Two thrusts from a single entry shaft to build a collector
In Beaumont, as part of a project to install junctions to the Pourliat stormwater basin drain, Clermont Auvergne Métropole (CAM) called on SADE Special Works and the Poitiers-Metz RD (Clermont-Ferrand Agency), to create a stormwater collector using microtunnelling (1,200mm-diameter) along 635m.
The works
Works were executed:
- In two thrusts: the first along a straight distance of 240m and the second along 395m with a 200m bend of 400m radius
- from a single entry shaft to two exit shafts.
Using standard techniques, SADE Special Works carried out the excavation works to 3 shafts (5m and 7m-diameter), built in secant piling by an external company at depths of 5m to 8.5m.
The technique
Microtunnelling was the technique chosen for this project. In detail, one of the two thrusts was launched with short 1.5m-long tubes (instead of 3m), under the Clermont-Ferrand motorway.
In compliance with the CAM’s schedule and given the clay-rich soil on the site, thrusting was carried out in two shifts (6am-10pm), to maintain a progress rate of 10m per day.
Placed in its entry shaft last March, the microtunnel boring machine ‘Ondine’ (after the water genies of German mythology) completed its task in September 2021.
Works completion is scheduled for next December, with the creation of junctions by the Clermont-Ferrand teams.