As part of the works for the doubling of the capacity of the Metro Tolosa – Line A, the works required the extension of some underground stations. For this purpose, diaphragms by means of trench cutter have been executed. The stations involved were Fontaine Lestang (FLE), Patte d’Oie (POI) and Mermoz (MER), in full residential area. Diaphragms with a thickness of 800 mm have been executed for an overall development of 370 ml, that is a surface of 3.600 m2, reaching a maximum depth of 9,8 m. Waterproofing injections were necessary for the treatment of the contact point between the body of the station existent and the new diaphragm wall. The treatment has been executed injecting a grout mixture of micro-cement through preinstalled valved pipes (TAM).