In Sable d’Osticourt
Lot 3 of Lille Metro connects the stations „Petite Chapelle“ and „Maison des Enfants” over a length of 3,540 m. The tunnel tube, which was driven with a mixshield TBM, has an outer diameter of 7.70 m with a minimum cover of 10 m. Besides the tunnel, six stations had to be built using the top-down method. The construction works started at the beginning of 1985 and ended in spring of 1988.
The mixshield, which was developed by Wayss & Freytag and built by Herrenknecht in Schwanau, works like a hydroshield with a liquid-supported tunnel face. The pressure of the liquid is controlled by pressurized air. The cutting wheel is arranged in such a way that it can be refitted for transportation of dry material. The soil which is loosened by the cutting wheel is transported hydraulically. Despite the fact that the ground in Lille varies from soils like chalk, marl, coarse clay to sand (Sable d’Osticourt), the shield drive was carried out accurately and without problems.
The tunnel tube has a single lining consisting of 35 cm thick and 1.20 m wide concrete segments. Each ring consists of seven concrete segments, each slightly longer than 3.0 m, and one wedge-shaped keystone. To keep to the appropriate direction while driving bends to the left or right, conical rings were installed. The tolerance of each concrete segment was ± 0.5mm.