Moreover, the vibrations linked to the tunnel boring machine going past and the repetition of trains going past in the underground could cause vibrations detrimental to the stability of the Cathedral’s structures.
In conclusion, the 32 COM 7B.108 decision asked « the State Party to halt the construction of the tunnel section in the vicinity of the Sagrada Familia Cathedral and to consider changing the route of the proposed high-speed train tunnel, so as to avoid any potential adverse impact on the structural stability of the Cathedral » and to provide « a detailed report on the measures taken to ensure the protection of the World Heritage property ».
Decision 33 COM 7B.121 has taken the report of the State Party into account, which describes in detail the technical measures taken for the tunnel construction, aiming to safeguard the integrity of the Cathedral. The main decisions and technical measures taken are listed hereunder:
The State Party does not envisage changing the train tunnel tracing in the vicinity of the Sagrada Familia nor in Casa Milà’s, because of the angular impossibilities linked to the area’s viary network. Indeed, the law does not allow the excavation of a tunnel under existing buildings for security reasons and any re-routing of the train tunnel tracing would have induced excessive acuteness, unsuited to rail traffic;
In order to completely minimize the subsidence’s risk at the level of the foundations of the south-east cathedral door, the State Party plans the implantation of a bored pile wall made out of reinforced concrete, 44 meters deep and 1, 5 meters diameter, between the border of the calle Mallorca and the Sagrada Familia. It is planned that this bored pile wall will be situated between the Cathedral’s foundations and the train tunnel, 1,90 meters away from the fist, and 0,8 meters from the edge of the latter. The line of piles is 233 meters long, jutting out quite widely from the cathedral, on both sides. The piles are joined at the head with a reinforced concrete assemblage, close to the surface in order to secure its cohesion. There is a 50 cm space between the piles;
Borings and geological studies have been undertaken, showing, in depth, the presence of a soil which is in principle suited to react correctly when the tunnel’s excavation takes place. Furthermore, an ‘Earth Pressure Balance’ (EPB) type tunnel boring machine has been chosen. It has a low rotation speed and a boring technology which should make the effects of transmitted vibrations insignificant during the tunnel’s excavation;
A hydrogeological study was carried out, in order to check that the bored pile wall is not causing a water retention effect at water table level;
A ground supervision plan has been proposed, to monitor the vibrations’ parameters and movements during the tunnel excavating in order to make sure they are in accordance with the previsions, fully compatible with the conservation of the Sagrada Familia;
The railway systems will be mounted on blocs, which reduce vibrations. The speed of the trains will automatically be limited by the close presence of curves, imposed by the surface of viary network;
In conclusion, the report aims to technically prove that the train tunnel project, its specific measures, the chosen earth boring technology and the trains going past will not induce any adverse effect to Sagrada Familia’s structure. The report indicates that all experts consulted confirmed the technical feasibility of the proposed solution.
Following the receipt of important additional technical documentation provided by the State Party during winter 2009-2010, following the reactive monitoring mission of 6-11 February
State of conservation of World Heritage properties inscribed on the World Heritage List
WHC-10/34.COM/7B.Add, p. 176