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Reinforced Earth

Buried Arch StructuresIEAust March 1998

TechSpan Arch Structures

Prediction, Performance and

Projects

Doug Jenkins

Engineering Manager 

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Overview

History of the arch

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Reinforced Earth introduced TechSpan in 1986

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Overview

What is TechSpan?

What is new about it?

What is clever about it?

Why finite element analysis?

Does it work? What does it mean for the client?

Groupe TAI

The Reinforced Earth Company

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Overview

Analysis of buried arch structures

 – Methods of Analysis

 – Factors affecting the accuracy of results

Prediction Versus Performance

 – Site measurements at the Oita TechSpan

 – Comparison of site measurements and analysis

results

 – Summary

 – Conclusions

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The Reinforced Earth Company

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Overview

Projects

 – Homebush Bay Rail Link 

 – Olympic Park TechSpan; Melbourne City Link 

Project

 – Queensland Mine, River Crossing;

5500 Tonne live load – Olympic Dam Load Out Tunnel

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The Reinforced Earth Company

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ROAD 

RAILWAY 

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The Reinforced Earth Company

RIVER CROSSING 

MINE 

Th R i f d E th C

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Typical TechSpan Cross SectionGroupe TAI

The Reinforced Earth Company

Th R i f d E th C

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Analysis of buried arch structures

Methods of Analysis

 – Simple elastic analysis

All materials properties linear elastic

Vertical soil pressure assumed proportional to depth

Horizontal soil pressure = constant x vertical

 pressure

Horizontal pressure may take different value on

each side

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The Reinforced Earth Company

Th R i f d E th C

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The Reinforced Earth Company

Th R i f d E th C

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Analysis of buried arch structures 

Methods of Analysis

 – Beam and spring model

All materials properties linear elastic

Vertical soil pressure assumed proportional to depth

Horizontal soil pressure = constant x vertical

 pressure

Soil structure interaction modeled by compression

only elastic springs

Construction sequence modeled in the analysis,

excluding compaction loading

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The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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Analysis of buried arch structures

Methods of Analysis

 – Finite Element Analysis

Elasto-plastic soil properties with varying elasticmodulus (“Duncan model”); concrete linear elastic 

Vertical and horizontal soil pressure and soil

structure interaction determined by finite element

analysis Construction sequence modeled in the analysis,

including compaction loading

Friction elements to allow slip between soil and arch

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The Reinforced Earth Company

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Typical TechSpan Finite Element Mesh

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Factors Affecting the Accuracy

of Results Soil stress-strain behaviour 

 –  Non linear 

 – Failure stress and initial elastic modulusaffected by confining pressure

 – Loading and unloading behaviour different

Soil structure interaction – Construction sequence

 – Locked in stresses

 – Soil arching

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The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

The Reinforced Earth Company

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The Reinforced Earth Company

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p y

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p y

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p y

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p y

The Reinforced Earth Company

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Site Measurements at Oita

Deflection measurements

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The Reinforced Earth Company

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Oita TechSpan, Deflections

DY1 DY2

DY3

DX3

DX2

DX1

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Comparison of Site

Measurements and Analysis Deflections

 – Simple Analysis

 – Beam and Spring Model

 – Finite Element Analysis

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The Reinforced Earth Company

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The Reinforced Earth Company

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Summary

Simple Analysis

 – Widely used

 – Simple to apply

 – Easy to understand

 – Wrong!

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Summary

Beam and Spring Model

 – Widely used

 – Simple to apply for a simplistic model, butcomparatively difficult for a realistic model

 – Easy to understand

 – Accuracy dependent on value of springconstants

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Summary Finite Element Analysis

 –  Not so widely used

 – Comparatively difficult to apply, particularly

for a realistic model – Less easy to understand

 – Selection of soil parameters based on standard

tests – Take account of all significant aspects of soil-

structure interaction

 – Gives consistent results, verified by site

measurements

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Conclusions - Analysis Methods

Simple elastic analysis – results are not reliable, particularly for high fills

Beam and spring model

 – essential to model staged loading –  may give good results, but selection of soil

 parameters is difficult

Finite element analysis

 – essential to model staged loading

 – good results with soil parameters based on

standard tests

 – able to model complex structures

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Conclusions - Analysis

Methodsand the winner 

is:-

 – Finite

ElementAnalysis!

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Projects

Homebush Bay Rail Link 

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Homebush Bay Rail Link

Animation of Finite Element

Analysis

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Projects

Olympic Park TechSpan

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Olympic Park TechSpan

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Actual Cross Section 

Semi Circular CrossSection 

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-20 -10 0 10 20

-100

0

100

200

Distance From Crow n, m

   M  o  m  e  n   t ,   k   N  m

Circular - Final Circular - Max Circular - Min

Funicular - Final Funicular - Max Funicular - Min

Moments on Buried ArchCircular and Funicular Curves

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Projects

Queensland Mine, River Crossing;

5500 Tonne live load

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Queensland Mine, River Crossing

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Projects

Olympic Dam Load Out Tunnel

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Olympic Dam Load Out Tunnel

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Summary

What is TechSpan?

What is new about it?

What is clever about it?

Why finite element analysis?

Does it work?

What does it mean for you?

Groupe TAI

Groupe TAI

The Reinforced Earth Company

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Conclusion

TechSpan Precast Concrete Arches Offer:

 – A sophisticated design and analysis system,

giving real savings in materials combined withexcellent durability

 – A flexible moulding system allowing the design

to suit the needs of the project

 – Simple and rapid erection

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