A technically challenging project
following the collapse of a 19th-century underground structure in Valenciennes.
In early September 2021, the Valenciennes Métropole Local Authority (CAVM) made an urgent call to SADE Special Works. The vault of a 19th-century gallery, located under Place de l’Esplanade in Valenciennes, partially collapsed following road redevelopment works. This gallery channels the Grand Bruille underground river.
A key facility for the CAVM, the recommissioning of the whole square had to be executed urgently: the road works were scheduled to resume in mid-October on the collapsed portion, and reinforcement works to the structure had to be completed by 15 December 2021.
A sizeable challenge for the SADE Group!
After an initial visit to the site, on 9 September 2021, to determine the type of work required, lead time and estimated cost of the various solutions, the SADE Group rapidly proceeded to a 3D mapping of the facility, in addition to execution and structural designs.
This rapid response was enabled thanks to the synergy between all players, work phases, engineers and suppliers:
- SADE Engineering was responsible for sizing the TH arch shoring and inspections
- Ségic Engineering was responsible for surveying, recommendations and sizing of the GRP liner and inspections
- HPS supplied the made-to-measure mould and GRP liners
As of 4 October 2021, the SADE Special Works teams secured the opening of the collapsed portion and transformed it into a manhole. They then shored 46m of the gallery with TH21/58.
Two subsidiaries of the SADE Group, PERRIER for the micropiles and GECITEC for the traffic load repair platform, intervened to reinforce the gallery on Boulevard Beauneveu, using a distribution slab.
SADE Special Works devoted two months to structural reinforcements along 46m of the gallery, measuring 2.2m to 2.5m high and 4m wide. Works included the reprofiling of the apron, the laying of slide rails, fitting of the specially designed GRP liners, and concrete filling of the annular gap (180m3). For the hydraulic aspect, lastly, up- and downstream tanking was resumed to accompany the changes to gallery sections.
Works were executed in a specific context: in the middle of roadworks, during the COVID pandemic and with incompressible supply deadlines.
Despite these constraints, the challenge was met with brio by the teams who were congratulated by CAVM’s heads and elected representatives for the quality of the works and more especially their compliance with lead times.