The rock in the area of the channel between Malta and Gozo seems to be “geologically promising” for the excavation of a subsea tunnel in rock underneath the seabed, according to a Norwegian rock engineer.
Eivind Grøv, chief scientist and from Sintef Building and Infrastructure, said building a tunnel will take between five to 10 years, though the length of time varied between three to four years for planning and programming and another two to three for the actual construction.
Prof. Grøv, president of the Norwegian Tunnelling Society, was addressing a public meeting in Gozo on the proposal to link the two islands with a subsea tunnel. He was invited, on a three-day visit by the Gozo Business Chamber in junction with the parliamentary secretariat.
The conference room at the Grand Hotel in Mġarr, where the public dialogue took place, was packed with more than 150 people, mainly Gozitans of all ages.
Prof. Grøv insisted that if the tunnel project went ahead there had to be further investigations and much more detailed geological data collected.
He told The Times the most important requirement for excavating a subsea tunnel was the presence of hard rock.
“The rock as far as we can see looks promising. There are certain horizons in the geological stratigraphy that we should try to avoid like the blue clay horizon, but limestone is a good rock. Further investigations need to be done before you can draw any firm conclusions, of course,” he said.
Prof. Grøv would not commit to the best exit locations, should such a tunnel be built and said there was some work that had to be done to try to establish tunnel alignment.
“At this point in time I don’t think we can draw any firm conclusions where this particular tunnel should be located, but one would probably be looking at a level in the range of 100 metres below sea level, maybe even deeper, but in that range.”
The depth of the tunnel excavations will determine the location of the tunnel exits, the incline and the length of the onshore approach roads. It was important to always try to keep the entrance points as close as possible to the sea level.
Members of the audience raised the issue of safety, some asking about the perils of earthquakes and others about emergency routes, but Prof. Grøv dismissed the concerns related to seismic activities.
“It’s interesting, because if you compare how tunnels behave in case of earthquakes, the experience suggests that actually the safest place to be would be in a tunnel. Constructions at the surface are much more prone to damage than the tunnel itself,” he said.
There would be no emergency tunnels, he said, or any sort of escape routes because these types of subsea tunnels operated on a self-rescue system.
“There is a traffic control system which directs instructions to car drivers in case of emergencies. For example it can ask them to turn round and exit the tunnel, so that the entrance can be closed.”
He explained that there would be dedicated niches to allow cars to pull to the side, turn and go back.
Prof. Grøv said the material excavated from the tunnel could be “an asset for Malta”, and that depending on the quality of the material, “it could be recycled”. He also said the tunnel would not require daily maintenance, but cleaning “some four times a year” and regular monitoring of the operational installations, which might have to be changed every 15 years or so.
In Norway there are 30 subsea tunnels, ranging in length from 1.6km to 7.8 km. The deepest one is 287m below sea level. Due to the prevalence of avalanches, landslides and snowfalls, subsea tunnels have, over the past 30 years, been the best connection between the several islands separated from the mainland by fjords.
Prof. Grøv discussed in technical detail the main excavation methods and the support measures applied, saying that the excavation of the first 150 metres on both sides were the most prone to accidents. He also mentioned seismic and tectonic movements, water inflow and weakness in rocks as the biggest risks during the construction phase.
During the building of subsea tunnels in Norway, there had been three major accidents, but to date no tunnel project has been abandoned he said, highlighting the importance of pre-investigations to identify the geological risks.
“There will always be some risk. However, this is proven technology – tested for over 25 years. This is not rocket science at all, but careful planning, understanding and management of risk,” he said.
Last week Prof. Grøv told The Sunday Times that although putting a price tag on the tunnel was premature, similar subsea tunnels in Norway cost around €13,000 per metre. With a straight line distance between Malta and Gozo of five kilometres, this means the subsea section of the tunnel alone could cost around €65 million to build.
Parliamentary Secretary Chris Said mentioned the various possibilities of obtaining EU funds for the subsea tunnel project.