risk management in tunnelling 6-7 september 2017 · pdf file · 2018-01-31......

Risk Management in Tunnelling

6-7 September 2017– Santiago, ChileRisk Management Plan:

content, role and responsibilities, governance and organizationTarcisio B. Celestino

University of São PauloSão Carlos Engineering

School

Risk Management in Tunnelling6-7 September 2017– Santiago, Chile

Outline

1. Definitions

2. Risk Assessment and Management; risk evaluation

3. Risk Assessment

4. Special duties of the Client

5. Special duties of the Designer

6. Risk management at diferente stages of the Project

7. Deliverables for use by Contract Insurers

8. Site and ground investigation

9. Management of change of design


Risk Management Plan

“A document identifying the means and methods for the regular monitoring and review of the construction stage project risk register, of formally recording hazards and associated risks which arise during the course of the construction stage; of recording progress in the reduction/mitigation of the overall impact/number of risks; and of updating the construction phase project risk register and hence any changes to the project risk profile during the construction stage of the tunnel works”

(ITIG, 2006)


Risk register

“A formalized record of risks identified form the risk assessment process including full descriptive details of mitigation and control measures, risk owners and with appropriate cross references. The risk register is the primary means of recording and monitoring the risk management process.”

(ITIG, 2006)


Risk assessment

“The formalized process of identifying hazards and associated risks, of evaluating their consequences and probability of occurrence, and of preparing strategies as appropriate for preventative and contingent actions”

(ITIG, 2006)


Risk management

“The overall systematic process of risk assessment and providing for risk mitigation and control”

(ITIG, 2006)


Project risk profile

“An assessment of the residual risks at any point in time during tunnel works which potentially impact on the outcome of the project”

(ITIG, 2006)


Risk assessment and management


Quantification of ALARP concept

“Hazard identification and management of risk to ensure their reduction to a level ‘as low as reasonably practicable’ (ALARP) shall be integral considerations in planning, design, procurement and construction of tunnel works.”

(ITIG, 2006)

As low as reasonably practicable: quantitative guidelines in codes; reliability index -> probability of failure


Risk

• Code 4.1.2: Risk is defined as the combination of the consequences (or severity) of a ‘hazard’ and its likelihood.

• Deterministic design does not reflect potential deviations (load, properties)

• Probabilistic approach can explore that


Variability in geotechnicalengineering

• Potential consequences “... on cost, program, environment, third parties and existing facilities”


Definition of consequence classes(Eurocode 7)

Ultimate limit state


Recommended minimum valuesfor reliability index b (Eurocode 7)


Calculation of reliability index b

SourceTon VrouwenvelderTU Delft


Example



Calculation



Reliability index and probability of failure

b 1.3 2.3 3.1 3.7 4.2 4.7

P(F)=F(-b) 10-1 10-2 10-3 10-4 10-5 10-6


Calculation of reliability index in complex situations

• Calculation with different scenarios (load and parameters): Monte Carlo Simulation

• Time consuming with large numerical models

• Other methods available, e.g. point estimate method (Napa et al., 2017)


Risk assessment

• Risk assessment required at each stage of a Project

• Summarized in appropriate risk registers

• Risk registers shall clearly indicate the party responsiblefor control and management

• Parameters to be used in the assessment – probabilityof occurrence of a hazard and severity of impact – shellbe Project specific and appropriate to the project stage.

• Insurance should not be considered as a contingency ormitigation measure in risk assessment for tunnelWorks.


Risk registers

• Risk assessment and the subsequent preparation of risk registers: identification of the ownership of risks

• Detail clearly how the risks are to be allocated, controlled, mitigated and managed

• Risk registers: live documents. Updated as new information becomes available at different stages of the project. Example: lower insurance premium


Client role and responsiblity


Contract

• Standard form of contract e.g. FIDIC, Institution of Civil Engineers (UK)

• Specific contracts desirable. Danger of questionable innovations

• Importance of the connection between contract and risk policy; specific risk clauses required in the contract (Eskessen et al., 2004)

• ITA – FIDIC book: to be released in 2018


Client

• Shall have demonstrable technical and contractmanagement competence appropriate to the

• In the absence of appropriate experience, Client’srepresentative shall be appointed


ITA Strategic Plan

• Clients without technical tradition to beapproached

• Tendency to hire services based on minimum cost

• Higher rate of accidents in other áreas, e.g. dams

• Essential to keep high level of enginnering services


ITA Strategic Plan SWOT 2017


Potential problems in the relationship between client, designer and contractor

• Authoritarian attitude by client; Code 8.1.3: Designers should be provided with a brief, this brief and identify deficiencies or omissions. Example of designer asking for clarifications at tender stage; no answer from client.

• Statement from contractor in Washington DC during workshop on contractual practices: objectives during contract are make money, make money and do a good job.

• Clients trying to get as much from contractor as possible. Contractor: do the job and leave the site as soon as possible.


Potential problems in the relationship between client, designer and contractor

(cont.)• Authoritarian attitude by designer (sometimes due

to contract limitations but not always)

• Code 7.4.1: Provisions shall be made by the Client for reasonable time for tendering to reflect type of contract, complexity of the project…


Designer role and responsibility


Design

• Design where the risk of failure is extremely remote duringconstruction and design life

• Design risk assessment shall consider realistic variation in thedesign criteria and/or design values adopted e.g. rock joint orientation

• Consider intermediate stages of construction e.g. excavationstability

• Observational approach: pre-planned and pre-designedcontingency (monitoring frequency, ground treatment, additional support, ...) measures needed connected to‘trigger levels’

• Include assessment of the impact on third partyinfrastructure


Example of realistic variation

• Influence of joint orientation on excavation stability

• Tapered blocks may become potentially unstable blocks

• Anticipated roof instability may turn into wall instability


Impact on third party infrastructure(Celestino and Ferreira, 1996)

0

5

10

15

20

25

30

35

40

45

50

< 0

,5

0,5

- 1

1 -

1,5

1,5

- 2

2 -

2,5

2,5

- 3

3 -

3,5

3,5

- 4

4 -

4,5

4,5

- 5

>5

v s (%)

%

Volume loss recorded

Recorded repair cost (US$/m)

<70

<200

600


Constructability - design

• Appropriate design in terms of constructability including health and safety considerations and impacts on third parties

• Detail excavation support sequences for temporary conditions (important: not only final situation; e.g. Paulo Afonso IV underground power station; Tarbela diversion tunnels)


Paulo Afonso IV underground power station

∎

∎Cavern original design (unconstructable)


Paulo Afonso IV underground power station

• Problems with original design: almost no progress during construction

• 32.6m excavation span

• 1.8m thick reinforced concrete arch

• Fractured rock mass; RMR ~60

• Design changed during construction

• Pilot tunnel and two wing excavations

• 0.15m thick shotcrete and rockbolts

• Construction completed ahead of schedule


Risk management at different stages of the project

(Eskessen et al., 2004)


Deliverables for use by Contract Insurers


Deliverables for use by ContractInsurers (cont.)


Deliverables for use by Contract Insurers(cont.)


Site and ground investigation

• Shall be carried out in accordance with local National Standards and/or Codes of Practice

• If not available, adopt internationally recognized standard

• Provide sufficient information on pertaining site conditions, ground, groundwater, etc.

• “… shall be executed by organizations who are suitably qualified and experienced and hence competent for such work”


Typical borehole profile


N-SPT of two borehole campaignsat same locations


Management of change of design

• Design changes instructed by the Client orintriduced by the Contractor shall be reviewed; revised risk assessment submitted for approval

• Value engineering proposals submitted for approvalto the Client shall include statement settig out technical benefits and revised risk assessment. Example José Eusébio Shaft


José Eusébio ShaftLine 4 São Paulo Metro


José Eusébio ShaftLine 4 São Paulo Metro

• Tender design: secant bored piles to protect building foundation

• Execution of bored piles would get closer to building foundation

• Value engineering proposal: remove bored piles

• 20-cm shotcrete only at the upper part; 40 cm at lower part

• Cheaper, faster, safer


Final remarks

• Need for risk management in geotechnical projects, mainly in tunneling projects

• Potential for large damage to the Project, third parties, environment,...

• Risk managemnt activities at all stages of the Project

• Responsibilities by all parties involved: Client, Tenderers, designer, Contractor

• Need for flexible contract including risk clauses

• Good record of projects with risk management implemented


References

• Celestino, T.B. and Ferreira, A.A. (1996) Building damagesassociated to recente tunnels constructed for the São Paulo Subway. Proc. World Tunnel Congress 1996, ITA, Washington.

• Eskessen, S.D., Tengborg, P., Kampmann, J. and Veicherts, T.H. (2004) Guidelines for tunnelling risk management: InternationalTunnelling Association, Working Group No. 2. Tunnelling and Underground Space Technology, :19, 207-237.

• International Tunnelling Insurance Group (2006) A Code ofPractice for Risk Management of Tunnel Works.

• Napa- Garcia, G.F., Beck, A.T. Celestino, T.B. (2017) Reliability analyses of underground openings with the point estimate method. Tunnelling and Underground Space Technology, :64, 154-163.

Disclaimer

a) The speakers are presenting their own personal views and are not expressing the viewof the Foundation.

b) Papers and documents displayed or handed out during the Event are copyrighted. The participants must observe and comply with all applicable law regulations concerning the copyright.

Risk Management in Tunnelling

6-7 September 2017– Santiago, Chile

risk management in tunnelling 6-7 september 2017 · pdf file · 2018-01-31......

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