The special feature of this project lies in building three underground station extensions, which required the removal of the tunnel lining, while keeping the subway in operation. One of the operation complexities was the utter necessity to limit any inconvenience for the passengers, while guaranteeing the accessibility and security requirements of an automatic operating metro. This needed to be done along with minimizing, as much as possible, the disturbance caused by the works on the very urban environment. A steel rib support lined with steel plates was placed around the tunnel during the summer 2017 and removed in summer 2018. This tunnel shell isolated the construction site from the subway in operation. This made the construction of the diaphragm walls, the excavation on both sides of the tunnel and cutting of the lining in the extension are a possible. At no time were the 220,000 passengers of the A Line aware of travelling in the heart of an underground construction site. A success that deserves to be recognized.