This paper deals with full face excavation of large size tunnels in rock masses of very poor quality which exhibit squeezing behaviour. Time dependence is accounted for explicitly by using constitutive models which have been validated with reference to laboratory testing and in situ performance monitoring. The case study of the Saint Martin La Porte access adit (Lyon-Turin Base Tunnel) is taken as illustration. In this adit an innovative excavation-construction method is being used to cope with the severely squeezing Carboniferous zone encountered. An essential feature of this method is a two-stage excavation sequence with installation of a composite pre-reinforcement/reinforcement system with deformable elements embedded in the shotcrete lining. The tunnel response has been analysed by both semi-analytical and numerical solutions with close attention paid to the constitutive models adopted. Results of modelling are compared with convergence monitoring data.