Tunnelling through varying soil conditions in north-west Greece

Tunnel S2 of the Egnatia Motorway is excavated through heavily fractured limestone and sheared sediments. Originally a fold and thrust belt was formed in the Alpine orogenic phase. Post-orogenic tectonics resulted in heavy fragmentation. The underlying material consists of clays and clayey sandy gravels. The basement of the clastic formation consists of evaporites. This variety of geological conditions resulted in considerable variability of tunnelling conditions and the need for extensive primary support measures. Owing to the mixed and rapidly changing geological conditions the type and intensity of primary support measures were selected according to geomechanical conditions at the crown. Slope stability problems were encountered during the excavation of the entrance portal, and because of the associated risk an additional study has been carried out to determine appropriate soil parameters for the excavation works through such a medium. Oedometer tests and direct shear tests were carried out to investig...