Viscoplastic models for the analysis of tunnel reinforcement in squeezing rock conditions

ABSTRACT: Numerical analyses of tunnels in rock masses which exhibit a time dependent behaviour, such as in severely squeezing conditions, require the use of viscoplastic constitutive laws. Tunnel excavation needs to be modelled with attention paid to the excavation-construction sequence, in order to correctly estimate the interaction between the rock mass and the support system. This paper presents the numerical analyses carried out to study the excavation process of the Saint Martin La Porte access adit (Lyon-Turin Base Tunnel), where very severely squeezing conditions were met. In order to face these conditions a novel construction system has been implemented, with performance monitoring being used systematically in order to closely follow the tunnel response. Two different viscoplastic constitutive models (SHELVIP and 3SC) have been adopted. A comparison between numerical results and monitoring data allows one to assess the potential of the two models