Lessons Learnt from Accidents in Urban Tunnels

Prof. André P. Assis, PhD(UnB / ITA)

EPFL Master on Advanced TunnellingLausanne, Switzerland – May 2011

Introduction

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

Decade 1990

Major Tunnel Losses since 1994

1994 Heathrow Express Link, GB Collapse US$ 141 mio

1994 Metro Taipei, Taiwan Collapse US$ 12 mio

1994 Munich Metro, Germany Collapse US$ 4 mi

1995 Metro Los Angeles, USA Collapse US$ 9 mio1995 Metro Taipei, Taiwan Collapse US$ 29 mio

PROJECT CAUSE LOSS

1999 Hull Yorkshire Tunnel, UK Collapse US$ 55 mio

1999 TAV Bologna - Florence, Italy Collapse US$ 9 mio2000 Metro Taegu, Korea Collapse US$ 24 mio

Major Tunnel Losses since 1994

PROJECT CAUSE LOSS2000 TAV Bologna - Florence, Italy Collapse US$ 12 mio

2002 Taiwan High Speed Railway Collapse US$ 30 mio

2003 Shanghai Metro, PRC Collapse US$ 80 mio2004 Singapore Metro, S’pore Collapse t.b.a.

2005 Barcelona Metro, Spain Collapse t.b.a.2005 Lausanne Metro, Switzerland Collapse t.b.a.2005 Lane Cove Tunnel, Sydney Collapse t.b.a.

2005 Kaohsiung Metro, Taiwan Collapse t.b.a.

2007 Sao Paulo Metro, Brazil Collapse t.b.a.and so on …

Statistics on Causes of Accidents

Accidents DuringConstruction: Last

Decade Scenario

Significant increase in the number of claimsInsurance income <<< Claims outcomeInsurance paid >>> Initial cost of the work Difficulties to insure underground works

Options of the Insurance Market

Stop insure underground works

Increase insurance prices and tight conditions

Professional approach to the problem involving all related parts

Focus on other markets

Insurance may become not feasible

Proposal of a code of practice for risk management

Aims and Results of the Code of Practice for Risk Management

Establish minimum standards for evaluation of risks and procedures of risk management

Clear definition of responsibilities of all involved parts

Reduce probability of lossesReduce number and size of claimsRe-establish the trust of insurance companiesTransfer the concept of good practice to other market sectors

18.05.2011

“No construction project is risk free.

Risk can be managed, minimised,

shared, transferred or accepted.

It cannot be ignored.”

Sir Michael Latham, 1994

IntroductionIPT Investigation Work and ReportMain IPT Report FindingsConclusions and Recommendations

Lessons Learnt from the PinheirosStation Accident in Sao Paulo, Brazil

Barton, N. (March, 2008)

IPT (June, 2008)

CVA (August, 2008)

Existing Technical Reports on the PinheirosStation Accident

Introduction: SP Metro Line 4

Introduction: SP Metro Line 4

PinheirosStation

Introduction: Pinheiros Station

Pinheiros StationDesign (primary

support)

Pinheiros StationDesign (final support)

Pinheiros StationConstruction

Scheme

Introduction:Pinheiros Station

Accident

Occurred on 12/01/2007During the bench excavation, very close of arriving to the shaftFirst failure signs ~14h30Daylight collapse at 14h54Enormous material damages and 7 fatalities

IPT commissioned the technical investigation

IPT Investigation Work and Report

IPT Commission (team of in-house specialists)Board of Consultants (4 Brazilians and 2 foreigners)Independent Auditing Firm (RinaInternational)

Desk StudiesFollowing-up of the collapse debris excavationInterviews with involved staff from all parties

Chapters 1-3: Introduction, objectives & scopeChapter 4: Urban tunnellingChapter 5: Trends in contractual practicesChapter 6: Pre-bidding knowledgeChapter 7: Contractual aspects of Line 4Chapter 8: Design and constructionChapter 9: CollapseChapter 10: Mechanism and causesChapter 11: Conclusions and Lessons

IPT Report (main report 384 p.+ 46 appendices ~3000 p. + video)

10 years of studies till biddingAmount of geological and geotechnical investigation and level of engineering design had been continuously upgraded very reasonable and adequateGeological-geomechanical model

Hasui (1993)IPT (1997)Figueiredo Ferraz (2001)

IPT Main Report:Pre-Bidding

Caucaia Shear Zone

PinheirosStation

N

Geological-Geomechanical Model

Pre-Bidding

From impressiom packer in Pinheiros station area and reginal surveys (319 poles) From scanlines on the

final surface (26 and 522 poles)

Structural Geology – 4 families

Geologicalinterpretation

considering strutcturalinformation

142610 142630 142650 142670 142690 142710 142730 142750 142770 142790

178120

178140

178160

178180

178200

SR-01

SR-02

SR-03

SR-04

SR-05

SR-06

SR-07SR-08

DE-SM-ML4-23

SM-8700

SM-8701

SM-8702

SM-8703

SM-8704

SM-8705

SM-8706

SM-8707

SM-8708

SM-8714

SM-8719

SM-8720SP-8709

SP-8710

SP-8711SR-8584

DAS

NAÇ

ÕS

UN

IDA

S

SM-6802

SM-6530

SM-6532

SM-6803

Filonite (SR-07)

142645 142665 142685 142705 142725 142745 142765 142785178125

178145

178165

178185

178205

178225

178245

178125

178145

178165

178185

178205

178225

178245

142645 142665 142685 142705 142725 142745 142765 142785

Pinheiros Station: Geomechanical sections obtained from 3D interpolation using structural

geology information

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150680

690

700

710

720

680

690

700

710

720

WSW ENE

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140680

690

700

710

720

680

690

700

710

720

WSW ENE

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140680

690

700

710

720

680

690

700

710

720

WSW ENE

Longitudinal sections (central, north side and south side)

Blue - fill

Yellow – alluvium

Green – tertiary sediments

Brown – weathered soil

Dark gray – RMR IV

Medium gray – RMR III

Light gray – RMR II

(rock mass classification from designer)

680

690

700

710

720

680

690

700

710

720

0 10 20 30 40 50 60 70 80 90 100 110 120

NNW SSEeixo entrevias

680

690

700

710

720

680

690

700

710

720

0 10 20 30 40 50 60 70 80 90 100 110 120

NNW SSEeixo entrevias

680

690

700

710

720

680

690

700

710

720

0 10 20 30 40 50 60 70 80 90 100 110 120

NNW SSEeixo entrevias

680

690

700

710

720

680

690

700

710

720

0 10 20 30 40 50 60 70 80 90 100 110 120

NNW SSEeixo entrevias

Cross-sections obtained from 3D interpolation

Sub-vertical alternation of granitic and biotitic gneiss, with variable thickness (sub-parallel to the tunnel longitudinal section)Four families of discontinuitiesRockmass is heterogeneous and anisotropic due to discontinuities and uneven weathering bedrock surface as egg box type

Post-bidding investigation confirmed the GG model developed during the pre-bidding design

Geological-Geomechanical

Model

Geomechanical model adopted did not consider the anisotropy due to discontinuities

Assumptions and calculations2D analysis shaft effect neglectedOversimplified constitutive law for the soils above tunnelGround assumed fully drained

Design analyses indicated critical stability conditions during the bench excavation phase

IPT Main Report:Design Shortcomings

Monitoring and InstrumentationInstruments

4 sections (5 convergence pins)4 sections (3 extensometers)Some open-pipe piezometers

Threshold values for the instrumentationShaft: all threshold values definedTunnel: only the expected value calculated, but no definition of the warning and emergency values (qualitative criteria)

No evidence of backanalyses

IPT Main Report:Design Shortcomings

Quality control based on self-certificationPoor control of methods and materials

Forepoling fillingQuantity of sprayed concrete fibresEarly-age strength of sprayed concrete

Deficient quality managementInternal auditing systemGeomechanical mappingInstrumentation data interpretation

IPT Main Report:Construction Aspects

Risk Management (contingency and emergency actions)

Three main design violations during construction

Inversion of the excavation direction of the bench towards the shaftIncrease of the bench height (4 to ~5 m)Change of the bench excavation sequence (also the rate: 1.8 m/d in January 2007 and 0.9 m/day in December 2006)

IPT Main Report:Construction Aspects

-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

-40,0

-35,0

-30,0

-25,0

-20,0

-15,0

-10,0

-5,0

0,0

5,0

15/0

8/06

25/0

8/06

04/0

9/06

14/0

9/06

24/0

9/06

04/1

0/06

14/1

0/06

24/1

0/06

03/1

1/06

13/1

1/06

23/1

1/06

03/1

2/06

13/1

2/06

23/1

2/06

02/0

1/07

12/0

1/07

22/0

1/07

Data

Con

verg

ênci

a (m

m)

7.0+867.0+967.1+67.1+15

Few Days before

Collapse

Meeting on 11/01/2007

Installation of bolts in the tunnel bench walls decided No enough bolts in stock, despite it was forecasted

in the design as contingency action (15% installed but all borehole drilled)

Three blasting on the 12/01/2007 (two around 8 h, one in each platform tunnel, and a third one around 12 h)

No clear definition on the need to stop the works (contradictory version among participants)

The Colapse

Fall of small concrete blocks

Fracture propagation from the shaft till 1/3 of the tunnel length, position 11 h

Fall of 6 to 8 lattice girders in the left-hand side wall Colapse daylight on surface at

14h54 Colapse of the north wall of the

shaft at 15h30 (last event)

Main Report Findings:Collapse Evidences

eixo

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

23/1

1/06

03/1

2/06

13/1

2/06

23/1

2/06

02/0

1/07

12/0

1/07

22/0

1/07

Data

Rec

alqu

e (m

m)

TN.E-1TN.E-2TN.E-3TN.F-1TN.F-2TN.F-3TN.G-1TN.G-2TN.G-3MS1TN.H1TN.H-3

Instrument Position Calculated(mm)

Observed on 11/01/07 (mm)

Observed / Calculated

ExtensometerAxis -0,7 -11 17

Lateral Wall -0,7 -12 19

Convergence Pins

(Settlement)

Axis -0,7 -7 10

Upper -0,9 -20 22

Lower -0,5 -7 13Convergence P2-P3 -0,2 -21 95

13/1

2

23/1

2

02/0

1/20

07

Collapse:Instrumentation

Data

Instrumentation evidences

Main Report Findings:Collapse Evidences

0

5

10

15

20

25

30

0

5

10

15

20

25

30

ESTACAS 7,0+86 / 7,0+97 / 7,1+06 / 7,1+150

5

10

15

20

25

30

0

5

10

15

20

25

30

ESTACAS 7,0+86 / 7,0+97 / 7,1+06 / 7,1+15

NOV29

DEZ15

DEZ27

JAN02

JAN08

JAN09

JAN10

JAN11

JAN12

JAN12T

PINO 2 PINO 3

VISTA GERAL DOS ESCOMBROS

Debris position evidences

Main Report Findings:Collapse Evidences

Section 7,0+87

Section 7,1+04

Section 7,1+13

Main Findings: Collapse Mechanism

142735 142745 142755 142765 142775 142785

142735 142745 142755 142765 142775 142785

178165

178175

178185

178195

178205

178165

178175

178185

178195

178205

?

P-2

P-2

P-2

P-2

P-3

P-3

P-3

P-3

TN.E1

TN.E2

TN.E3

TN.F1

TN.F2

TN.F3

TN.G1

TN.G2

TN.G3

TN.H1

TN.H3

TN.E1

TN.E2

TN.E3

TN.F1

TN.F2

TN.F3

TN.G1

TN.G2

TN.G3

TN.H1

TN.H3

Medidas de recalque nos tassômetros referenciadas a 11/01/07

Non-Validated DesignOversimplified geomechanical modelStructural tunnel modelAssumptions and completeness of calculations and simulationsNo definition of threshold values for monitoringDeficient GG mappingDeficient analysis and interpretation of monitoring dataNo evidence of back-analyses and design validation

Main Report Findings:Risk Factors and Causes

Non-Validated Construction ProcedureChange of excavation directionIncrease of bench heightChange of blasting schemeDeficient quality controlIncrease of excavation rateDeficient construction management (lack of bolts)No decision to stop worksDeficient plans of contingency and emergency actions

Main Report Findings:Risk Factors and Causes

Main Report Findings:Risk Factors and Causes

Non-validated design

Non-validated construction procedure and poor management

Collapse of Pinheiros Station

Accident Collapse and its Consequences

Presence of transit and pedestrians

Fault of the emergency plan of actions

Risk Factors and Causes:Foreseeability and Other Aspects

Different ground conditionsExcessive rainSeismic activityPipe leakage

ForeseeabilityClear under good practice of engineering Misty by faults in several engineering processes

-16,0

-14,0

-12,0

-10,0

-8,0

-6,0

-4,0

-2,0

0,0

2,0

4,0

29/1

1/06

04/1

2/06

09/1

2/06

14/1

2/06

19/1

2/06

24/1

2/06

29/1

2/06

03/0

1/07

Data

Rec

alqu

e (m

m)

7080

7085

7090

7095

7100

7105

7110

7115

7120

7125

7130

Esta

ca (m

)

P1P2P3P4P5avanço

Geological model complex but data was fully disclosure no major changes by no means claim based on Different Ground ConditionsCauses are related to shortcomings in engineering processes (design and construction)

systemic fault processLessons and recommendations to engineering and contractual arrangements

Conclusions

Recommendations for Future

Contractual Arrangements

Keep fair balance among quality, schedule and costsMix of technical and performance specifications

quality controlIndependent auditing and full disclosure of control parameters owners must keep controlIncorporate risk management and risk sharing

Pre-Bidding DocumentsGeological and geotechnical data as much as possibleFull disclosure of all GG data

Geological modelGG Data ReportGeotechnical Base Report

Different Ground Conditions Owner

Lessons Learnt

Design DocumentsGeomechanical modelStructural model of the tunnelAssumptions, completeness and type of calculations and simulations

Continuum media?Type of model and parameters2D or 3D analysis?

Monitoring threshold valuesDesign Reviewer

Lessons Learnt

Design during Construction

Complementary investigation and mapping of all GG conditions

Monitoring interpretation

Design back-analysis

Design Validation

Lessons Learnt

ConstructionFaithful to the design changes in agreement

Quality control (materials and services)

Integrated risk and construction management contingency and emergency actions

Lessons Learnt

Role of Contracts

Keep fair balance among quality, schedule and costsMix of technical and performance specifications quality controlIndependent auditing and full disclosure of control parameters

Incorporate risk management and risk sharing

Lessons Learnt

Urban tunnelling is a great and increasing demand worldwideUrban tunnelling is challenging due to urban environment and constraintsUrban tunnelling is likely dominated by limit admissible damage criteriaRisk management has to be incorporated in all project phases

The worst happening is not to have an accident, it is to learn nothing from it.

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).Munich Re (2006). Code of Practice for Risk Management of Tunnel Works: Future Tunnelling Insurance from the Insurer´s Point of View. ITA Open Session, ITA World Tunnel Congress, Seoul, South Korea.Munich Re (2007). Insurance Cover as Part of the General Risk Management Strategy. ITA Open Session on Public Private Partnership Projects, ITA World Tunnel Congress, Prague, Czech Republic.Seidenfuss, T. (2006). Collapses in Tunnelling. Master Thesis, Stuttgart University of Applied Sciences, Stuttgart, Germany, 179 p.