 32. Impact Hammered Pile Soil model parameters (Hypoplastic) • The parameters of Baskarp sand is • Three tests have been done on loose (DR=40%), medium dense (DR=60%) and dense (DR=90%) sand samples.
  33. 33. Impact Hammered Pile Results: vertical displacement (DR = 40%)
  34. 34. Impact Hammered Pile Results: radial displacement (DR = 40%)
  35. 35. Impact Hammered Pile Results: vertical stress (DR = 40%)
  36. 36. Impact Hammered Pile Results: radial stress (DR = 40%)
  37. 37. Thank you for your attention!

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