An enlargement of a tunnel and method of widening a tunnel

The present invention relates to a device and a method of enlarging a tunnel of a former inner template bounded by an old vault tunnel with a new internal gauge according to which consolidation plates (12, 13) movable in the direction axial are present on a new inner template, said plates consolidating the old tunnel vault in a disassembly zone to prevent it from detaching prematurely and undesirably during operation temporarily on one channel or on two channels. This provides an effective enlargement.