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midas GTS Tutorial
Perform Semi-Coupled analysis to simulate dewatering + video
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1. Basic concept: Semi-coupled analysis
Model Overview
Model overview
A simple 2D model, as shown on the right,
is used to demonstrate the basic concept
behind semi-coupled analysis.
Nodal head is position dependent on the
location of the ground surface‟s global
coordinate system.
Total depth: 100m
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1. Basic concept: Semi-coupled analysis
Construction Stages 1st Construction Stage:
Define: Seepage analysis
2nd Construction Stage:
Define: Construction stage (stress analysis)
1st Construction Stage 2nd Construction Stage
BC: Boundary Condition
Sw: Self-weight
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1. Results
After running the analysis, two sets of results will be outputted to the post-works tree menu:
Seepage Analysis FIRST and Stress Analysis SECOND. The solver calculates the pore pressure
in stage one, then the results are carried over to stage two.
Stage one: Pore Pressure kN/m2 Stage two: Pore Pressure kN/m2
Note: Result settings for averaged or exact can be modified in Analysis > General Analysis Control
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2. Model: Nodal Head
Model > Boundary > Nodal Head 1) Location of Ground surface GCS (0,0,0)
2) Total head = 0 m
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• Drawdown levels:
a) -1.5m
b) -3m
c) -4.75m
d) -6.5m
e) -8.25m
f) -10m
g) -10.6m
1. Model: Nodal Head
c
d
e
f
g
b
a
Excavation layers
Model > Boundary > Nodal Head
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2. Model: Seepage Face
Model > Boundary > Seepage Face
• Using the suggested selection method, the four
inner walls of the ground to model the review
boundary condition.
Top view
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2. Model: Seepage Face
Model > Boundary > Seepage Face
• Using the suggested selection method, select top view
and select the element faces as shown in Figure 1.
Figure 1: Mid soil top view
Figure 2: Mid soil rotated bottom view
Figure 3: Mid soil rotated bottom view
with selection box
•Choose Deselect icon and create selection box as
shown in Figure 3. While holding the mouse button,
press „ctrl‟ button to turn the selection box from a
solid line to a perforated line. This will create an
absolute selection tool.
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Heaving can be identified in the output
window when a particular stage starts
to diverge.
2. Model: Boundary Conditions
Model > Boundary > Nodal Head
Figure 4: Heaving after removal of Excav#2
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By importing the results into the post-works tree, and activating the deformed shape option,
the heaving phenomenon can be identified visually. In this model, dewatering introduced heaving
at the bottom of Excav#2 and dredge layers. To mitigate the heaving effects,
Uz must be constrained.
2. Model: Boundary Conditions
Model > Boundary > Nodal Head
Figure 5: Heaving after removal of Excav#2Figure 6: Applying two boundary conditions to
control heave
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3. Construction Stages
Seepage analysis must be carried out first prior stress analysis to consider the coupling effects.
To consider a seepage analysis case, click “Insert” in the first initialization stage. This will
automatically insert a new stage before the initial stress stage. Click “New” to create a new stage
after a stress stage.
Model > Construction Stages > Define Construction Stages
New Seepage Analysis Case 2nd Stage Seepage Analysis Case
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3. Construction Stages
Model > Construction Stages > Define Construction Stages
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3. Construction Stages
Model > Construction Stages > Define Construction Stages
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3. Construction Stages
Model > Construction Stages > Define Construction Stages
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3. Construction Stages
Model > Construction Stages > Define Construction Stages
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Pore Pressure from Seepage Analysis
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Total Head Draw down levels from Seepage Analysis
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Pore Pressure after raft construction using quarter clipping view Iso Surface of pore pressure = 0 m at dredge
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Effective Stress Z‟ construction using quarter clipping view
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Total Stress Z construction using quarter clipping view
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