1.         Works of Antoni Gaudí (Spain) (C 320bis)

Year of inscription on the World Heritage List  1984

Criteria  (i)(ii)(iv)

Year(s) of inscription on the List of World Heritage in Danger  N/A

Previous Committee Decisions  see page https://whc.unesco.org/en/list/320/documents/

International Assistance

Requests approved: 0
Total amount approved: USD 0
For details, see page https://whc.unesco.org/en/list/320/assistance/

UNESCO Extra-budgetary Funds


Previous monitoring missions

January 2010: Technical expert mission (ICOMOS)

Factors affecting the property identified in previous reports

Construction of a high-speed train tunnel 

Illustrative material  see page https://whc.unesco.org/en/list/320/

Conservation issues presented to the World Heritage Committee in 2010

The high-speed train line (AVE) project, Madrid-Saragossa-Barcelona-French border, resulted in the choice of planning the construction of a tunnel under the town of Barcelona. The train tunnel project goes in front of the Sagrada Familia, under the Mallorca street and in the very close vicinity of the foundations of the Cathedral’s Gloria façade. The construction of its south-east porch is not currently finished. The train tunnel also passes in front of the Casa Milà, under the Provença street. At the Sagrada Familia’s level, the diameter of the tunnel’s axis measures 12 meters and would be approximately situated 30 meters underground. The foundation piles of the cathedral are 11 to 13 meters deep.

Decision 32 COM 7B.108 took this threat into account, considering the documents and information which mainly pointed out:

a. The presence of cracks in various bordering buildings, where the train tunnel construction had already begun.

b. The World Heritage Centre and ICOMOS expressed concern regarding the possible construction of a tunnel, threatening the integrity of the Cathedral’s structure, particularly through differential displacements of the ground, greater than those planned for the Cathedral’s construction project. Furthermore, subsidences of a few centimeters had already been observed, the weight of the building causing occasional crackings in its superstructures. Therefore, it is initially a high and heavy construction, with a particular fragility. The Cathedral is currently unachieved.

c. 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.

d. 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:

a. 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;

b. 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;

c. 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;

d. 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;

e. 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;

f. 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;

g. 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 2010 and a consultation meeting held at the World Heritage Centre on 16 April 2010, the State Party confirms the essence of the technical options described in the previous point.

They are currently being carried out.

a. The tunnel boring machine is working since the month of March, from the north-east junction of the Sagrada Familia and the Casa Milà’s. It should reach the vicinity of the Sagrada Familia at the beginning of autumn and later on, the Casa Milà. It is a specific tunnel boring machine with a permanent pressure compensation mechanism, whose results have been successfully tested. A series of measures and supervision are being carried while this machine is being used, for its entire route.

b. Three independent mathematical studies, known as « with finished elements » can predict the dynamic behavior of the grounds and anticipate the subsidence’s effects or the hydrological behavior of the bored pile wall. For the project promoters, studies show the following in a categorical way: on one hand, the effects of subsidence linked to the building itself, due to its weight and on the other hand, the bored pile wall having a positive impact on the stability of the building, induced by the buttressing of its south-east side. With this existing situation, the subsidence induced by the train tunnel excavating would be insignificant;

However, less optimistic conclusions to these studies are brought forward by independent experts. They comparatively consider the results of these studies and relativize their impact in regard to the specificity and structural fragility of the Sagrada Familia and to a lesser extent that of the Casa Milà, a residential building with smaller proportions.

c. The concrete piles are practically all in place (April 2010). However, various trustworthy sources have mentioned unexpected secondary effects. At the beginning of March, during the construction works, an 80 centimeters deep breakdown in the paving in front of the cathedral was noticed; in the immediate vicinity of the bored pile wall. Furthermore, following a storm, rainwater would not have been evacuated, making the ground abnormally soft in front of the Cathedral’s south-east porch. These anomalies are considered to be surface ones and purely isolated, unrelated to implantation of the piles;

d. The hydro geological effects have been carefully compared to natural movements of the water table and its seasonal flow variations. The effects of the bored pile wall remain very much below natural variations and neither do affect the flows nor the water table's seasonal level changes;

e. A technical network for the monitoring of the static and dynamic behavior of the grounds in vicinity of the Sagrada Familia and the Casa Milà has been put in place. Four automatic stations in charge of controlling the structural shape changes of the Cathedral also guarantee its supervision. It appears that the subsidence effects linked to the building, to its construction being carried out , or to the wind, must be followed-up carefully, as well as the recording of wall cracks.

f. The State Party suggests establishing a monitoring Committee, in order to ensure the quality and supervison of construction works, including independent experts;

g. The European precautionary norms and construction supervision norms in urban zones have been respected; and beyond.

In conclusion, the World Heritage Center and ICOMOS deeply regret that a re-routing solution of the underground plan in the vicinity of the Sagrada Familia and the Casa Milà has never been seriously examined. The technical arguments of the viary network and its angles which would be to sharp in case of a re-routing seem to be denied by a simple examination of the city’s planning structure. The two streets parallel to the Mallorca street, in the south-east, the Valencia and Arago streets, offer the same angular characteristics, at the price of a slight extension of the line, in the Sagrera train station’s axis. The extension, necessary for such a shunting, indeed more expensive, did not seem like an unmanageable task.

ICOMOS considers that the works that have been undertaken and the forward-looking studies provided, in the perspective of maintaining the underground line in its plan, in the vicinity of the Sagrada Familia and the Casa Milà, provide elements which are in principle in favor of the projects’ upholding : irrelevant subsidence effects compared to those due to the actual weight of the Cathedrals’ structure, reinforcement of the Cathedrals’ foundations with the bored pile wall, irrelevant hydrological effects compared to the natural variations, a ground favorable to the tunnel driving of a relative depth with no surface damage, use of boring material and use of additional techniques with low vibratory effects, highly limited speed for rail convoys, etc. Furthermore, ICOMOS considers the implementation of a Construction Monitoring Committee, including independent experts as an element of warranty. The Committee must provide a monthly report concerning all recorded events related to the effects of the tunnel’s excavation, in any way connected to the conservation of the Cathedrals’ structural integrity. However, ICOMOS emphasizes the following points:

The suggested creation of a Committee in charge of monitoring the construction works must be implemented and its formation must be extended – in comparison to the suggestion made to date. The point of view of the critical experts for the project must absolutely be taken into account. They especially recall the structural fragility of the Sagrada Familia, which cannot tolerate any slight risk-taking. For this reason, it would be necessary to integrate within the Construction Monitoring Committee, for instance, at least a representative of the Ministry of Culture and a representative of the Property Management Authority. This Construction Monitoring Committee must particularly be in charge of:

• On a permanent basis, collecting and interpreting results of the supervision related to the process of progress of the train tunnel and existing buildings, taking into account the various ground layers along the path ;

• Creating an independent model for the examination of buildings in the vicinity of the Sagrada Familia, on the basis of monitoring outcomes ;

• Creating an independent model for the examination of buildings in the vicinity of Casa Milà, adjusting it with the outcomes of the further ground studies report and going by the monitoring results ;

• On a permanent basis, adjusting the calculation models according to the measures that have been taken and to the previsions concerning ground movements as the works progress, and take extra measures if necessary;

• Undertaking a long-term monitoring of the ground pressure increase on the tunnel, due to further constructions in the Sagrada Familia Cathedral, including a long-term monitoring of the structure originally built by Gaudi;

• Keeping the World Heritage Centre regularly updated with the outcomes.


These measures must contribute to create a permanent monitoring instrument, accepted by all members of the Building Monitoring Committee. This Committee must be able to initiate an immediate halt of the tunnel boring works, in the occurrence of proved exceeding of the physical limits, part of the global chosen indicators and examine the reasons. The Committee’s remits must concern the Sagrada Familia and the Casa Milà.

The question of possible vibration transmissions when underground trains pass must constitute a topic for a specific, precise and regular monitoring programme. This must be added to the property’s monitoring in the Management Plan, for the future high-speed train, if this itinerary is finally achieved, as well as for the metro lines 5 and 2, which pass in the immediate vicinity of the Sagrada Familia. A possible reinforcement of the vibration absorption systems inside the tunnel must be envisaged with the rail constructor. The speed of the convoys must be strictly limited.

The independent technical monitoring of the state of the ground and their possible subsidencies must be pursued after the works have been achieved, as a monitoring element of the property in its entirety, especially because of the effects due to the weight of the construction. Furthermore, the tri-dimensional monitoring models and structural analysis models of the Sagrada Familia and Casa Milà must be pursued.

The World Heritage Centre and ICOMOS recall that the inscribed property, concerning the Sagrada Familia only consists in the part of the Cathedral directly built by Gaudi. It is the crypt and the Nativity façade, which are not directly on the edge of the line of reinforced cement piles. However, it is obvious that a possible damage of some importance caused to the parts situated closely would alter the exceptional universal value of the property.

Analysis and Conclusions of the World Heritage Centre, ICOMOS and ICCROM


Decision Adopted: 34 COM 7B.98

The World Heritage Committee,

1. Having examined the document WHC-10/34.COM/7B.Add,

2. Recalling the decision 33 COM 7B.121, adopted at its 33rd session (Seville, 2009),

3. Notes that the suggestion of re-routing the fast train AVE's underground path, in the area of the Sagrada Familia and the Casa Milà, has been the subject of real studies, and acknowledges that the selected routing was the most feasible;

4. Takes note of the technical documentation provided by the State Party, about the conditions to continue carrying out the tunnel boring works currently being undertaken;

5. Urges the State Party to take the following points into consideration, in order to improve the monitoring conditions of the tunnel boring works, in the vicinity to the Sagrada Familia and the Casa Milà and their immediate halt at the slightest alert or slightest uncertainty of the grounds' behavior, in order to ensure the Sagrada Familia's and the Casa Milà's structural integrity:

a) Put the Construction Monitoring Committee in place and extend its formation in order to guarantee that it includes independent experts,

b) Clarify the technical programme related to the monitoring of the tunnel boring machine's progression to the Sagrada Familia, in relation with the finest prevision possible concerning the static and dynamic consequences on the grounds and foundations of the Gaudi buildings,

c) Confirm the scientific and administrative conditions by which the Committee can suspend, with no delay and with full authority, the tunnel boring works,

d) Put in place a monitoring programme concerning the vibrations linked to underground rail usage at the level of the Sagrada Familia, for the two existing "metro" lines as well as for the future high-speed train (AVE) underground line, and consider a possible reinforcement of the vibration absorbing devices,

e) Perpetuate the Monitoring Committee after the works have been achieved, in order to ensure a monitoring programme, concerning the grounds and modeling of the structural outcomes of the Sagrada Familia and Casa Milà, taking into account all the parameters linked to these two buildings once the works have been achieved;

6. Requests the State Party to keep the World Heritage Centre regularly updated on the establishment of the Construction Monitoring Committee and its criteria, as well as the progress of the works and the monthly conclusions of such Committee;

7. Also requests the State Party to submit to the World Heritage Centre, before 1 February 2011, a report concerning the progress made with the implementation of the recommendations, so it can be examined by the World Heritage Committee at its 35th session in 2011.