Tunnelling in sulphate claystones

The paper reviews first the performance of some tunnels built in gypsiferous-anhydritic rocks, especially in Central Europe. Then, a description of the main gypsum-laden lithological rock units in Spain is made as an introduction for a description of the conditions found in a number of recently built tunnels in Spain, most of them associated with the construction of high speed railway infrastructure. Some features associated with observed heave (presence ofwater, tectonics, high sulphate content of naturalwater) have been isolated.Adiscussion of the mechanisms leading to field expansion is then made. The classical theory of anhydrite-gypsum transformation is replaced by a mechanism of crystal growth when natural water reaches a condition of supersaturation. Field evidence in support of this interpretation is given by the detailed analysis of Lilla Tunnel, located in Tarragona, Spain, which has experienced severe heave problems immediately after excavation