Urban Tunnelling: Constraints and Challenges - AFTES 2012-2013/2... · Urban Tunnelling:...
Transcript of Urban Tunnelling: Constraints and Challenges - AFTES 2012-2013/2... · Urban Tunnelling:...
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Urban Tunnelling:Constraints and Challenges
Master Course on Tunnels and Underground Space
Prof. Andre Assis, PhD (University of Brasilia / ITA)
Lyon (France) 11 January 2013
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5Conclusions
Urban Environment for Tunnelling
Design and Construction Aspects
Introduction
Lessons Learnt from Accidents
Contents
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Introduction
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•Increase of the urban population
•Environmental Era
•Tunnelling technology
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• Mass Transit Systems and Motorways
• Public Utilities
• Flood Control
• Revitalisation of City Centres
• Public Buildings
Demand of Urban Tunnelling
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Madrid Road Ring M-30
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• Safety– During Construction– During Operation
• Costs (GC = CC + SB)– Expropriation– Indemnification– Devaluation
Difficulties in Deciding forUnderground Structures
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Urban Tunnelling
Constraints
Public Decision
Alignment defined by demand
Geology imposed
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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
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General Trends in the Tunnelling Industry
High risk type construction methodsTrend towards design + build contractsOne-sided contract conditionsTight construction schedulesLow financial budgetsFierce competition in construction industries
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Decade 1990
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23.01.2013
“No construction project is risk free.
Risk can be managed, minimised,
shared, transferred or accepted.
It cannot be ignored.”
Sir Michael Latham, 1994
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Urban Environment for Tunnelling
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1Major concerns of urban tunnelling in soft ground and are related to (Kovari& Ramoni, 2004):
• Urban Environment
• Ground Conditions
• Risk Scenarios
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UrbanEnvironment
• Constraints for alignment• Shallow overburden• Existence of nearby structures• Foreign objects inside the ground• Restrictions for auxiliary works• Complex geometry
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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
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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
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ShallowOverburden Failure Mode
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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
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Existence of Nearby Structures
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Foreign Objects inside the Ground
• Direct conflict with tunnel alignment–Structural elements (foundation,
anchors, sheet piles)–Public utilities–Wells–Tree trunks and roots
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Foreign Objects inside the Ground
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Restrictions forAuxiliary Works• Exploitation• Shaft of attack• Ventilation towers• Muck transport and disposal• Dewatering• Ground improvement• Monitoring
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Ground Conditions
• Existing ground conditions– Recent geological formations– Fills– Frequent changing conditions (weathering)– Groundwater
• Complex Local Geology requiresGround Improvement and Reinforcement
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Face reinforcement by fiberglass
elements FGE
Steel pipes umbrella
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Purpose of Ground Improvement(Grasso, 2009)
Note:CONV: Conventional Tunnelling
TBM: 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 ● ●
Tunnelling
Conventional
Mechanised “TBM”
Difficult ground condition
Limit work condition
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Risk Scenarios
• Collapses up to surface• Damages due to tunnelling-induced
displacements
Design Criteria in terms of:- Failure- Admissible Displacements(damages)
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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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Design and Construction Aspects
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Principles of Tunnelling
• Ground excavation
• Support installation
• Monitoring
Ground-SupportInteraction
Bearing Ring of Reinforced Ground
ObservationalMethod
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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
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Tunnelling-Induced Displacements
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Loss of Ground Vp (m3/m)0 2 43 51
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7
Vs (m
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A'A"
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q
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A
before collapse
collapse
after collapse
colla
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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.
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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
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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 fo
r 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 fo
r consistency, foam for stickiness
1Water fo
r 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
rd a
pplic
ation
+ se
para
tion
ASt
anda
rd a
pplic
ation
+ se
para
tion
CFa
ce su
ppor
t diffi
cult:
susp
ensio
n+fill
ers
CFa
ce su
ppor
t diffi
cult:
susp
ensio
n+fill
ers
BAn
ti-clo
gging
-mea
sure
s, hig
h se
para
tion
effo
rt
BAn
ti-clo
gging
-mea
sure
s, hig
h se
para
tion
effo
rt
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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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2
3
4
5
1
Statistics on Causes of AccidentsLessons Learnt
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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
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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
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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
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Construction
• Faithful to the design changes in agreement
• Quality control (materials and services)
• Integrated risk and construction management contingency and emergency actions
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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
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Conclusions
2
3
4
5
1• 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
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