Geotechnical risk management for tunneling beneath open water

of the investigations indicated that the Frøya tunnel
required thorough evaluations to assess its feasibility,
and that special routines be implemented during
planning and construction.
As a part of this, two groups were established to
evaluate the feasibility of the tunnel. In their two
independent reports excavation methods and rock support
were analyzed, supported by a cost estimate and
risk assessment. Construction time and cost estimates
were based on a detailed prognosis of the expected
ground conditions, and the estimate proved to correspond
quite well with reality (Palmstrøm et.al, 2000).
6 DISCUSSION AND CONCLUSIONS
Tunneling beneath open water is usually more challenging
them landside operation, often with a higher
degree of uncertainty and risk. The following lessons
of general relevancy for the planning of future projects
are applicable.
• The extent of ground investigation and planning
should always reflect the complexity of the geology,
the type of project, and the degree of risk.
• Risk assessment should start in the planning phase
and carry on in design and construction.
• The results from the investigations should be properly
documented and their use in calculations and
assessments shown.
• The geological setting and understanding of the
tectonic are vital for all large tunnel projects.
• Ground investigations where the extent is based on
bidding, may cause vital information to be lost, and
should never be accepted.
• Sufficient time must be allocated for necessary
investigations and testing.
• The ground investigations should continue through
the entire construction period. Tunnel mapping and
following up should be done by experienced engineering
geologists representing owner as well as
contractor.
• Risk analysis, assessment of uncertainties and
development of mitigation measures are critical.
• The tender documents, including geological/
hydrological/hydrographic reports, should be thoroughly
prepared, with full quality control.
• An independent reference committee should be
established. For the construction period, strict
requirements should be put on the engineer’s and
contractor’s competency and qualifications.
• Planning and investigation should always carry risk
assessment forward to the detailed design and construction
phases, since residual risk remains, even
after significant and relevant site investigations.
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REFERENCES
Barthes, H., A. Bordas, D. Bouillot, M. Buzon, Ph. Dumont,
J. Fermin, J.-C. Landry, J.-P. Larive, J.-J. Morlot, L.
Szypura, Ph. Vandebrouck and B. Vielliard. 1994a. “Tunnels
– Geology”, Paper # 10486, Proceedings Institution
of Civil Engineers, Supplement to Civil Engineering, Vol.
102, Special Issue No. 1 – The Channel Tunnel, Part 3:
French Section, ICE, London.
Barthes, H., A. Bordas, D. Bouillot, M. Buzon, Ph. Dumont,
J. Fermin, J.-C. Landry, J.-P. Larive, J.-J. Morlot, L.
Szypura, Ph. Vandebrouck and B. Vielliard. 1994b. “Tunnels
– Tunnel Boring Machines”, Paper # 10489, Proceedings
Institution of Civil Engineers, Supplement to Civil
Engineering, Vol. 102, Special Issue No. 1 – The Channel
Tunnel, Part 3: French Section, ICE, London.
Blindheim O.T., Grøv E. & Nilsen B. 2005. Nordic sub
sea tunnel projects. Tunnelling and Underground Space
Technology, 20:570–580.
CEN 1997. Geotechnical design – Part 1: General rules.
European Pre-standard ENV 1997–1, Comite Europeen
de Normalisation, 123 p.
McLeary, D.D.,W. Foreman,W.H. Hansmire and E.K.H.Tong.
2001. “Hong Kong Strategic Sewage Disposal Scheme
Stage I DeepTunnels”, Proceedings Rapid Excavation and
Tunneling Conference, Society of Mining Engineerrs, pp.
487–408, Littleton, CO, USA.
Nilsen B. & Palmstrøm A. 2001. Stability and water leakage
of hard rock subsea tunnels. Proc. Int. Symp. IS-Kyoto,
2001, Balkema, pp. 497–502.
Nilsen B., Palmstrøm A. & Stille H. 1999. Quality control
of sub-sea tunnel project in complex ground conditions.
Proc. ITA World Tunnel Congress Oslo, June 199.
Balkema, pp. 137–145.
Palmstrøm A., Stille H. & Nilsen B. 2000. The Frøya tunnel
– a sub sea tunnel in complex ground conditions. Proc.
Swedish Rock Mechanics Meeting, Stockholm March
2000, BeFo, pp. 19–30.
Palmstrøm,A., Nilsen, B., Pedersen, K.B. & Grundt, L. 2003.
Optimum extent of site investigations for underground
facilities. Publ. No. 101, Directorate of Public Roads,
116 p. (in Norwegian).
Pennington, T.W., R.F. Cook, D.P. Richards, J. O’Carroll,
and T. Cleys. 2006. “A tunnel case study in risk management”,
Proceedings, NorthAmericanTunneling, Chicago,
Illinois, Taylor & Francis, London.
Richards, D.P, P. Ramond, and O. Ezzeldine. 1998. “Design
and construction of the first bored tunnel across
the Nile River”, Proceedings, ITA Congress, Tunnels
and Metropolises, Sao Paulo, Brazil, A.A. Balkema,
Rotterdam.
Varley, P., A. Darby and E. Radcliff. 1992. “Geology,
Alignment and Survey”, Paper # 9932, Proceedings Institution
of Civil Engineers, Supplement to Civil Engineering,
The Channel Tunnel, Part 1: Tunnels, ICE, London.