Gibraltar Strait Fixed Link - UN/ITA workshop - Rabat April 1999
Communiqué from ITA - April 1999
ITA Executive Council decision - February 1998
Communiqué from ITA - July 1997
Communiqué from ITA - April 1997
Communiqué from ITA -April 1999
Under a bilateral agreement, Spain and Morocco, through their respective agencies S.N.E.D. and S.E.C.E.G, are jointly studying the feasibility of a fixed link across the Strait of Gibraltar, presently developed as an undersea rail tunnel.
Seeking to provide a technical forum associated with that project, three workshops on selected tunnel engineering topics have been sponsored so far by the UN and the ITA. The first of these events was the Open Session on the Gibraltar Strait Crossing (Cairo, April 1994), the second was the workshop on "Characterisation of TBMs for tunnelling in flysches" (Tarifa, February 1997).
The third workshop in the series - which in fact followed a major preparatory session held in Vienna, April 1997 - was held in Rabat on April 22-24, 1999 focusing on the challenging subject "Costing of TBM-built tunnels". The following briefly reports on this meeting, which, organised in two working sessions, gathered 35 participants and received 15 papers by experts from 9 countries.
The opening session was presided and warmly addressed by Mr El Mehdi Benzekri, Secretary General of the Moroccan Ministry of Equipment on behalf of Mr Abdelaziz Méziane, Copresident of the Strait Crossing Joint Committee. Opening addresses were also delivered by Mr José Cappel Ferrer, Director of the Transport Division of the UN Economic Commission for Europe and Prof. Alfred Haack, President of ITA.
The first working session focused on the topic of "Cost survey and study cases" was conducted by ITA past president Prof. Z. Eisenstein who presented the introductory paper and moderated the session. The introductory paper presented the current results of an ad hoc inquiry among ITA Member Nations featuring costs of long and deep TBM-bored tunnels - 142 projects from 16 countries were received - and provided a selection of cost-related statistical analyses and correlations for a group of 69 projects. It alo included expressive ranges of variation and characteristics usable as a tool for cost estimates. The session included the presentation of papers on well known projects (Channel tunnel, Storebælt, Lesotho, Guadiaro, Somport, Doukala and others) emphasizing cost-related aspects including geo-contingencies and others hazards.
The second working session dealt with the subject of "Cost modelling and risk analysis tools". It was conducted by ITA Past president Prof. S. Pelizza, who delivered a position address on the problems involved in the cost modelling approach and risk assessment techniques, and the need for such techniques in modern, sound tunnel cost engineering. A number of papers were presented, some focusing on general or selected aspects of cost modelling, and others dealing with highly comprehensive models and tools, deterministic or probabilistic, now available at progressive stages of development.
The closing session, chaired by Prof. Haack, gave the moderators the opportunity of delivering their closing remarks in which:
¥ Prof. Eisenstein emphasized the idea of combining both database and cost modelling development as complementary - and not alternative - approaches. So, he stressed the importance of the ITA recent inquiry and the interest of reviewing and extending the survey to so far not participating, tunnel-rich member countries, in an attempt to build a more reliable database on features and costs of significant tunnels, which could provide much needed statistical background as a costing tool complementary to specific, conventional or model costing methods, deterministic or not;
¥ Prof. Pelizza emphasized the need for development of model-oriented cost estimating techniques and related risk analysis, so as to provide reliable costing tools commonly acceptable to the set of players involved in large tunnel projects, i.e. the owner, the contractor, the operator, the financier and the insurer. In connection with the consideration of risk in large tunnel undertakings - especially in undersea tunnels, as Gibraltar Strait's - Prof. Pelizza referred to the major role of the pilot gallery concept, which may go well beyond the traditional geo-reconnaissance purpose, if considered from a realistic perspective of managing cost and risk.
Finally, after Mr A. Hakimi's greetings on behalf of the Moroccan Tunnelling Association (AMTES) and Mr Benzekri's farewell address, the workshop was closed by Prof. Haack, President of ITA, who stressed the interest of the seminar as a step forward to the tunnel costing approach and expressed the ITA best wishes for the continuity of these cooperative events with the UN on the Gibraltar Strait's Crossing project.
In the next future, the full text of all presentations of the sessions, as well as the content of all discussions, will be published by the 2 societies in a single volume, which will be made available to all interested. Further information on this publication will follow in TRIBUNE when available.
ITA Executive Council decision - February 1998
The Executive Council set up the inquiry on tunnels construction costs. This inquiry has been sent to Member Nations in February. The results will be the basis for the forum to be held next fall.
Communiqué from ITA - July 1997
Under a bilateral agreement, Spain and Morocco, through their respective agencies S.E.C.E.G. and S.N.E.D., are jointly studying the feasibility of a fixed link across the Straits of Gibraltar, presently developed as undersea railway tunnel.
The United Nations, through a resolution of their Economic and Social Council, have invited relevant organisations affiliated with the UN to participate in the studies. Under consultative status with the United Nations Economic and Social Council, the International Tunnelling Association (ITA) has been directly asked to cooperate with the two government organisations S.E.C.E.G and S.N.E.D. to prepare several international workshops linked to the project.
The first of these workshops, devoted to "Characterisation of TBM for tunnelling in the flysh", has been held in Tarifa, Spain, on February 20-22, 1997, and was duly accepted as a constructive step towards a stage of full technical feasibility.
The second workshop, devoted to "Methodology to establish the construction costs of tunnels bored with TBMs" has been held in Vienna, Austria, on April 11, 1997, with a number of invited specialist organisations. The participation included also several representatives of the two governmental associations, a number of ITA's Executive Council members and Working Groups Animateurs, and international experts in the area of tunnelling. A special message of encouragement was sent by Mr J. Capel Ferrer, Director of the transport division of the Economic Commission for Europe at the United Nations, recalling the fruitful cooperation on the project, established between the United Nations Economic and Social Council, the Spanish and Moroccan Governments, the ITA and the international technical and scientific community. He confirmed he was strongly convinced that the results of the workshop would be an important step in defining the methodology to assess the construction costs.
Although the type of the TBM will significantly influence the cost, it was agreed that there should be no repetition of the previous workshop, which dealt directly with this subject, and this part of the discussion should be avoided as much as possible. The same applied to the evident need for permanent investigation ahead of the TBM, although this is an important element of costs. In his introductory presentation, R.J. ROBBINS stressed the importance of
1) keeping the tunnelling system as simple as possible, compatible with the geological conditions, due to the great depth and the potential risk for high pressure water and squeezing ground and
2) a good capability of grouting in its various forms. A significant point of discussion was the need of a pilot tunnel and, if yes, the determination of its geometric characteristics. In this regard, several views were stressed. Firstly, the main objectives of a pilot tunnel are targeted towards:
a) the knowledge of the characteristics of the ground to be encountered and the better understanding of some remaining geological uncertainties,
b) the reduction of costs of running tunnels and cross passages to be excavated later on through the lowering of geo-risks and the improvement of design thanks to a more accurate knowledge of the ground, for example by minimising lining and separation between the pilot and running tunnels, and by adopting constructional approaches based on the use of the pilot as a construction facility,
c) the use of the pilot tunnel, in operating phase, as a permanent service (and safety) tunnel, especially in the case there should be only one running tunnel (in a first stage). These three objectives all imply that the pilot tunnel should be located as close as possible to the running tunnel(s).
Secondly, the objective a) can be limited, to a certain extent, to that portion of the project route where special difficulties or uncertainities are expected. However, the fact that this possibility does not conform well with objectives b) & c) seems to deny the idea, especially in long, deep and undersea tunnel where off-shore shafts are rather impraticable. Thirdly, planning strategy or project financing have not allowed until now to wait, in any project, for the full completion of the pilot tunnel before starting the construction of the running tunnel(s). Fourthly, neither studies nor experience exist in the use of a small diameter (pilot) tunnel as a running tunnel, for trains transporting passengers and/or goods. J.M. Demorieux gave, from his own experience in the Channel tunnel, a significant amount of information about:
1) the possible ways of breakdown of the costs of the works and other activities in several elements (sections, structures É),
2) the cost monitoring systems which were used for the Channel tunnel and
3) their application, showing, as an example, that the construction equipment and the real construction costs of the 3 tunnels together represent 23% of the total investment, which is less than half of the total cost.
There was a general agreement on the schematic definition proposal presented by Z. Eisenstein that the overall cost of a bored tunnel is the sum of three elements namely:
1) a fixed part (equipment and plant costs, etc.),
2) a part depending (not necessarily in a totally linear way) on the length of the tunnel to be bored (cost of excavation, hauling, lining, etc.),
3) a part depending (not necessarily in a totally linear way) on the duration of construction (wages, rentals, interests, etc.). Moreover, as, for a well-defined machine, and without special incidents, advancement is depending (not necessarily in a totally linear way) on the time, overall cost could in a general way be expressed in a (not perfect linear) function of length.
The 3 parameters related to fixed costs, length and time vary of course from one case to another, including the fact that the first realised tunnel is always (much) more expensive than the following one(s). Nevertheless, they provide a convenient starting point for any cost analysis.
Going in the same direction, S. Pelizza presented cost diagrams showing a same linear structure, not only for cost estimations at the feasibility and tender design levels but also for cost monitoring aided with feed back information from the construction process. It was further shown that, going into details with a number of well-described technical risks, these risks can be quantified with their sizes quantifying the impact of taking more or less risks for various activities at the various stages. Variations are in the range of 10%, both for time and costs.
Finally, a short discussion highlighted the possibility of financing the Gibraltar project, and the structure of the contracts (tendering, BOT after negotiation, etc.). It was concluded that, at the moment, it seems that:
- there is still a need to provide key elements to consolidate, at the level of some national and international authorities, the feasibility of the project, especially with regard to the confirmation inferred through an appropriate, and recently started, offshore drilling programme
- current evaluations show that a pure BOT approach seems to remain quite problematic, and that a partial financing would be needed, either specifically for the pilot tunnel, or for the whole project. A provided free of charge (thus financed by public funds) undersea pilot tunnel to the BOT operator would free this operator from a large part of the geo-risks
- the rate of return, in global economical terms, for the whole project has been calculated at 13% but increases to 18% if the risks could be eliminated by the construction of the pilot tunnel financed by other means
- there is a need for optimisation research about the length (location) and cross section of the pilot tunnel, of which the role appears not only functional, but also strategic, in its links with the institutional and financial feasibility
- the technical uncertainties on the project do not exceed those on other project of the same size.
As a main conclusion, after the 2 workshops organised by the two national organisations in collaboration with ITA, it was felt that they constituted a significant way of making progress both from the technical (definition of the TBM) and financial (methods for cost estimate) points of view.
Although only two workshops were scheduled in the initial cooperation contract, it was generally felt that other areas would be worth to be discussed in similar future workshops.
Communiqué from ITA - April 1997
Under a bilateral agreement, Spain and Morocco, through their respective agencies SECEG and SNED, are jointly studying the feasibility of a fixed link across the strait of Gibraltar, presently developed as subsea railway tunnel. The United Nations, through a resolution of their Economic and Social Council, have invited relevant organisations affiliated with the UN system to participate in the studies. The International Tunnelling Association (ITA) being in consultative status with the United Nations Economic and Social Council has been directly asked to cooperate with the two government organisations, SECEG and SNED, in preparation of several international workshops linked to the project.
The first of these workshops, devoted to "Characterisation of Tunnel Boring Machines for Tunnelling in Flysch", has been held in Tarifa, Spain, on February 20-22, 1997, with approximately 40 special invited guests. The participants included Mr. J. Capel Ferrer from the United Nations Economic Commission for Europe, several representatives of the two government organisations, a number of ITA Executive Council members and international experts in the area of tunnelling, as well as representatives of machine manufacturers. The workshop has been divided in several conference sessions and activities. Important parts of the workshop have been the field visits to the sites of the three large scale in-situ experiments: the Bolonia and Malabata experimental shafts and the Tarifa experimental tunnel.
The conference started with an opening speech of Mr. Capel Ferrer, who welcame the fruitful cooperation on the project established between UN-Economic and Social Council, the Moroccan and Spanish governments, ITA and the international technical and scientific community. He expressed his high conviction on the results of the workshop which would remarkably contribute to outline the characteristics of TBM for tunnelling in flysch.
A general presentation by SECEG and SNED followed. It dealt with the geological and geotechnical aspects of the project, and was based on the fundamental and positive results of numerous studies and investigations already carried out, and on new investigation, including deep drilling at the bottom of the straits to explore the flysch formation, which started at the time of the workshop.
The three TBM-devoted sessions were introduced by a presentation prepared and delivered by one of the invited experts: Prof. Z. D. Eisenstein about "Geotechnical Criteria for Tunnel Design and TBM Selection"; Mr. J. R. Foster on "Characterisation of flysch-adapted TBM" and Prof. M. Panet on "Geoauscultation from the TBM and the tunnel". A long, lively and profitable discussion, managed by ITA representatives, concluded each session. The participants discussed the geological and geotechnical aspects of the flysch formation and their relevance for tunnel design and machine selection, the expected convergences of the excavated tunnel, the role of the overburden and the expected lining loads, pointing out that the design and construction of the tunnel is governed by the softer, clay-like "Almarchal" formation and, in the harder rock, by the possible existence of hydraulic connections between the tunnel elevation and the seabed.
Afterwards, important aspects of Tunnel Boring Machines design philosophy were discussed for the Gibraltar strait tunnel, based on a number of arguments for the detailed selection of the capabilities of the machines, and on differing view on a number of technical details and options. Finally, the available possibilities were reviewed of acquiring information about the behaviour of flysch excavated from the first tunnel - the reconnaissance gallery - with the aim of applying this information later to the construction of the larger main tunnels.
The invited speakers and experts participating in the discussion agreed that several generally accepted features emerged. Among them is the preference of a TBM over other tunnelling methods, keeping in mind the heterogeneity of the rock mass, the weakness and behaviour of the flysch's clay content and the possibility of the occasional occurence of water pressure.
Even more important has been the fact that, during these thorough discussions, no factors have been identified which could affect negatively this project from a technical point of view. The workshop has recognised the ongoing efforts to verify several assumptions and hypotheses, which are plausible and likely to be found correct. Among them are the characteristics of the flysch formation across the strait and the amount of clays with stiffness below certain level. The workshop supported these investigations, and the idea of the two strait crossing organisations to build a first gallery specially devoted to a detailed in-situ investigation appears a good tool for concluding the final design studies.
So it was felt that the Gibraltar tunnel project has made most significant progress recently and is possibly rapidly approaching a stage of full feasibility.
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