luger modeling soil-structure interaction
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Developments in modelling techniquesof soil-water-structure interaction
History, examples and practical applications
Dirk Luger
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Contents
Introduction and main messages
History and lessons learned as a journey through time
• Storm Surge Barrier “Maeslantkering” near Rotterdam (1995)
• Palm Deira earthquake deformations (2006)• Incheon bridge ship collision protection (2006)
• Earthquake amplification factors (2009)
• Windjack spudcan impact study (2012)
• Marsrover wheel-soil interaction (2013)
• Burgum bridge pier protection (2015)
Closure
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Introduction and main messages
• My background: more emphasis on predicting soil structure
behaviour as realistic as possible rather on calculations thataim to prove that a certain design code or standard is
complied with. That comes later.
• Another reason for that comes from my involvement in
forensic geotechnical engineering. That’s an area where
understanding what actually happened is crucial.
• This requires selection of parameters fit for the job. Purpose
of the calculation and the mechanisms that develop can
determine to a large extent what the proper set of soil
parameters is.
You will seldom get the proper soil parameters “of the
shelf”. You’ll have to make them consistent with your
engineering problem.
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Introduction and main messages
• A voyage through time to put what we can do nowadays into
perspective
• Quality and power of the tools at our disposal have increasedenormously
• With that the risk that calculation results are taken for granted
has increased as well (they look nice and “everything is
modeled, so it has to be OK…..)
You have to keep thinking, train your engineering
judgment and learn to trust it. Simple checks can
reveal a lot!
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Introduction and main messages
• When extrapolating beyond tested ranges or application areas
verification of our models by feedback from actual behaviour (monitoring structures) and from model tests is
indispensable.
• Whenever you’re venturing in an area where you haven’t been
before, make sure you’ve done everything to verify that yourcalculations are reliable.
Calculation Physical model Real Structure
Feedback loops
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Maeslantkering
Storm Surge Barrier
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Foundation block
North door
Dry dock
Main truss
Barrier sill
Control building
Ball joint
rimary sheet pile wall
Driving unit
Main components, North side
Sea
Rotterdam, river
Back-up sheet pile wall
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And actually, during a design meeting on site, in which some people
expressed their doubt regarding this risk we were suddenly warned
that a ship had collided with the main sheetpile wall, fortunately at a
moment and a place which did not lead to flooding of the building
pit…..
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Geotechnical design calculations
• ‘Traditional’ settlement calcs.(level of terrain, settlement of foundation block)
• 2-D FEM calculations(parallel to main loading direction, perpendicular to
sheetpile wall, before and after ship collision)
• BEM calculations(Stresses under foundation block)
• Discrete element dynamic calculations
(Ship collision effects)
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Asymmetric loading and combined perpendicular and in-
plane loading of the sheet pile wall, both through soil andvia anchors.
Having to account for
interaction between:
- Foundation block- Back-up sheetpile wall
- Main sheetpile wall
Interaction
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Parallel modeling (direction of main load)
Displacements
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Perpendicular modeling
Displacements
Loads from parallel
and perpendicularcalculations were
combined to determine
the final dimensions
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3-D BEM calculations(Stresses under foundation block)
+ =
+
=
Self-weight
Surrounding
ballast
Combination of both
0.2 MPa
0 MPa
-0.1 MPa
-0.1 MPa
0.3 MPa
0.2 MPa
0.1 MPa
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Construction of the dock at the South side
C t ti f th d i th d k
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Construction of the door in the dock
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The main truss
500 mm camber during supported construction80 mm camber after removal of supports
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and closed….
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Earthquake induced displacements
A method developed in the context of thePalm Deira development
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Seismic Risk 2008 26
Question
How to verify that my
embankment structureremains within acceptable
deformation limits if the
“design earthquake” occurs?
+0.6
+0.4
+0.2
0.0
-0.2
-0.4
-0.6
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Seismic Risk 2008 28
Sliding Block
Use published graphs or
perform own integration ofselected time-histories to
determine earthquake-
induced displacement.
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Seismic Risk 2008 29
Sliding block
PGA
Ayield
• Advantage:
Simple – easy to evaluate for many time histories• Disadvantage:
Only one displacement value (for the “sliding block”)
Not accounting for water next to the slope
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Seismic Risk 2008 30
Sliding block
PGA = 0.4 g
ay=0.2 g ay=0.1 gay=0.25 g
• Advantage:
Simple – easy to evaluate for many time histories• Disadvantage:
Only one displacement value (for the “sliding block”)
Not accounting for water next to the slope
Not accounting for failure in overlying layers
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Seismic Risk 2008 31
Dynamic FE analysis
Actual acceleration time history as
boundary condition at the base of
the mesh.
+ Continuous deformation field
- CPU intensive
- One time-history is not sufficient
- Free water causes problems
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Seismic Risk 2008 32
Deforming Continuum Method
Apply a constant horizontal acceleration at the base of the model
and observe what acceleration level can be transferred tothe different parts of the embankment
Each line represents 0.2 m/s2 = 0.02 g
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Seismic Risk 2008 33
Excess pore pressures
• Estimate on basis of ‘standard’ procedures: Cyclic shear stress level andrelative density of the soil.
• At the onset of the earthquake excess pore pressures a zero, by the end
they have reached their maximum value.
• Current approach: use the average…..
+0.6
+0.4
+0.2
0.0
-0.2
-0.4
-0.6
Entering excess pore pressures in
the model by reduction of the
material strength: at 50% excess
pore pressure we introduce a
material that has 50% of its original
strength:
Φnew = atan(0.5 tan(Φorg ))
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Seismic Risk 2008 34
Sample
Mesh
Hor. acceleration
Vert. acceleration
Shear strains
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Seismic Risk 2008 35
Accelerations and displacements
Ayield-vert [g]
Ayield-hor [g]
-0,12 ; -0,065
-0,11 ; -0,04 -0,07 ; -0,04
-0,04; -0,02
-0,035 ; -0,005
Verpl-vert [cm]
Verpl-hor [cm]
≈ 10 cm
≤ 1 cm
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Seismic Risk 2008 36
In short: A nice method filling “the gap”?
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Incheon Bridge Ship collision prevention
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Idealized prototype – 20 m diameter
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The dolphin model
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Modelling the sheetpile
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Set-up of the model
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sand filled
container
water basin
assembly plate
actuator dolphin
moving mass
mounting plate
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Set-up of the model
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After the test
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Forces derived from ship slowdown
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Earthquake amplification factors
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E th k lifi ti f t
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Earthquake amplification factors
Limits to PGA
and amplification
Li it t l ti li i l i
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Limit to acceleration - preliminary analysis
0 1,0 2,0 3,0 4,0 5,0-6,0
-4,0
-2,0
0,0
2,0
4,0
Dynamic time [s]
Acceleration
CP stand 0.5g...
Point A -394.4
Point B -397.1
Point C -399.7
Point D -401.5
Point E -404.7
Point F -410.6
Point G -427.0
Point H -441.7
Point I -456.7
Point J -464.0
Demonstrated mechanism but needed clearer presentation
M h i
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Mechanism
M1
Su1
M2
Su2
M3
| Peak acceleration | < Su1 / M1
So in the top layer 2 values
| Peak acceleration | < (Su1 ± Su2) / M2
So for an intermediate layer 4 values
T t f i l i l
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Try out for simple signal
Input at base 1g at 1Hz
V l iti k it l
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Velocities make it clear
0 1,0 2,0 3,0 4,0 5,0-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
2,0
Dynamic time [s]
Vx [m/s]
Time_vx
Point A
Point J
Point I
Point H
Point G
Point F
Point E
Point D
Point C
Point B
V l iti k it l
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Velocities make it clear
0 1,0 2,0 3,0 4,0 5,0-2,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
2,0
Dynamic time [s]
Vx [m/s]
Time_vx
Point A
Point J
Point I
Point H
Point G
Point F
Point E
Point D
Point C
Point B
Amplification at 1g base acc
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Amplification at 1g base acc.
Input at base 1g at 0.4 Hz
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WindJack
Spudcan-seabed impact interaction
The WindJack JIP
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06-Feb-14
The WindJack JIP
Soil-Structure Interaction Modelling 59
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 61
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 62
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 63
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 64
Forces have to be
corrected for inertia
effects.
Note the force to set
the spudcan in motion
and the force to stop it
again.
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 65
Initial analytical spudcan-
seabed interaction model
performance.
Still without hydro-
dynamic effects, inertia
and rate effects.
The WindJack JIP
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The WindJack JIP
Soil-Structure Interaction Modelling 66
The WindJack JIP
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The WindJack JIP
MPM calculation results
Soil-Structure Interaction Modelling 67
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Marsrover wheel-soil interaction
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Previous work: Discrete Element Method (DEM)
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Previous work: Discrete Element Method (DEM)
advantage: grousers possible, numerical stability
disadvantages:
• often 2D, unrealistic soil transport (impossible to go sideways)
• parameters for particles difficult to relate to physical quantities
• less suitable for compactive geomaterials (powder like)
70
Example of coupled Eulerian-Lagrangian FEM
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Example of coupled Eulerian Lagrangian FEM
Eulerian soil model and rigid (Lagrangian) wheel.
71
Wheel/soil is half because of symmetry
Flexible wheel modeling
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Flexible wheel modeling
Diameter 25 cm, width 11.2 cm.
grousersshell
Deformable
body
Only half of the wheel is
modeled (symmetry in FEM
model)
Rigid wheel modeling
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Rigid wheel modeling
Diameter 25 cm, width 11.2 cm.
Same features as flexwheel, in rigid body
constraint
Only half of the wheel is
modeled (symmetry in FEM
model)
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Rigid wheel 60% slip
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Burgum bridge pier protection
Analysis of bridge pier
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Analysis of bridge pier
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Little effect of meshing ……
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Little effect of meshing ……
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Soil parameters
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So pa a ete s
Dr γsat eini E50_ref Eoed_ref Eur_ref G0_ref γ0.7 φ Ψ(*)
% [kN/m3] [-] [kPa] [kPa] [kPa] [kPa] [%] [degr] [degr]
50 17.0 0.60 35000 35000 105000 94000 0.0150 34.3 4.3(2.15)
75 18.0 0.52 50000 50000 150000 111000 0.0125 37.4 7.4
(3.7)
65 17.6 0.55 44000 44000 132000 104200 0.0135 36.1 6.1(3.05)
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Parameters for larger strains
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g
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Interface strength @ sheetpiles
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g @ p
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a part where soil-soil or concrete-
concrete friction is mobilized anda strength reduction factor of 1.0
applies and
a part where soil-steel or
concrete-steel friction is
mobilized where typically a
strength reduction factor of 0.67is applied.
Rinter = (422/1160)*0.67 + ((1160-422)/1160)*1.0 = 0.88
Effect of lower dilatancy
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y
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Still room for optimisation: from 22m to 18m
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p
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Effect of the bridge
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g
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Movement of the bridge
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g
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Results
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Closure – main messages
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• Train your engineering judgment and learn to trust it.
Simple checks can reveal a lot!
• Select proper soil parameters, consistent with your
engineering problem.
• Verify models by feedback from actual behaviour
(monitoring of structures) and by performing modeltests.
Closure - thanks
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For further info on Deltares or this presentation feel free to contact:
In the Netherlands:Dirk Luger [email protected] M:+31 6 2049 1414
In Dubai:
Geoff Toms [email protected] M:+971 4 337 8353
mailto:[email protected]:[email protected]:[email protected]:[email protected]