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

1. Ahmed Elkadi, PhD, CEng
Simulation of Installation of MONopiles using MPM

2. (Mono)pile Installation
Effects
• Motivation
• Numerical approach: Material Point Method
• SIMON project
Contents

3. Global capacity trends
D=4m
D>9m
L>80m
2016 Offshore Wind Technologies Market Report

4. Global substructure trends
D>9m
L>80m
2016 Offshore Wind Technologies Market Report

5. Monopiles XXL
D=4m
D>9m
L>80m

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. (Mono)pile installation effects
Innovative Installation methods
source: Fistuca.com
Gentle Driving of Piles
Source: grow-offshorewind.nl

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. (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. 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. MPM – Material Point Method
http://www.mpm-dredge.eu/

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. 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. displacements Stresses
Pile driving with MPM (Al-Kafaji, 2013)
m
h
v 2 g h
tpulse
fmax
f (t)
t
tperiod
dynamic loading

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. Jacked installation: results (MPM)
Horizontal effective stress during installation at 40g

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. Jacked installation: Experimental vs numerical
static load test
loose sand medium dense sand
Computers and Geotechnics 73 (2016) 58–71

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. 2015 FLOW NS-VIP project
Extend Cuxhaven study through numerical analyses of pile installation.
Source: VIBRO

21. Soil density in cross-section
Stresses during lateral loading,
installation effects considered
NS-VIP 2015

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
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. 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. Dimensions of the centrifuge set-up
Pile driving in centrifuge
Stoevelaar et al. (2011)

26. Sample properties
Pile driving in centrifuge
• Baskarp sand is used

27. Background mesh
Pile driving in centrifuge
Pile
Soil
~ 9000 linear triangle elements

28. Material point discretisation
Pile driving in centrifuge
Uniform distribution of material points
~ 48000 material points

29. Pile driving in centrifuge
Experiment (tip stress)
DR = 38% DR = 66%

30. Impact Hammered Pile
Background
30

31. Impact Hammered Pile
Model
2D Axisymmetric MPM Model

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. Impact Hammered Pile
Results: vertical displacement (DR = 40%)

34. Impact Hammered Pile
Results: radial displacement (DR = 40%)

35. Impact Hammered Pile
Results: vertical stress (DR = 40%)

36. Impact Hammered Pile
Results: radial stress (DR = 40%)

37. Thank you for your attention!