Landslides are often triggered or accelerated by human activities, such as tunnel excavation, that can induce extensive damages to the undercrossed structures and infrastructures. The case-study presented and discussed in this paper concerns a huge slow landslide temporarily reactivated by the excavation of twin tunnels for the motorway crossing the Apennines between Bologna and Florence (Italy). The large amount of monitoring data collected before and during the excavation allowed a clear identification of the landslide displacement trends along with the tunnel progressing, both at the ground surface and at the deep sliding interface. The rather articulated monitoring data have been interpreted using a finite element model that seems to be capable to describe the horizontal displacement trends during all the phases of tunnel excavation.