urban tunnelling: constraints and challenges 2011-2012... · urban tunnelling: constraints and...
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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
2
3
4
1
Introduction
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33
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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
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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
Ground Conditions
• Existing ground conditions– Recent geological formations– Fills– Frequent changing conditions (weathering)– Groundwater
• Complex Local Geology � requires �� Ground Improvement and Reinforcement
Face reinforcement Face reinforcement by fiberglass by fiberglass
elements FGEelements FGE
Steel pipes Steel pipes umbrellaumbrella
Purpose of Ground Improvement(Grasso, 2009)
Note:Note:CONVCONV: Conventional Tunnelling : Conventional Tunnelling
TBMTBM: Mechanised Tunnelling: Mechanised Tunnelling
Needs for Ground Improvement CONV TBM
Geo-problems (thrust zone, shear zone, fault zone especially when water-bearing, zone of very poor quality ground, Kartstic voids …) � �
Insufficient self-supporting time �
Unacceptable ground surface settlement � �
Very low overburden underpasses in urban area � �
Keeping natural water table � �
Global face stability �
Face stability during machine maintenance �
Modify Ground Reaction Curve (GRC) (radial and longitudinal directions) � �
Water inflow with high pressure � �
Interaction of newly designed underground structures with those excavated earlier � �
Flowing ground � �
TunnellingTunnelling
ConventionalConventional
Mechanised Mechanised ““TBMTBM””
Difficult ground conditionDifficult ground condition
Limit work conditionLimit work condition
Risk Scenarios
• Collapses up to surface• Damages due to tunnelling-induced
displacements
Design Criteria in terms of:Design Criteria in terms of:-- FailureFailure-- Admissible DisplacementsAdmissible Displacements
(damages)(damages)
High Visibility of Damages
• Sensitivity of potential damages
• Loss of public confidence is very jeopardising to tunnelling industry
Design and Construction Aspects
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Principles of Tunnelling
• Ground excavation
• Support installation
• Monitoring
Ground-SupportInteraction �
Bearing Ring of Reinforced Ground
ObservationalMethod
Geology
Lab and In-Situ Tests
Designer Experience
Investigation
Geotechnical Properties
Excavation Method and Support System
Structural Model and Design Predictions
Ok?
Construction
Yes
NoElements of
Tunnel Design
Tunnelling-Induced Displacements
Vs = VpVs = Vp
Loss of Ground Vp (mLoss of Ground Vp (m33/m)/m)00 22 4433 5511
1122
33445566
77
Vs (m
Vs (m
33 /m)
/m)
A'A"
BB'
q
p
eei
A
before collapse
collapse
after collapse
colla
pse
crite
rion
Checking 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
• Mair, R. (2011). ITA Muir Wood Lecture.
Contractor Experience Construction
Ok?
Yes
NoElements of
Construction
Monitoring
Ok?
Yes
No
Safe
4 m6 m
H - 2 m
(H - 2 m) / 2
H
M1
E1
E2P1
M2M4 M3 M5
P2
P4
P6
P3
P7
P5
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
Per
cent
Pas
sing
[%]
Particle Size [mm]
0
10
20
30
60 10020620,60,20,060,020,0060,002
40
50
60
70
80
90
100
EPB
1Water for consistency, foam for stickiness
2Foam
3Foam + Polymers, water pressure < 2 bar
4Foam + Polymers + fines, no water pressure
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
Per
cent
Pas
sing
[%]
Particle Size [mm]
0
10
20
30
60 10020620,60,20,060,020,0060,002
40
50
60
70
80
90
100
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
Per
cent
Pas
sing
[%]
Particle Size [mm]
0
10
20
30
60 10020620,60,20,060,020,0060,002
40
50
60
70
80
90
100
EPB
1Water for consistency, foam for stickiness
1Water for consistency, foam for stickiness
2Foam
2Foam
3Foam + Polymers, water pressure < 2 bar
3Foam + Polymers, water pressure < 2 bar
4Foam + Polymers + fines, no water pressure
4Foam + Polymers + fines, no water pressure
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
Per
cent
Pas
sing
[%]
Particle Size [mm]
0
10
20
30
60 10020620,60,20,060,020,0060,002
40
50
60
70
80
90
100
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
GRAVELSANDSILTCLAY
coarsemediumfinecoarsemediumfinecoarsemediumfine
Per
cent
Pas
sing
[%]
Particle Size [mm]
0
10
20
30
60 10020620,60,20,060,020,0060,002
40
50
60
70
80
90
100
Fluid-Supported
ASt
anda
rdap
plica
tion
+se
para
tion
ASt
anda
rdap
plica
tion
+se
para
tion
CFa
cesu
ppor
t diffi
cult:
susp
ensio
n+fill
ers
CFa
cesu
ppor
t diffi
cult:
susp
ensio
n+fill
ers
BAn
ti-clo
ggin
g-m
easu
res,
high
sepa
ratio
nef
fort
BAn
ti-clo
ggin
g-m
easu
res,
high
sepa
ratio
nef
fort
Monitoring andTBM Active Control
Control system• Controlling of Boring
Process: guide parameters from interdisciplinary processing of geotechnical, geodetic and machine data
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33
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11
Statistics on Causes of AccidentsLessons Learnt
Pre-Bidding Documents• Geological investigation and geotechnical
data as much as possible
• Full disclosure of all GG data– Geological model– GG Data Report– Geotechnical Base Report
• Different Ground Conditions � Owner
Design Documents
• Geomechanical model• Structural model of the tunnel• Assumptions, completeness and type of
calculations and simulations– Continuum media?– Type of model and parameters– 2D or 3D analysis?
• Monitoring � threshold values• Design Reviewer
Design during Construction
• Complementary investigation and mapping of all GG conditions
• Monitoring interpretation
• Design back-analysis
• Design Validation
-25
-20
-15
-10
-5
0
5
23/1
1/06
03/1
2/06
13/1
2/06
23/1
2/06
02/0
1/07
12/0
1/07
Data
Rec
alqu
e (m
m) 7.0+86 - P1
7.0+86 - P2
7.0+86 - P3
7.0+96 - P1
7.0+96 - P2
7.0+96 - P3
7.1+06 - P1
7.1+06 - P2
7.1+06 - P3
7.1+15 - P1
7.1+15 - P2
7.1+15 - P3
Construction
• Faithful to the design � changes in agreement
• Quality control (materials and services)
• Integrated risk and construction management � contingency and emergency actions
Role of Contracts
• Keep fair balance– quality, schedule and costs
• Mix of technical and performance specifications � quality control
• Independent auditing and full disclosure of control parameters
• Incorporate risk management and risk sharing
Conclusions
22
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11• Urban tunnelling is a great and
increasing demand worldwide
• Urban tunnelling is challenging due to urban environment and its constraints
• Urban tunnelling is likely dominated by limit admissible damage criteria
• Risk management has to be incorporated in all project phases