Monitoring and Urgent Interventions for a Monumental Masorny Structure due to the Thessaloniki Metro Works

The first and basic line of the Thessaloniki Metropolitan comprises almost 10 km of a twin tunnel (with a diameter of approx. 6.5 m) and a number of rather large stations, approx. every 1 km. Within the zone of influence of the metro works, certain buildings as well as monuments (mostly Roman, Byzantine and Turkish ones) have been inspected, investigated, documented and monitored, both from the geotechnical and the structural point of view, and among them the oldest and biggest Turkish Mosque of the city (Hamza Bey Cami / Alcazar), built around 1475 AD, very close to the City Hall, in the "heart" of the city, the co-capital of Greece. The deep foundation of this monument is located practically above one of the tunnels, while one of its corners is located very close to one of the corners of the near-by large metro station. Due to a lot of alterations, interventions and changes of use, combined with deterioration and damage suffered from earthquakes and fires during the centuries, the condition of this monument was bad, although a limited repair programme was under way by the Ministry of Culture; in addition, the first indications from the inspections and the conventional monitoring during the early works were alarming. Therefore, an extensive and well planned programme of investigations (of both the foundation and the superstructure) and advanced monitoring was enforced, combined with a close follow-up, calibration of data and detailed geotechnical and structural designs, while an early decision was taken, that of urgent mitigation measures and interventions (on the foundation as well as on the superstructure), which have been mostly completed. In this paper, certain aspects of the whole project are presented and discussed, together with some significant details of the monument itself (its foundation and structure), of its long-term monitoring and of the relevant designs and interventions.