MODELLING OF TUNNELS IN SQUEEZING ROCK

This paper discusses full face excavation for large size tunnels in a rock mass of very poor quality which exhibits squeezing behaviour. The interest stems from the increasing world-wide activities in conventional tunnelling in difficult ground conditions. Following a brief review of the modern technological developments associated with full face excavation of large size tunnels, where systematic reinforcement of both the working face and of the ground ahead of the advancing tunnel is required, the attention is posed on the use of the interactive geotechnical design approach with numerical modelling and performance monitoring being systematically adopted during excavation. It is shown that numerical modelling of tunnels in squeezing rock can be performed by using a time dependent constitutive law, with a careful simulation of the tunnel excavationconstruction sequence. The case study of the Saint Martin La Porte access tunnel of the Lyon-Turin Base tunnel, in the Carboniferous Formation, is taken as illustration.