Urban Tunnelling: Urban Tunnelling: Constraints and Challenges Constraints and Challenges (Inaugural Lecture of the Master Course on Tunnels and Underground Space) ITA/AITES ITA/AITES Prof. Andre Assis, PhD Prof. Andre Assis, PhD (University of Brasilia / ITA) (University of Brasilia / ITA) AFTES International Congress Lyon 2011 AFTES International Congress Lyon 2011 “ “ Underground Space for Tomorrow Underground Space for Tomorrow ” ” Lyon (France) 17 Lyon (France) 17 - - 19 October 2011 19 October 2011
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Urban Tunnelling:Urban Tunnelling:Constraints and ChallengesConstraints and Challenges
(Inaugural Lecture of the Master Course on Tunnels and Underground Space)
ITA/AITESITA/AITES
Prof. Andre Assis, PhD Prof. Andre Assis, PhD (University of Brasilia / ITA)(University of Brasilia / ITA)
AFTES International Congress Lyon 2011AFTES International Congress Lyon 2011““Underground Space for TomorrowUnderground Space for Tomorrow””
Lyon (France) 17Lyon (France) 17--19 October 201119 October 2011
5ConclusionsConclusions
Urban Environment for TunnellingUrban Environment for Tunnelling
Design and Construction AspectsDesign and Construction Aspects
IntroductionIntroduction
Lessons Learnt from AccidentsLessons Learnt from Accidents
Contents
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3
4
1
Introduction
22
33
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55
11
•Increase of the urban population
•Environmental Era
•Tunnelling technology
4/404/40
• Mass Transit Systems and Motorways
• Public Utilities
• Flood Control
• Revitalisation of City Centres
• Public Buildings
Demand of Urban Tunnelling
Madrid Road Ring M-30
6/406/40
• Safety– During Construction– During Operation
• Costs (GC = CC + SB)– Expropriation– Indemnification– Devaluation
Difficulties in Deciding forUnderground Structures
Urban Urban TunnellingTunnelling��
ConstraintsConstraints
Public DecisionPublic Decision
Alignment defined by Alignment defined by demanddemand
Geology imposedGeology imposed
Urban Tunnelling in Soft Ground• Most cases of soft ground tunnelling are
in urban environment• Main concern during excavation is the
stability of the opening• Tunnelling-induced displacement field
may reach surface and affect existing nearby structures
• Design may be dominated by admissible-displacement criteria
General Trends in the Tunnelling Industry� High risk type construction methods� Trend towards design + build contracts� One-sided contract conditions� Tight construction schedules� Low financial budgets� Fierce competition in construction
industries
Decade 1990Decade 1990
25.11.2011
““No construction project is risk free.No construction project is risk free.
Risk can be managed, minimised,Risk can be managed, minimised,
shared, transferred or accepted.shared, transferred or accepted.
It cannot be ignored.It cannot be ignored.””
Sir Michael Latham, 1994Sir Michael Latham, 1994
Urban Environment for Tunnelling
13/4013/40
22
33
44
55
11Major concerns of urban tunnelling in soft ground and are related to (Kovari & Ramoni, 2004):
• Urban Environment
• Ground Conditions
• Risk Scenarios
UrbanEnvironment
• Constraints for alignment• Shallow overburden• Existence of nearby structures• Foreign objects inside the ground• Restrictions for auxiliary works• Complex geometry
Constraintsfor Alignment
• Usually dominated by the tunnel 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
Shallow Overburden
• 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
ShallowOverburden �Failure Mode
Existence of Nearby Structures
• Types of structures (transport ways, public utilities, buildings, historical sites etc.)
• Nearby structures are affected by the induced displacement field, but they also affect the displacement field � Interaction
• Sensitivity to potential damages
Existence of Nearby Structures
Foreign Objects inside the Ground
• Direct conflict with tunnel alignment–Structural elements (foundation,
anchors, sheet piles)–Public utilities–Wells–Tree trunks and roots
Foreign Objects inside the Ground
Restrictions forAuxiliary Works• Exploitation• Shaft of attack• Ventilation towers• Muck transport and disposal• Dewatering• Ground improvement• Monitoring