The Malta Independent 15 October 2021, Friday

Thorough geological studies to ensure safety needed for metro proposal - geologist

Kevin Schembri Orland Monday, 11 October 2021, 09:30 Last update: about 4 days ago

Thorough and detailed geological studies must be undertaken for the metro proposal to ensure safety and minimise the disturbance to residents above, geologist Peter Gatt told The Malta Independent.

The government recently published a study for a metro system on the island. The study was carried out by Arup Group, a London-based design, engineering and planning firm. The metro system as proposed will include three metro lines with a total of 35km of tracks and 25 stations across Malta's main urban area. The study suggests that the metro system will mostly be underground, with a small part of it above ground between Naxxar and Bugibba.

Writing on Facebook, Gatt said that the proposed underground (Malta Metro) is an excellent concept that would revolutionize public transport. “However, at this stage, the ARUP proposal is not based on geological studies or input to make it a realistic proposal.”

He referred to the Gozo tunnel and aired concern at the geological studies conducted for that project. “One hopes that TM’s ‘geological studies’ (if any) for the Metro will not emulate those already done by TM for the proposed Gozo tunnel, and be better,” he said.

Speaking to The Malta Independent over the proposed metro, he said that there isn’t a lot of information available yet. “What has been presented are the locations of the 25 proposed metro station.”

During the presentation announcing the metro system, Donald McDade from the ARUP Group, said that the tunnels would typically be positioned 10-12m below the surface to minimise impact on properties located above, with stations in some locations deeper.

Asked about this 10-12m, Gatt wasn't quite sure what McDade meant by it. "Are we speaking below street level? Below sea level? There has to be a datum. If it’s below sea level then that means they would need to use special equipment that would be more costly for tunneling. Or is the whole system going to be above sea level, in other words through relatively dry rock. There isn't really much information about this yet."

Gatt stressed the need for proper, professional and extensive geological studies, adding that they must be far more in-depth than the studies that were conducted for the Malta-Gozo tunnel.

"We don't know what kind of study Transport Malta will carry out for the metro, but in this case there will definitely be areas with problematic geology. There are areas where the surface geology does not give much information, but in fact underlying, there are certain geological structures which will impact any excavation."

Given that the metro would pass beneath residential areas, he was asked whether it could cause vibrations to be felt by people residing or using the buildings above. "Vibrations during excavation and even when the trains themselves are running would depend on how deep the tunnel actually is. The depth would vary from place to place depending on the land's topography." 

"An even worse effect would be if you have a tunnel collapse during the excavation phase. Such a situation could lead to a void migrating upwards to the surface creating a sink hole. This is why very detailed geological studies would be needed in advance, ones that are far better than what was done for the Gozo tunnel.”

He said that there is another aspect of the entire system. "Trains cannot really go up inclined surfaces, except for slight inclines. So the whole system has to be at, or close to, one level. We don't yet know how they are going to negotiate this and how the whole system will be excavated keeping roughly the same level. It will be difficult."

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