Sagrada Familia in Barcelona, Spanien
Due to the outstanding value of Sagrada Familia and in order to safeguard the World Heritage during the construction works for the AVE tunnel in the best possible manner, an extensive and elaborated monitoring programme had to be developed and implemented. Supplementary to the executed deformation measurements that already had been carried out for one year for selected interior and exterior façade points by using electronic distance measurement techniques (Cyclops ), a redundant crack monitoring system was to be added.
It had to serve both, safeguarding issues as well as measures for the preservation of evidences during and after the passage of the tunnel boring machine (TBM). The finally executed crack monitoring system had a strong focus on selected cracks within the World Heritage parts of the apse and the Nativity façade as well as the building joint in the eastern cloister and the movement joint near the Glory Façade, which would have shown deformations in a noticeable amount firsthand. The final position of the monitoring devices was selected due to the expected direction of any deformation and/or the movement range that could occur according previous structural calculations and simulations. Furthermore boundaries from the initial construction process within the site of Sagrada Familia were considered as well as necessary securing measures to avoid impacts from visitors and/or construction works. The selected relevant structural cracks and/or building joints were to be mainly monitored with online-devices, allowing the availability of data in real-time for a continuous and immediate review and control in order to minimize the risk potential. For redundancy reasons the implemented crack monitoring system comprised of different measurement technologies and hence adapted measuring rates/frequencies. Basically three different instruments and thus different observation techniques were utilised for the initial crack monitoring:
• Fibre-optical extensometer,
• Inductive displacement transducer and
• Crack monitors.
In particular the applied fiber-optical sensors enabled the recording of dynamic data, as they emit a constant data flow without any rough discretisation, like it would occur with other techniques and in particular with manual measurements. Hence these sensors were applied foremost in closer proximity to the tunnel axis, as significant deformations would have been recordable there first hand.
During the entire passage of the TBM geotechnical and structural effects and impacts were observed, monitored and examined in detail 24 hours per day. The precise execution of the tunneling works and the extensive monitoring involving a close collabortion among all parties contributed to the safeguarding of the World Heritage of Antonio Gaudi.