Specific Conditions and Requirements for Tunnelling in ... · PDF fileTUNNELLING IN URBAN AREA...

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Specific Conditions and Requirements for Specific Conditions and Requirements for Tunnelling in Urban Areas:Tunnelling in Urban Areas:

General and Environmental AspectsGeneral and Environmental Aspects

Prof. André P. Prof. André P. AssisAssis, PhD (UnB / ITA), PhD (UnB / ITA)

TRAINING MATERIAL PREPARED BY

5Conclusions and ReferencesConclusions and References

Conditions and Requirements for Urban TunnellingConditions and Requirements for Urban Tunnelling

Design AspectsDesign Aspects

IntroductionIntroduction

Construction MethodsConstruction Methods

Contents

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1

2/482/48Tunnelling in Urban AreasTunnelling in Urban Areas

Introduction

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Tunnelling in Urban AreasTunnelling in Urban Areas

•Increase of the urban population (after the 2nd World War)

•Environmental Era (after 1960)

•Tunnelling technology

Introduction

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Environmental Era Urban Trend

Introduction

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• Better Behaviour Understanding– Control of settlements and displacements– Evaluation of induced damages

• Technology Advances– Works safer, cheaper and built in short time– New generation of TBMs (pressurised face) –

tunnelling in any geological conditions and urban environment

• Seismic resistance

Favourable Factorsfor Urban Tunnelling

Introduction

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• Mass Transit Systems and Motorways

• Public Utilities (water, sewage, cables etc.)

• Flood Control

• Revitalisation of City Centres

• Public Buildings

Demand of Urban Tunnelling

Introduction

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• Safety– During Construction– During Operation

• Costs

Difficulties in Deciding forUnderground Structures

Introduction

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Difficulties in Deciding forUnderground Structures Costs

3.0Tunnel (double track)

Tunnel (single track)

2.5Cut & Cover *

1.5Viaduct *

1.0Surface *

Cost RatioConstructionMethods

* Not including surface land buying

3.0

Introduction

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Global Cost Assessment for Underground Structures• Cost of the surface

space• Indenisation during

construction (negative impacts of surface works)

• Devaluation of real estate nearby to infrastructure

Introduction

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11Urban Tunnelling


TunnellingTunnellingMethodsMethods

ConventionalConventional

MechanisedMechanisedSpecialSpecial

Soft GroundSoft GroundHard GroundHard Ground

Mix GroundMix Ground

Introduction

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Urban Urban TunnellingTunnelling

Soft Ground Soft Ground TunnellingTunnelling


MechanisedMechanised

SpecialSpecial

Ground ImprovementGround Improvement

Full Face ExcavationFull Face Excavation

Trench MethodsTrench Methods


Introduction

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• Main concern during excavation is the stability of the opening

• Most cases of soft ground tunnelling are in urban environment

• Tunnelling-induced displacement field may reach surface and affect existing nearby structures

• Design may be dominated by admissible-displacement criteria


Soft Ground Tunnelling

Conditions and Requirements

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11Major concerns of soft ground and urban tunnelling are related to (Kovari & Ramoni, 2004):

• Urban Environment

• Ground Conditions

• Risk Scenarios


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• Shallow overburden• Existence of nearby structures• Foreign objects inside the ground• Constraints for alignment• Restrictions for auxiliary works• High visibility of damage



Urban Environment

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• Access ways as shallow as possible• Larger and larger tunnel diameters

• Concept of Shallow Tunnel– Type of Failure– Displacement field up to surface or

existing structures

Shallow Overburden



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11 Shallow Overburden

(Sauer & Mergelsberg, 2003)(Sauer & Mergelsberg, 2003)



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• Types of structures (transport ways, public utilities, buildings, historical sites etc.)

• Affected by the induced displacement field, but they also affect it

• Sensitivity to potential damages


Conditions and RequirementsExistence of Nearby Structures

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Existence of Nearby Structures



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• Direct conflict with tunnel alignment–Structural elements (foundation,

anchors, sheet piles)–Public utilities–Wells–Tree trunks and roots


Conditions and RequirementsForeign Objects inside the Ground

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Foreign Objects inside the Ground



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• Usually dominated by transport demand

• Influenced by urban constraints (p.ex. location of ventilation towers)

• Preferable under public ground• Unavoidable to underpass existing

structures• Cope with existing ground conditions


Conditions and RequirementsConstraints for Alignment

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• Exploitation• Shaft of attack• Ventilation towers• Muck transport and disposal• Dewatering• Ground improvement• Monitoring


Conditions and RequirementsRestrictions for Auxiliary Works

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High Visibility of Damages

• Sensitivity of potential damages

• Loss of public confidence is very jeopardising to tunnelling industry



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• Collapses up to surface• Damages due to tunnelling-induced

displacements

Design Criteria in terms of:Design Criteria in terms of:--FailureFailure--Admissible DisplacementsAdmissible Displacements

Risk Scenarios



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11 Ground Conditions• Existing ground conditions

– Recent geological formations– Fills– Frequent changing conditions

(weathering)– Groundwater

• Ground Improvement and ReinforcementTunnelling in Urban AreasTunnelling in Urban Areas


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Ground Conditions

Clay Sand

Water level

Fill

Tunnel



Design Aspects

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• Ground excavation

• Support installation

• Monitoring

Principles of Tunnelling

Ground-SupportInteraction

Bearing Ring of Reinforced Ground

ObservationalMethod


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11 Ground-SupportInteraction

upsps

u

po

ps

u

po

Design Aspects


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11Geology

Lab and In-Situ Tests

Designer Experience

Global Investigation

Geotechnical Properties

Excavation Method and Support System

Structural Model and Design Predictions

Ok?

Construction

Yes

NoElements of

Tunnel Design

Design Aspects


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11 Design Aspects

Stress-Strain-Displacement Analysis• Empirical Formulations• Closed-Form Solutions

– Simple Geometry– Homogeneous and Isotropic Media– Linear Elastic Behaviour

• Numerical Methods– Boundary Element– Finite Element– Discrete Element

Media

CHILE

Media

DIANETunnelling in Urban AreasTunnelling in Urban Areas

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11 Tunnelling-Induced Displacements

Design Aspects


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11Checking for Tunnelling-Induced Damages• Calculate the green field settlement

trough• For structures inside the settlement

trough, check potential damages due to green field settlements and distortions

• For those in critical state, run a more accurate analysis taking into account the structure stiffness

• Perform reinforcement when required

Design Aspects


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Contractor Experience Construction

Ok?

Yes

No

Elements of

Construction

Monitoring

Ok?

Yes

No

Safe

Construction Methods


4 m6 m

H - 2 m

(H - 2 m) / 2

H

M1

E1

E2P1

M2M4 M3 M5

P2

P4

P6

P3

P7

P5

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Soft Ground Soft Ground TunnellingTunnelling


MechanisedMechanised

SpecialSpecial

Ground ImprovementGround Improvement

Full Face ExcavationFull Face Excavation

Trench MethodsTrench Methods



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• Open Trenches• Cut-and-Cover Structures

– Direct and Inverse Excavation• Door-Frame Method

• Immersed Tunnels– Caisson and Door-Frame Methods


Special Methods


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11 Construction Methods

Door Frame Method



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• Excavation• Ground Conditioning• Support Installation

Stress RelaxationStress Relaxation


Conventional Tunnelling


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Support Installation


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11 Construction MethodsTunnelWaterproofing


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• Excavation• Support Installation

Avoid or MinimiseAvoid or MinimiseStress RelaxationStress Relaxation


Mechanised Tunnelling


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MechanisedTunnelling


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11 Construction MethodsRelevant factors for the TBM selection are (Kovari & Ramoni, 2004):• Grain size distribution• Type of predominant mineral (quartz

contents)• Soil strength (cohesion)• Overburden• Heterogeneity (mix ground, weathering)• Piezometric pressure


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11 Construction MethodsConventional versus Mechanised

Tunnelling• Geometry Flexibility• Geology Flexibility• Contractual

Flexibility• Political Flexibility• Lower costs for short

tunnels and cheaper labour

• Lower impact to ground• Higher and more

constant quality (industrial process)

• Lower load to workers• Safer• More accurate costs and

schedule


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11 Construction MethodsConventional versus Mechanised

Tunnelling



Conclusions and References

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11• Majors concerns are opening stability

and control displacement field• Soft ground tunnelling is likely

dominated by failure and admissible displacement criteria

• Ground conditioning (improvement and reinforcement) plays an important role

• Tunnelling methods and technology vary depending on geology, tunnel location, length and geometry, local tradition etc.


Conclusions and References

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• Assis, A.P. (2005). Conventional Tunnelling: The Example of the Brasilia Metro. ITA Training Course, ITA / Technical University of Istanbul, Istanbul, Turkey (www.ita-aites.org).

• Kovari, K. & Ramoni. M. (2004). Urban Tunnelling in Soft Ground Using TBMs. International Congress on Mechanised Tunnelling: Challenging Case Histories, Keynote Lecture, Politecnico di Torino, Turin, Italy (www.ita-aites.org).

• Sauer, G. & Mergelsberg, W.A. (2003). Tunnelling and its toolbox(Tunnelling… and beyond). Conference on Earth Retention Systems, ASCE / DFI / ADSC, New York, USA.


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Disclaimer for the reports of ITA working groupsThe International Tunnelling Association (ITA) publishes this report to, in accordance with its statutes, facilitate the exchange of information, in order:

- to encourage planning of the subsurface for the benefit of the public, environment and sustainable development

- to promote advances in planning, design, construction, maintenance and safety of tunnels and underground space, by bringing together information thereon and by studying questions related thereto.

However ITA accepts no responsibility or liability whatsoever with regard to the material published in this report.

This material is:

- information of a general nature only, which is not intended to address the specific circumstances of any particular individual or entity;

- not necessarily comprehensive, complete, accurate or up to date;

- sometimes collected from external sources over which ITA services have no control and for which ITA assumes no responsibility;

- not professional or legal advice (if you need specific advice, you should always consult a suitably qualified professional).

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