Montauban (Tarn-et-Garonne). Among all the cathedrals that dot the territory, that of Montauban occupies a special place. The classic-style building, owned by the State, was closed for six years before its first reinforcement work began. A long parenthesis imposed by security requirements. “In October 2020, cracks appeared in three bays of the nave, particularly between the western massif and the nave. Quite large, crossing cracks, which were the symptom of a movement of the western massif and a separation of the elements”, explains Stéphane Tissier, head of department at Oppic (operator of heritage and cultural real estate projects), which is responsible for project management of the site.
But what is the cause of these sudden cracks? The issue is all the more sensitive as the damage appeared during the construction of a five-level underground car park, near the cathedral. To achieve it, it was necessary to dig up to 18 meters deep at the foot of the building. A procedure was therefore initiated to determine whether there was indeed a causal link. “The preliminary report drawn up on March 14, 2022 by the expert concludes that the disorders observed are partly attributable to omissions and errors committed during the design phase by the company Géotec (the geotechnical design office intervened during the design),” reported the Toulouse administrative court of appeal.
The report submitted in 2023 concludes that there is a need to carry out major stabilization and support work. As soon as the cracks appeared, dozens of plaster witnesses were installed to check whether the damage had stabilized or was still active. This was followed by monitoring using sensors and crack gauges, before an in-depth structural diagnosis was entrusted to the chief architect of Historic Monuments Pierre-Yves Caillault, project manager of the operation. “It is a complex project in terms of both design and execution. We therefore had to take the time, be sure that we stabilized the studies and secured the technical choices in order to be able to resume the work in the best conditions. explains Stéphane Tissier.
The start has now been given for this 13.1 million euro project, financed by the State. Scheduled for early 2027, the first phase will focus on strengthening the structures, which should make it possible to partially reopen the cathedral in early 2028. “The principle retained is to recreate fixed points to stabilize the structure. This involves the installation of micropiles under the western massif, explains the Oppic engineer. Secondly, it will be a matter of repairing the cracks, consolidating and restoring the decorations of the chapels which date from the 18th century.e and XIXe centuries…” A second phase which should be completed by early 2029 at the latest.
