(GTS Demo)Dewatering

midas GTS 3D Tutorial

1 http://eng.midasuser.com/

midas GTS Tutorial

Perform Semi-Coupled analysis to simulate dewatering + video



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



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



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



2. Model: Nodal Head

Model > Boundary > Nodal Head 1) Location of Ground surface GCS (0,0,0)

2) Total head = 0 m



• 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



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



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.



Heaving can be identified in the output

window when a particular stage starts

to diverge.

2. Model: Boundary Conditions


Figure 4: Heaving after removal of Excav#2



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


Figure 5: Heaving after removal of Excav#2Figure 6: Applying two boundary conditions to

control heave



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



Pore Pressure from Seepage Analysis



Total Head Draw down levels from Seepage Analysis



Pore Pressure after raft construction using quarter clipping view Iso Surface of pore pressure = 0 m at dredge



Effective Stress Z‟ construction using quarter clipping view



Total Stress Z construction using quarter clipping view

(GTS Demo)Dewatering

Documents

Transcript of (GTS Demo)Dewatering