Angel Francisco MartinezApplication Engineer
MIDAS NY
Diamond Engineer: Tunnel Series
Training 1
01 Introduction
02 Pre -Processing
03 Demo
Content
Introduction
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About MIDAS
1-5
What are a Tunnel's Design Considerations
• Tunnel type / shape
• Construction sequence / Excavation methods
• Water level / hydraulic conditions
• Support system / ground improvements
• Ground status (soft soil, rock quality)
• Earth pressure coefficient (Ko)
• Adjacent services and structures
• etc.. (uncertainties)
Introduction
How do engineers design the tunnels?• Hand Calculations
• Structural software (1D)- Based on loads only - Lining Shape and thickness
• Geotech software (2D & 3D)- Fully considers ground- Excavation pattern and method
Introduction
What are the main tunnel excavation methods?
• Open Cut and Cover MethodCut and cover is the cheapest way to build a subway, but it has a
number of shortcomings.
It's very disruptive to local traffic, it requires that the subway to
be close to surface (<12m).
• Sequential Excavation Method (NATM)Tunnel face excavated in stages. Support element installed in between excavations stages. Uses shotcrete and interlocking frames.Slower than TBM for long tunnels but more economical.
• TBM (Tunnel Boring Machine)Excavation done by special machine that digs tube-like passage. Machine digs and installs support autoGood for long tunnels but very capital intensive.
Tunnel projects usually have a combination on methods
Introduction
1-8
Numerical modeling permits the analysis of complex tunnel excavation in sequences by
representing material constitutive behaviors, accurate structural geometries, realistic boundary conditions/loads, soil-structure interaction and critical processes such as consolidation and seepage. Ground displacements associated with tunnel
excavations occur in vector directions X-Y-Z, thus to accurately represent ground behavior during tunnel excavation processes, detailed 3D numerical analysis is vital.
Midas GTS-NX is a fully-integrated numerical modelling software for 3D FEM analysis.
WHY model Tunnels in 3D FEM?
Modeling tunnels in 3D is becoming more attractive because of
limitations of the 2D modeling and because it captures the response of tunnel excavations more accurately.
Any type of tunnel can be designed in 3D FEM
Introduction
1-10
Define analysis conditions and
run the high performance analysis
자동요소망생성
Modeling Analysis section
Automatic generation of shared
surfaces function
Check shared surfaces
Hybrid Mesh generationCheck results
Work flow for FEM analysis
[Import or automatically generate 3D
layers through actual field data]
Pre-Processing
Modeling
Key factors in numerical analysis
Geometry
• Simplified version of actual field conditions. Model only essential components.
• Complex geometry that cannot be simplified by 2-dimensional, symmetric conditions
• What a geometry model should represent?
o Ground layers, topographic surface (if non-horizontal)
o Solids, surfaces and lines to model ground and structural components such as soil volumes,
walls, props etc. for construction stages
Geometric Idealisation
Yes
Plane Strain
Axisymmetry
No3D
GeometryExcavation with underground structures
Intuitive User Interface makes it easy to Navigate
Commands based on AutoCADWork treeMessage window2D and 3D Analysis Setting
Modeling
Simplified ModelingAutoCAD geometries ImportPolylines onlyCenter near (0,0,0)
Importing
Importing
1-17
[Create ground surface using topographic map]
[Automatically generate 3D
geological stratum through
actual field data]
Key factors in numerical analysis
Geometry
1-18
• Grid Points Surface Import (50 ,50) (-1,-1) (LX 202, LY 202)• Draw Box at (0,0,-20) X:200m Y:200m H:220m• olids ShapesSweep• Intersect
CAD Commands for easy 3D modeling
Modeling
• Draw a wire type tunnel section on the ZX workplane at (100, 20). • R1:15m A1:60deg R2:10m A2:55deg• Include Rock Bolts #:11 Length:7m Tangential Pitch:5m
CAD Commands for easy 3D modeling
Modeling
• Draw a wire type tunnel section on the workplane.• Extrude 200m in Y to make 3D solid from 2D wire.• Copy rockbolts 10 times at 20m in Y direction.
CAD Commands for easy 3D modeling
Modeling
Modeling
• Divide Solid by surfaces• Delete Extra Solid on top
CAD Commands for easy 3D modeling
Modeling
• Draw Rectangle Surface in front of tunnel face• Make 3 copies in Y direction at 50m
CAD Commands for easy 3D modeling
Modeling
• Divide Tunnel Solid by surfaces• Divide touching surface of solid ground
CAD Commands for easy 3D modeling
Simplified ModelingVerification of Geometry connectionAuto Connect
Check Shapes
Check for shared faces after creating a 3D geometry object. Creating a mesh on an unshared solid created a free face makes obtaining accurate analysis results difficult. Such shared faces can be checked using Check Shape > Check Duplicates.
Meshing
1-27
Key factors in numerical analysis
Constitutive models
• Constitutive model relates incremental stress (∆σ) to strains (∆ε) with a stiffness matrix
representing stiffness of soil and structural elements
• Expressed either in terms of total stress or effective stress and pore pressure
• Soil and rock behaviour – linear elastic, nonlinear elastic, elasto-plastic, creep,
isotropic/anisotropic strength/stiffness
• Permeability parameters, Soil-water content curves for unsaturated soil
Constitutive Model Analysis Verify
Field
Measurement
Back Analysis
“Physical characteristics for soil to reproduce of ground behavior mathematically”
ε
σ
Elasto-Plastic
Hardening
Softening
Constitutive Models Data Base
Meshing
1-29
1D
Geogrid(1D)
Truss
Embedded truss
Beam
Pile
2D
Geogrid(2D)
Gauging shell
Shell (Plates)
Plane stress
Plane strain
3D
Solid
Applicable
Rigid link
Pile tip
User specified behavior
for Shell interface
Point spring
Matrix spring
Interface (Permeability)
Shell interface
Elastic link
Key factors in numerical analysis
Element Library
Structural data base
•Extraction of 2D and 1D elements to model reinforcement as a shotcrete and rock bolts
Rock Bolts ShotcreteTunnel walls Anchors
Meshing
• Finite Element Mesh – Unstructured (Automatic) & Structured (Mapped)
• For more accurate prediction of results in 3D analysis, use hexahedral element
dominated mesh
Auto Mesh Map Mesh
HexahedralTetrahedral Hybrid [Hexa dominated mesh]
Key factors in numerical analysis
Mesh (Elements)
Good for displacement Good for stress as well
Hexa elem.
Pyramid elem.
(connect hexa and tetra)
Tetra elem.
• Mesh size control
Meshing
Specify the size of elements surrounding the selected point. Select edges (lines) and use the following 5 methods to preset the position (mesh size) of the new mesh node. The node spacing can be directly entered or a selected line can be divided into constant or linearly changing segments.
1-33
Support multi-thread
during mesh generation
Meshing
• Parallel mesh 3D solids or mesh in stages.
• Size 8m tetra
Extract tunnel linings
34
1. Mesh > Element > Extract
2. Select Tunnel Excavation geometries to extract faces
Meshing
Rock Bolts
35
1. Mesh > Generate > 1D Element > 3 divisions2. Select all rock bolts3. Delete 1st and last set
Meshing
Tunnel Lining
•Extraction of 2D and 1D elements to model reinforcement as a shotcrete and rock bolts
Shotcrete as 2DTunnel lining with bolts
Properties
Advanced Meshing• Integrations of embedded structural elements and
connected with mesh• Check Mesh
Meshing
Interface Faults
GTS NX also allows you to model rock faults
using an interface.
A plane of the surface is used to model the
discontinuity.
Meshing
Analysis Set Up
1-40
General
Supports /(Auto, Manual)
Change Material Property
Beam End Release
Shell End Release
Water Level
[Line(2D), Surface(3D)]
Water Level for Mesh Set
Seepage / Fully Coupled Analysis
Nodal Head
Nodal Flux
Surface Flux
Review (Potential Seepage Review)
Dynamic Analysis
Transmitting Boundary
Elastic / Viscous Boundary
Boundary conditions
Water Level
Auto Constraints
Excavate > Install > Reinforce > Excavate
Initial stage (Intact Rock)Initial Rock Excavation Stages (Shield advances)
Tunnel Segment installation stages Grout Injection Stages
1-42
Static Loads
Self weight
Force
Moment
Displacement
Pressure
Water pressure
Line beam load
Element beam load
Temperature
Prestress
Initial equilibrium force
Combined load
Dynamic Loads
Response spectrum
Ground acceleration
Time varying static
Dynamic nodal
Dynamic surface
Load to Mass
Train Dynamic Load Table
Axial / Beam Loads
Load assignment reflecting field conditions
Initial Equilibrium Force
Pressure Loads
Water Pressure Loads
Self Weight
1-43
Analysis Cases
1-44
Analysis Case
Key factors in numerical analysis
Initial ground conditions (Water level)
Analysis Control Options
‘Auto Consider Water Pressure’ checked in
analysis control
(consider water pressure automatically on
excavation line/surface)
Axial force result
Analysis type considering water level
- Linear, Nonlinear, Eigenvalues, Time history analysis, etc.
- 3D water level, Partial saturation property, Negative pore
pressure
- Soil density with degree of saturation
Auto water pressure
(1 )e unsat e satS S
1-46
Static Results for ground and support structures
Slope stability analysis using SRM Strength
Reduction Method
3D slope model
Maximum shear strain
2D slope analysis result 1
2D slope analysis result 2
2D, 3D safety factors using SRM (Strength Reduction Method) for assessing slope stability
Slope failure during excavations
Ground dynamic analysis – Seismic analysis
(Liquefaction analysis, Effective stress analysis)
Analysis Model 1 Degree of Shear Stress
Deformation due to max. shear
Section Force of Structure
Analysis Model 2 Total Displacement Deformation due to max. shear
• Finitude of ground by using transmission
boundary
• Nonlinear shape of ground as linear
• Applicable to various subsurface structures
(tunnels, water and sewage, subway stations)
Complex Response Analysis: frequency region method for seismic analysis considering the interaction of structure and ground
Ground Vibration Evaluation due to moving load
Analysis Model 1 Analysis Results
Analysis Model 2 Vertical direction ground displacement
50
단 단 : m
단 단 단 단 (Viscous Boundary)
4단 단 단 단 단
83.5
Analysis for train and vehicle moving load conditions
Construction stage analysis
Section
Construction Stages
Stage1 Original ground
Stage2 Excavation
Stage3 SIG placing
Stage4 Box Construction
Stage5 Banking
Stage6 Additional Load
Analysis Results
Y-dir. Displacement diagram
Failure Diagram
Vertical Stress Diagram
Axial Force Diagram
3D Analysis considering construction stages when constructing Open Cut Tunnel
Stability during construction stages applying SIG placing method for reviewing the appropriateness and stability of foundation
Construction stage analysis
Effects on Bridge from Tunnel Excavation
Initial Stage Stage 2 Excavation
Effects on Bridge from Tunnel Excavation
Stage 3 Excavation Stage 4: Final Excavation
Tunnel Moments Axial Forces in Rock Bolts
Bridge Axial Forces Bridge Moments
Effects on Bridge from Tunnel Excavation
• Conventional methods are practical for basic cases but have many limitations.
• 2D is advantageous when terrain is simple and tunnel segment is straight only.
• The 3D FEM allows for accurate simulation of terrain and sequential construction
process.
• It is important to compare and calibrate advanced 3D models based on
conventional methods.
Conclusions
Assignment
1D Tunnel Lining
Open 2D Start File or Input materials
1-58
Step 1:Draw
Geometry
Step 2:Mesh Lining
Step 3:Apply Load
Step 4:Apply
Boundary Conditions
Step 5:Review Results
Run Analysis
1D Tunnel Lining
Step 1:Draw Geometry
1D Tunnel Lining
Step 2:Mesh Lining
1D Tunnel Lining
Step 3:Apply Load
Select nodes in order as shownApply load in Global Xw1 = 83.325 kN/mw2 = 30 kN/m
Select nodes in order as shownApply load in Global Xw1 = -83.325 kN/mw2 = -30 kN/m
1D Tunnel Lining
Step 3:Apply Load
Select nodes in order as shownApply load in Global Yw1 = -136.65 kN/mw2 = -60 kN/m
1D Tunnel Lining
Step 4:Apply Boundary Conditions
• CREATE > OTHER > Surface Spring• Select nodes on the base as
shown• Elastic Spring• GCS-Y• Modulus of subgrade reaction:
31616 kN/m
1D Tunnel Lining
Step 5:Run Analysis
1D Tunnel Lining
Review Results: Post Processor
Training 2:
Post Processor & Wizards
http://northamerica.midasuser.com
Send model to: [email protected]
1D Tunnel Lining
Integrated Solver Optimized for the next generation 64-bit platform
Finite Element Solutions for Geotechnical Engineering
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