The ancients referred to the 9-mi. (14 km) wide Strait of Gibraltar as the Pillars of Hercules, and a project is currently under way for a Herculean task — the construction of twin subterranean railway tunnels linking Spain and Morocco.
The idea of a fixed link between the two continents dates from the 19th century, when railways became widespread as the new transport system.
Modern interest was revived in June 1979 during a meeting between King Juan Carlos I of Spain and King Hassan II of Morocco. Their agreement was formalized in October 1980 with the Accord de Cooperation Technique et Scientifique entre le Maroc et l’Espagne, signed in Marrakesh, Morocco.
The governments of Spain and Morocco have founded two companies to represent their interests: SNED (Societe Nationale d’Etude du Detroit) and SECEG (Sociedad espanola de Estudios para la Comunication fija a traves del Estrecho de Gibraltar).
Preliminary Design Under Way
The joint venture coalition comprising TYPSA, based in Madrid, Spain, Lombardi Engineering Ltd. of Minusio, Switzerland, Ingema, headquartered in Rabat, Morocco, and Geodata SPA of Turin, Italy, was awarded the contract for environmental impact studies and preliminary project design in September 2006.
TYPSA heads the joint venture and is responsible for environmental studies, while design work is being led by Lombardi Engineering. Lombardi is presently engaged in geomechanical analyses, headed by company president and technical project director Giovanni Lombardi. Ingema cooperates in the geological and environmental studies, while Geodata handles matters related to geotechnics and tunneling methods.
It is anticipated these studies will be completed by the end of 2007.
Test borings were carried out in both countries in the 1990s, said Andrea Panciera, project manager of Lombardi Engineering.
“In Spain a tunnel in Tarifa about 400 meters [1,312 ft.] long was bored with an open tunnel boring machine. A shaft in Bolonia, Spain, approximately 80 meters [262 ft.] deep and another some two meters [6.6 ft.] wide and 150 meters [492 ft.] deep in Malabata, Morocco, were also sunk,” he stated.
A system of small tunnels and testing chambers was excavated at the bottom of the Malabata shaft, as well as a tunnel giving access to a second shaft. The latter descends to 984 ft. (300 m) and leads to another short test section.
Challenges to Be Overcome
“The Gibraltar tunnels will be the deepest ever excavated under the sea, and also one of the longest at approximately 40 kilometers [25 mi.], 29 kilometers [18 mi.] of which will be under water,” Panciera noted.
Twin railway tunnels with a service/emergency tunnel are to be constructed. Underwater sections will go as deep as 1,640 ft. (500 m) and therefore present a number of extreme challenges.
At approximately 3,281 ft. (1,000 m) deep the Strait is unsuitable for the supports for a traditional bridge, and a floating span would interfere with the large amounts of shipping navigating this narrow bottleneck at the mouth of the Mediterranean. The very strong current and high waves also must be taken into account. A prefabricated underwater tunnel has been ruled out because of the unstable nature of the seabed.
“The Gibraltar tunnels can be defined as the most complicated to be designed at present for extremely complex geological and geotechnical conditions,” Panciera pointed out.
“At the lowest depth the water pore pressure is higher than the effective stress in the rock mass and the mostly marly nature of the crossed flysh formations and the soft breccia filling the two paleo-channel in the middle section of the Strait also don’t help for an ’easy’ solution.”
As a result, the inter-continental route will therefore not traverse the shortest distance between the two countries but rather the best under prevailing conditions. The tunnels will run from Punta Paloma, near Cadiz in Spain, to Cape Malabata, near Tangier in Morocco, an area where the sea is only 984 ft. (300 m) deep.
Current Stage of the Project
At this point design work is still under way.
“The geological and geotechnical aspects have been further studied and the results are the basis for the next steps. Design is now dealing with geomechanical analyses, for which the development of particular computation models is needed due to geomechanical and hydraulical conditions, which are out of the usual ranges and combinations,” said Panciera.
“The study of the building method is considering the possibilities for application of tunnel boring machines [TBM] integrated by special systems for the support of the excavation face, such as hydroshields or EPB [earth pressure balance]. Geomechanical conditions are extreme and no decisions have yet been made. They will depend also on the results of the geomechanical computations and the final design will possibly need a further investigation campaign.”
It is anticipated most of the tunnels will be excavated by earth pressure balanced shields (EPB) or other similar techniques, although the equipment to be used is not yet settled since geomechanical analyses, which form the basis for deciding equipment specifications, are still ongoing.
“In addition, geological features are present, which make the situation more complicated than it was in the previous design run,” Panciera continued, “and aspects relating to the safety of the tunnel when in service are quite different as well, due to changing national and international safety standard regulations.”
The preliminary design will need the approval of the two client companies before a decision can be taken on final design and preparation of tender documents. The project schedule also will depend on aspects other than the technical, such as governmental decisions.
Financial arrangements also will needed to be addressed, and while it is too early for a reliable cost estimate, figures suggested for construction of the tunnels have ranged from $6.5 billion to $13 billion. It appears private investors will be invited to participate and it has been reported additional funding will be sought from the European Union.
Once the tunnels are built, however, they will provide numerous benefits for both countries and continents, including increased tourism revenues, rising real estate markets, and enhanced commercial and investment opportunities — not to mention the possibility of boarding a train in the north of Scotland and disembarking in Africa. As Roger Helmer, Member of the European Parliament for the East Midlands region of the UK, stated, “This is an ambitious project and a prime example of international cooperation and endeavor, which will aid economic development in both countries.” CEG
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