DSD-NL 2019 Anura3D ontwikkelingen - Analyse grote deformaties in de geotechniek - Martinelli

G e o K l a n t e n d a g 2 0 1 9 , 2 0 j u n i 2 0 1 9
Anura3D ontwikkelingen: Analyse grote deformaties in de geotechniek
Mario Martinelli

GeoKlantendag2019,20juni2019
2
Outline
• Large deformation analysis - MPM
• Cutting process in layered soils
• Monopile installation
This Photo by Unknown Author is licensed under CC BY-NC-ND

3
Outline

Basic FEM approaches
4
• elements become inaccurate / unstable if distorted too much
• → remeshing needed
A
deformed mesh at true scale

The Material Point Method
5LAGRANGIAN EULERIAN
(A)
initial configuration
(B)
calculation step
(C)
after resetting the mesh
in each step :

The Material Point Method
6
initial position of
material points
final position of
material points
material points
move through
mesh
total displacements [m]total displacements [m]
collapsing soil column:
total displacements in [m]

7
Large deformation problems
dikes, dams, landslides
installation, impact
flowslides, erosion, liquefaction

8
Outline

9
Cutting forces in layered soils
Figure 1.1 Example of “Dry” chain cutter

10
underpressureincrease effective stresses
Water
inflow
shear
Volume increase due to dilation

11
• Problem
Trench depth’s of the order 6 meter. Hard clays &
variability in composition of soils in trenching for cables
and pipelines.
• Objective
cutting forces unknown in inhomogeneous soils consisting
of clays and sand.
• Approach
✓ laboratory cutting tests on layered clay and sand
✓ Numerical modelling

12
What if:
sand clayclayClay obstructs drainage path:
greater sand cutting force expected
• Problem
Trench depth’s of the order 6 meter. Hard clays &
variability in composition of soils in trenching for cables
and pipelines.
• Objective
cutting forces unknown in inhomogeneous soils consisting
of clays and sand.
• Approach
✓ laboratory cutting tests on layered clay and sand
✓ Numerical modelling

13
• Cutting blade moving
• through layer soils
rotated for
test and model
Linear vertical cut Linear horizontal cut
Chain cutter

14

15
Width of the blade is 0.25 m and the instrumented central part is 0.15 m wide

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CLAY CLAYSAND
• Significant variation in sand reaction forces
• Smoother pattern in clay

17

18
CLAY
SAND
8S4C 4S8C 20S32C
• Reaction force in clay is lower than the one of the homogeneous layer
• Reaction forces of the interlayered sand-clay system tends to be in between the
“homogeneous” clay and “homogeneous” sand

19
SAND
CLAY
CLAY
FIXEDMATERIAL
4 cm sand, 8 cm clay sequence
SAND
Close-up view
h=3cm

20
Close-up view
SAND
CLAY
CLAY

21
TX3
TX3
TX3

22
Sand permeability
Initialcondition
Max.porosity
K = 6.7 10-5m/s
K = 1.5 10-4m/s
Analysis no.
Dr
[%]
k
[m/s]
1 75 6.7 10-5
2 75 1.5 10-4
3 85 6.7 10-5
4 85 1.5 10-4
Bulk density ring

23
Suction [kPa]
v=2m/s
Dr=85% - k=1.5 10-4 m/s: Excess pore pressure

24
t = 0.01s
t = 0.02s
t = 0.03s
t = 0.05s
Suction [kPa]
Dr=85% - k=1.5 10-4 m/s: Excess pore pressure

25
Cutting forces in layered soils Dr=85% - k=1.5 10-4 m/s: void ratio
t = 0.01s
t = 0.02s
t = 0.03s
t = 0.05s
Void ratio [-]
0.8 1.0
1.10.7

26
t = 0.01s
t = 0.02s
k = 1.5 10-4 m/s k = 6.7 10-5 m/s
Suction [kPa]
Excess pore pressure: effect permeability

27
t = 0.01s
t = 0.02s
Dr = 85% Dr = 75%
Suction [kPa]
Excess pore pressure: effect Dr

28
v=2m/s
v = 2 m/s

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t = 0.01s
t = 0.02s
t = 0.03s
t = 0.05s
4 cm
8 cm
CLAY SAND
CLAY SAND

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• Reaction forces for 8S4C and 4S8C are bounded between Homogeneous Clay and Homogeneous Sand.
• 8cm are enough to reach the homogeneous conditions

31
t = 0.01s
t = 0.02s
t = 0.03s
t = 0.05s
Void ratio [-]
0.8 1.0
1.10.7

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• Reaction forces for 4S2C and 2S4C are again bounded between homogeneous sand
and homogeneous clay
2S4C
4S2C
v=2m/s

33
A.M. Talmon, M. Martinelli and H.J. Luger, 2019, Numerical simulation of cutting tests on layered sand and
clay, WODCON XXII, Shanghai, April 25-29.
NEW Possibilities in calculation for soil excavation!, reducing risks,
facilitating cutting deep trenches.
-Calculated shear planes in failure are not as clear cut as in observation-
based regime sketches and previous semi-analytical modelling.
-Similar time-series pattern in lab tests and MPM calculation.
-MPM: ~ weighed average of composited soil. Contrary to a bias to clay
domination in measurements.

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Outline

Monopiles
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Current monpile installation methods
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Jacking
Impact driving
Vibro-
driving
Fstat
Fdyn
Fstat
(displacement controlled)
Fstat
Grabe et al.

Requirements numerical analysis of installation process
• Large deformations
• Dynamic and cyclic loading under high frequencies
• Saturated sand (coupled-analysis)
• Generation and dissipation of excess pore water pressures
• Liquefaction along shaft for vibrated pile
• Sand is complex material with stiffness, strength, dilation
depending on density and stress
• Interaction between monopile and soil (SSI)
• Realistic computation times!
37

2D-Axisymmetry MPM
• 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
• The rest of formulation of 2D axisymmetric MPM is similar
to the 2D axisymmetric formulation of FEM
38
Galavi, V., Tehrani, F.S., Martinelli, M., Elkadi, A.S. & Luger, D. (2018).
Axisymmetric formulation of the material point method for geotechnical engineering applications.
9th European Conference on Numerical Methods in Geotechnical Engineering (NUMGE18)

Small scale monotonic/cyclic installation
39
Stoevelaaret al. (2011)
Baskarp sand is used
Acceleration = 80 g
Dimensions of the centrifuge set-up

40
Pile
Soil
~ 9000 linear triangle elements

41
~ 48000 material points

42
Dr = 38%

43
Dr = 66%

Small scale impact-driven installation
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• Dry sand
• Three different relative densities,
namely 40%, 60% and 90% (up to 3% error)
• Mass of hammer: 3 kg
• Fall height: 1 m
• Diameter of tank: 2 m; height: 1.6 m

45

46

Full scale impact-driven installation
• 7.8 m diameter monopile, 0.07 m wall-thickness
• Driven in the North Sea
• Total length of ~77 m, ~34 m in the sea bed.
• Water depth ~40 m
Data provided by Boskalis
• Soil layers:
• CPT values, relative density
• Type of hammer
• Geometry of pile
• Blow counts at different depths
47

• Soil: Double Hardening model
• Pile: Rigid
• 2-phase formulation
• (dynamic consolidation)
• Pile embedded initially at 4.7m
48
MovingmeshCompressingmesh
3.885 m

49
Vertical effective stress during Hammering Deviatoric strain during Hammering

0 50 100 150 200
5
6
7
8
9
10
11
12
Blow
Depth(m)
50
0 50 100 150 200 250
4
5
6
7
8
9
10
11
BlowDepth
------ 𝜓 = 4
------ 𝜓 = 1
------ 𝜓 = 0.5
Field Data o
------ Permeability =1e-3 m/s
------ Permeability =1e-4 m/s
Field Data o
0 50 100 150 200
5
6
7
8
9
10
11
12
Blow
Depth(m)

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Change in density in cross-section after
2 m penetration
Horizontal effective stresses after
lateral loading

Summary
• The material point method has been further developed, optimized, and successfully applied in
simulating the process of monopile installation for impact driving (field-scale monopile) and low
frequency vibratory driving (centrifuge scale)
• The solution is capable of coping with dynamic cyclic, coupled, large-deformation, soil-water-
structure interaction problems
52
V Galavi, FS Tehrani, M Martinelli, AS Elkadi, D Luger. Axisymmetric formulation of the material point method
for geotechnical engineering applications. Numerical Methods in Geotechnical Engineering IX, 427-434
Galavi V., Martinelli M., Ghasemi P., Elkadi A., Rene Thijssen R. - Numerical simulation of an impact driven
offshore monopile. Geotechnique 2019 (in preparation)

DSD-NL 2019 Anura3D ontwikkelingen - Analyse grote deformaties in de geotechniek - Martinelli

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