On Monday, April 18, the first mechanical digger broke ground in the Saint-Aphrodise district of Béziers. More than 10 years after the first observations of movement in the seven buildings that form the Ricciotti block, demolition began under OSMOS's surveillance.
A sensitive worksite...
The demolition of the Ricciotti block, built on backfill in which a cesspit eventually formed, involved the State, the Departmental Council, the Metro area and the City of Béziers, with a budget of €535,000.
In addition to demolition, asbestos removal and clearing operations, the proximity of other apartment buildings required the implementation of systems to secure the demolition site, as well as the surrounding housing.
... for which every risk is anticipated
Protective rubber mats, held in place by a tail crane, were installed to prevent any damage, should the buildings slated for demolition collapse. To monitor any deformations in the adjoining buildings being preserved, OSMOS installed optical cables connected to two expert acquisition stations (EASs).
Installed in the lower sections of the buildings, where the deformation variations were strongest, due to the proximity of the ground-structure interface and the spreading strain caused by the work, the optical cables provide data that can be accessed remotely and in real time.
Those data will allow OSMOS's engineers to supply monitoring reports to the project owner, for every phase in the process. By engaging with the client at every step in the project, OSMOS can confirm that each action poses no threat to the surrounding structures and can immediately signal any abnormal behavior.
Minimum instrumentation, maximum safety
With two to four optical cables per building, 12 sensors suffice to monitor the structural condition of five three- and four-story buildings.
The first monitoring phase, which occurred one month before the start of work, identified the buildings' "normal" behavior. Any deviations from that behavior would then be detected, based on a number of criteria, both quantitative (magnitude of deformations) and qualitative (reversibility of deformations). The first months of monitoring helped to reassure the project owner.
In general, observed deformations are correlated with daily thermal fluctuations and remain within a normal scale of magnitude. The next observation periods may be linked to the phasing of the work in progress, and the project owner has asked to extend monitoring for several months after the end of the work, to confirm the structures' stability.