diamond engineer: tunnel series training 1northamerica.midasuser.com/web/upload/sample/...behavior...

Angel Francisco MartinezApplication Engineer

MIDAS NY

Diamond Engineer: Tunnel Series

Training 1

01 Introduction

02 Pre -Processing

03 Demo

Content

Introduction

No. 1 in software for civil engineering

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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]


Geometry

• 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


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.


Modeling

Modeling

• Divide Solid by surfaces• Delete Extra Solid on top


Modeling

• Draw Rectangle Surface in front of tunnel face• Make 3 copies in Y direction at 50m


Modeling

• Divide Tunnel Solid by surfaces• Divide touching surface of solid ground


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


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


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]


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


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


Stage 3 Excavation Stage 4: Final Excavation

Tunnel Moments Axial Forces in Rock Bolts

Bridge Axial Forces Bridge Moments


• 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

Thanks!http://globalsupport.midasuser.com/helpdesk/

diamond engineer: tunnel series training 1northamerica.midasuser.com/web/upload/sample/...behavior...

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