Integrated Solver Optimized for the next generation 64-bit platform
Finite Element Solutions for Geotechnical Engineering
MIDAS Geotechnical Training SeriesFully Coupled vs Consolidation Analysis
MIDAS Information Technology
Seongwan Bae
Angel F. Martinez
Integrated Solver Optimized for the next generation 64-bit platform
Finite Element Solutions for Geotechnical Engineering
Project Overview
(Fully Coupled vs Consolidation Analysis)
GTS NX
3
Geometry Import
Geometry Works
Mesh generation
Boundary Conditions
Load Conditions
Define Water Level
STEP 01
STEP 02
STEP 03
STEP 04
STEP 05
STEP 06
Define Construction Sequence
Analysis Case
STEP 07
STEP 08
Perform analysis and check resultSTEP 09
Overview
GTS NX
Overview
1-4
01 Consolidation_by several methods
• In order to accelerate consolidation
without additional embankment and
potential shear failure of soil, a
uniform atmospheric pressure can be
applied to each depth of the soft
layer.
•This example is to compare the
results between Suction drain
method and Embankment with free
drainage by fully coupled and
consolidation methods
• Main objectives for this analysis are
as follows.
➢ Initial and long term settlements
during and after construction
➢ Compressibility
➢ Lateral ground flow
➢ Slope failure / reduction of bearing
capacity
➢ Differential settlement on adjacent
structures, services (road)
➢ Improvement methods – drainage,
solidification, compaction
GTS NX
1-5
02 Material for Soil and Structures
Name Embankment AS1 Ac AS2
Material Isotropic Isotropic Isotropic Isotropic
Model Type Elastic ElasticModified Cam
ClayElastic
General
Elastic Modulus (E) 10000 5000 3450 140000
Poisson’s Ratio(v) 0.33 0.33 0.35 0.33
Unit Weight(r) 17 18 16 19
Ko 0.5 0.5 0.5 0.5
Porous
Unit Weight(Saturated) 18 18 16 19
Initial Void Ratio(eo) 0 0 1.76 0
Permeability (kx,ky,kz) (m/day) 0.009 0.009 0.001 0.86
Non-Linear
OCR - - 2.05 -
Slope of Consol line (λ) - - 0.313 -
Slope of Over Consol Line (k) - - 0.063 -
Slope of critical State Line (M) - - 1.113 -
GTS NX
1-6
03 Soil Property (2D Plain Strain Element)
Name Embankment AS1 Ac AS2
Property 2D 2D 2D 2D
Model Type Plain Strain Plain Strain Plain Strain Plain Strain
Material Embankment AS1 Ac AS2
GTS NX
1-7
04 Construction Sequence (3 sets)
* Analysis Case 1 (Fully Coupled
Suction Drain)
1. Initial state of ground
2. Apply suction to each depth
at an interval of 5m (100
days)
3. Leave time (1000 days)
* Analysis Case 2 (Fully Coupled
Embankment)
1. Initial state of ground
2. Embankment (100 days)
3. Leave time (1000 days)
* Analysis Case 3 (Consolidation
Embankment )
1. Initial state of ground
2. Embankment (100 days)
3. Leave time (1000 days)
GTS NX
Stress→ Consider P.W.P for stress analysis
→ Time-Independent nonlinear static analysis
Drained: Long-term stability
Undrained: Short-term stability
Seepage
StressSeepage
Fully coupled analysis
→ Time-integrating method / Time-Dependent analysis
→ Changes in stress/stain/pore pressure with time
→ Governed by permeability of ground
[One way coupled]
[Two way coupled interaction]
Fully vs Semi Coupled Analysis
• Semi Coupled or Sequential analysis is the simplest way to consider the pore water pressure distribution by conducting seepage analysis beforehand, and reflecting it in the total stress/effective stress relationship equation of the stress analysis conducted in the following step. This method can be used to understand the static stress state of the given steady groundwater flow. However, since deformation due to stress analysis does not influence the seepage phenomenon inversely, there is no two-way coupling.
• Fully-coupled Stress-Seepage analysis is the two-way coupled analysis between seepage analysis and stress analysis. Both analyses are used to solve the coupled equation. It can display the pore water pressure, stress or deformation changes with time.
Semi coupled analysis
GTS NX
DOF for displacement and
excessive pore stress
Constant hydrostatic pressure
Simulate dissipation of excessive
p.w.p with time
Consolidation analysis
DOF for displacement and total
pore stress
Simulate changes in hydrostatic
pressure with time.
All seepage boundaries (head,
flux, review) are available.
Fully coupled analysis Fully coupled
Consolidation
<Difference>
<Common>
→ Two way coupled interaction
→ Time dependent behavior based on quasi-static analysis
Consolidation vs Fully Coupled
[Relation b/w two analyses]
• The consolidation analysis begins with the assumption that steady state pore water pressure can be maintained, and is used to see the changes in excess pore water pressure. In other words, this analysis is used to simulate the phenomenon of how excess pore water pressure changes with the changes in load/boundary conditions.
• Fully-coupled Stress-Seepage analysis does not follow assumption that steady state pore water pressure is maintained. Hence, it is suitable for simulating the transient seepage phenomenon, stress analysis and stability in abnormal condition in a fully coupledform. Unlike the consolidation analysis, it is possible to define the changes in seepage boundary conditions with time, boundary flow rate etc. In other words, for Fully-coupled Stress-Seepage analysis, it is possible to use all the transient seepage boundary conditions, structural load and boundary conditions.
GTS NX
1-10
GeneralWater Level
[Line(2D), Surface(3D)]
Water Level for Mesh Set
Seepage / Fully Coupled Analysis
Nodal Head
Nodal Flux
Surface Flux
Review
Consolidation Analysis
Draining Condition
Non Consolidation
Key Boundary Conditions
Used to simulate the domain where the excess pore pressure is 0 (drain). The Drainage condition is used as a boundary condition for Consolidation analysis.
The elements have an additional pore pressure degree of freedom, as well as displacement degree of freedom, at the nodes. Used to model non-consolidation layers to turn off PP degree of freedom.
Input the head of the model. Both the constant head value for steady state analysis and the changing head value for Transient analysis can be entered by applying the Seepage boundary condition function. The Nodal head is used as a boundary condition for Seepage/Consolidation analysis (Fully-Coupled).
Create a changing groundwater level by selecting a geometry shape on the work screen.
GTS NXConcepts of Coupled Analysis
Semi-Coupled Consolidation Fully-Coupled
Nodal head(total head) O X O
Nodal head(pressure head) O X O
Boundary review O X O
Drainage condition X OO
(total head=0)
Non-consolidated condition X O O
Node/surface flow O X O
<List of applicable load/boundary conditions for each coupled analysis type>
< Outline of coupled analysis>
Fully Drained
Integrated Solver Optimized for the next generation 64-bit platform
Finite Element Solutions for Geotechnical Engineering
Modeling Procedure
(Fully Coupled vs Consolidation Analysis)
GTS NX
Procedure
1-13
01 Create New Project
11
Main Menu > New
Analysis Setting > Model Type >
2D
Unit System > kN-m-day
2
2
GTS NX
Procedure
1-14
02
1
1
Main Menu > Import > DXF 2D
(Wireframe)
Select AutoCAD DXF File >
Embankment Consolidation vs
Fully Coupled CAD.dxf Open
Select OK
2
2
3
3
3
Geometry works (Create or Import from AutoCAD)
GTS NX
Procedure
1-15
03 Define Material / Property for Soil & Structures
1 Mesh > Prop. > Property >
Import
Select “Embankment
Consolidation vs Fully Coupled
Final.gts” file
Select All
Select OK
* Can Import from the existing model
file (Refer to Project Overview >
Material / Property)
2
3
1
2
3
1
GTS NX
Procedure
1-16
04 Generate Mesh (2D Element)
1 Mesh > Generate > 2D > Auto -
Area
Select Edge(s) > Select edges
for “Embankment” as
highlighted in the figure.
Input element Size : 1
(1m between two nodes)
Select Property : Embankment
Input Mesh Set Name :
Embankment
Select Apply
(Follow the same procedure
for below soil layers)
2
2
2
3
4
5
3
4
5
It is possible to input different size of element for each area. All nodes at each boundary line
will be connected automatically. This is to control Mesh Quality and the number of elements.
6
6
1
GTS NX
Procedure
1-17
04 Generate Mesh (2D Element)
1 Mesh > Generate > 2D > Auto -
Area
Select Edge(s) > Select edges
for “AS1” as highlighted in the
figure.
Input element Size : 1
(1m between two nodes)
Select Property : AS1
Input Mesh Set Name : AS1
Select Apply
(Follow the same procedure
for below soil layers)
2
2
2
3
4
5
3
4
5
6
6
After creating mesh for all area at once, it is possible to change “Property”.
Go to “Mesh > Element > Parameters > 2D”
1
GTS NX
Procedure
1-18
05 Define Boundary Condition (Water Level)
1 Static / Slope Analysis >
Boundary > Water Level > Edge
Select Target Edge(s) > Select
edges to define water level as
highlighted in the figure.
Interval : 1 (m)
Input Name : Water Level (1)
Select OK
1* 1 Water Level Function will be
defined for initial water level.
In the works tree, there are 1
water level functions created
automatically.
2
3
4
5
2
3
4
5
Initial Water Level
GTS NX
Procedure
1-19
05 Define Boundary Condition (Ground)
1 Seepage/Consolidation
Analysis > Boundary >
Constraint > Auto
Boundary Set Name : Ground
Boundary
2
2
1
GTS NX
Procedure
1-20
05 Define Boundary Condition (Suction Drain)
1 Seepage/Consolidation
Analysis > Boundary > Nodal
Head
Select Object(s) > Select 9 edges
for “Suction drain” as
highlighted in the figure.
Value : -5
Select Type : Pressure
Boundary Set Name : Suction
1
2
2
3
4
5
3
4
5
Practical suction pressure is within
the range of 50~100kPa,
depending on the field condition.
-5 = -5 x 9.8kN/m2 = 49kPa
GTS NX
Procedure
1-21
05 Define Boundary Condition (Drain by Total Head)
1 Seepage/Consolidation
Analysis > Boundary > Total
Head
Select Object(s) > Select 10
edges as shown
Value 2m Pressure
Boundary Set Name Draining
Total Head
Repeat for bottom layer with
12m Pressure
1
2
2
3
4
3
4
Pore pressure set to given values
5
5
GTS NX
Procedure
1-22
05 Define Boundary Condition (Consolidation)
1 Seepage/Consolidation
Analysis > Boundary > Draining
Condition
Type Edge
Select Object(s) > Select 20
edges as shown
Boundary Set Name Draining
Condition
1
2
2
3
4
3
4 Pore pressure goes to 0 on
selected nodes.
GTS NX
Procedure
1-23
05 Define Boundary Condition (Consolidation)
1 Seepage/Consolidation
Analysis > Boundary > Non
Consolidation
Type Element
Select Embankment
Boundary Set Non Consolidation
1
2
2
3
4
3
4 Pore pressure degree of freedom
turned off.
GTS NX
Procedure
1-24
06 Load Condition (Self Weight)
1
1 Seepage/Consolidation
Analysis > Load > Self Weight
Load Set Name : S/W2
2
GTS NX
Procedure
1-25
07 Define Construction Stage (Create 2 Stage Set)
1Seepage/Consolidation
Analysis > Construction Stage >
Stage Set
Stage Type > Consolidation
Set Name : Consolidation
Embankment
Select Add
Stage Type > Fully Coupled
Stress Seepage
Set Name : Suction Drain
Select Add
Repeat for Fully Coupled
Embankment Set
Select Suction Set and Click
Define CS…
* 3 Construction stage will be defined
for each stage set.
1
2
4
7
8
3
4
2
3
5
6
5
6
7
8
9
9
GTS NX
Procedure
1-26
08-1 Define Construction Stage (Suction Drain)
1 Stage 1 : Initial state
Time Step : Initial value (1)
Activated Data : Mesh Sets for
initial state of ground (2D
elements only except
“Embankment”), Ground
Boundary, Self Weight
Check “Define Water Level for
Global”
Input 1m, Select “Water Level
(1)”
Check “Clear Displacement”
Select Save
Select New
3
1
2
3
4
4
Drag & Drop
5
5
6
7
7
2
6
2
GTS NX
Procedure
1-27
1 Stage 2 : Suction
Time Step : 100 days / 10 steps
Activated Data : Suction
Select Save
Select New
3
1
2
3
4
Drag & Drop
5
5
2
4
2
08-1 Define Construction Stage (Suction Drain)
GTS NX
Procedure
1-28
1 Stage 3 : Leave Time
Time Step : 1000 days / 10 steps
Deactivated Data : Suction
Select Save
Select Close
*Create other 2 sets by
same procedure or by
making copies of sets and
modifying boundaries
applied.
2
3
4
2
1
4
2
5
Drag & Drop
5
3
08-1 Define Construction Stage (Suction Drain)
GTS NX
Procedure
1-29
08-2 Define Construction Stage (Embankment)
1 Stage 1 : Initial state
Time Step : Initial value (1)
Activated Data : Mesh Sets for
initial state of ground (2D
elements only except
“Embankment”), Ground
Boundary, Self Weight
Check “Define Water Level for
Global”
Input 1m, Select “Water Level
(1)”
Check “Clear Displacement”
Select Save
Select New
3
1
2
3
4
4
Drag & Drop
5
5
6
7
7
2
6
2
GTS NX
Procedure
1-30
1 Stage 2 : Embankment
Time Step : 100 days / 10 steps
Activated Data : Embankment
And Draining Total Head
Select Save
Select New
3
1
2
3
4
Drag & Drop
5
5
2
4
2
08-2 Define Construction Stage (Embankment)
GTS NX
Procedure
1-31
1 Stage 3 : Leave Time
Time Step : 1000 days / 10 steps
Select Save
Select Close
2
3
4
2
1
2
3 4
08-2 Define Construction Stage (Embankment)
GTS NX
Procedure
1-32
08-3 Define Construction Stage (Consolidation)
1 Stage 1 : Initial state
Time Step : Initial value (1)
Activated Data : Mesh Sets for
initial state of ground (2D
elements only except
“Embankment”), Ground
Boundary, Self Weight
Check “Define Water Level for
Global”
Input 1m, Select “Water Level
(1)”
Check “Clear Displacement”
Select Save
Select New
3
1
2
3
4
4
Drag & Drop
5
5
6
7
7
2
6
2
GTS NX
Procedure
1-33
1 Stage 2 : Embankment
Time Step : 100 days / 10 steps
Activated Data : Embankment,
Drainage Condition and Non-
Consolidation
Select Save
Select New
3
1
2
3
4
Drag & Drop5
5
2
4
2
08-3 Define Construction Stage (Consolidation)
GTS NX
Procedure
1-34
1 Stage 3 : Leave Time
Time Step : 1000 days / 10 steps
Select Save
Select Close
2
3
4
2
1
2
3 4
08-3 Define Construction Stage (Consolidation)
GTS NX
Procedure
1-35
09 Analysis Case
1
Analysis > Analysis Case >
General
Title : Case Name
Solution Type : Construction
Stage
Select Construction Stage Set :
Suction Drain
Analysis Control : Check each
option in Red Box
Select OK
Select OK
(Create 2nd and 3rd Analysis case
for Embankment stage by fully
coupled method and
consolidation method set with the
same options.
1
2
3
4
5
2
3
4
5
6
7
7
5
5
6
GTS NX
▪ Analysis > Analysis Case > General > Analysis Control
▪ Consider geometric nonlinear effects in stress, fully coupled and slope stability analysis.
▪ Analysis can take into account load nonlinearity. Reflecting the effects of follower loads, where the load direction changes with the deformation.
▪ In case of large deformation analysis, the user can check more reasonable behavior.
▪ In case of embankment, “Initial Configuration” option in General tab is applicable to check more realistic behavior.
Normal pressure Pressure in specified direction
[Directional change of pressure load due to the large deformation]
[Staged Consolidation analysis for embankment]
[Geometric nonlinearity + Initial configuration option]
[Linear geometry without option][Result comparison]
09 Review of Analysis Control (Geometric Nonlinearity)
GTS NX
Procedure
1-37
10 Perform Analysis and Check Results
1 Analysis > Analysis > Perform
Select OK
1
2
2
GTS NX
Procedure
1-38
11 Post Processing (Settlement with time)
1
Consolidation method.
From the RESULTS WORK TREE
Check Pore Pressure Head for
the last step in LEAVE TIME for
each of the analysis cases.
Fully Coupled Suction
Fully Coupled Embankment
GTS NX
Procedure
1-39
11 Post Processing (Settlement with time)
1 From the RESULTS WORK TREE
Check Total Displacements for
the last step in LEAVE TIME for
each of the analysis cases.
2
Consolidation method.
Fully Coupled Suction
Fully Coupled Embankment
GTS NX
Procedure
1-40
11 Post Processing (Settlement with time)
1 Result > Advanced > Extract
Select Analysis Set : Suction
Drain
Select Result Type :
Displacements
Select Results : TY
TRANSLATION(V) (vertical
displacement)
Select Nodal Results Extraction
Select Table
Select Two Column Export to
Excel
Repeat process for other cases
and graph settlement
comparison
1
2
3
4
5
6
2
3
4
3
5
6
6
GTS NX
1-41
- Suction drain: -50 kPa (60days)
[Pore pressure distribution with suction drain] Stage 2 (Embankment step 1)
<Fully Coupled Suction drain>
Results Comparison
<Consolidation>
[Excess Pore Pressure distribution with suction drain] Stage 2 (Embankment step 1)
-0.6
-0.4
-0.2
0.0
0 50 100 150 200 250 300
Max displacement
Suction drain period
[Maximum displacement vs. time]
Suction drain removed
Residual displacement
[Excess Pore Pressure vs Time
GTS NX
1-42
<Excavation - dewatering>
- Comparison of sequential and fully-coupled analysis
[Full Coupled Vertical displacement after 22 days]
Initial water level
layer1
layer2
Fully vs Semi Coupled Analysis
[Semi Coupled Vertical displacement after 22 days]
GTS NX
1-43
<Excavation - dewatering>
- Comparison of sequential and fully-coupled analysis
[Full Coupled Pore Pressure Head after 22 days]
Fully vs Semi Coupled Analysis
[Semi Coupled Pore Pressure Head after 22 days]
-6
-5
-4
-3
-2
-1
0
-1 1 3 5 7 9 11 13 15
Pre
ssure
Head
Time (day)
Pore Pressure vs Time
Integrated Solver Optimized for the next generation 64-bit platform
Finite Element Solutions for Geotechnical Engineering
END