In addition to the stations, Trevi also works on the TBM launch well, the equipment that will excavate the underground lines; one of these is under construction in the town of Chelles, north-east of Paris, on a construction site on line 16 of the metro.
This well is particularly difficult since it has a very complex geological situation: the presence of chalks in the first 30 m complicates the realization of the foundation works, which consist mainly of circular diaphragms that are 1500 mm thick, at a depth of approximately 62 m.