Rock Mass Characterization and Assessment of Ground Behavior for the Trikokkia Railway Tunnel (Central Greece)

Abstract

The Trikokkia Railway tunnel is a 5000 m long single tube tunnel, foreseen to be constructed along the future Kalambaka–Kozani railway line in central Greece. The tunnel alignment is crossing the Molasse formations of the meso-Hellenic trench and a design approach for the tunneling works that account for the specific properties of this formation has been adopted. Mixed modes of failure governed by rock overstressing and discontinuity controlled slides were tackled by considering both rock bulk strength and deformability properties and rock mass architecture. The ground characterization process, was performed using well established empirical rock mass characterization indices. Rock mass characterization was assisted by hand sketching of rock mass structure as well as by generating discrete fracture networks, compatible with the joint statistics of each rock mass class. The identification of different rock mass behavior types is based on metrics that compare rock mass bulk strength with in situ stress state, and in parallel on the visualization of the rock mass structure to describe and quantify structurally controlled failure modes. Both the intuitive procedure to draw rock mass structure sketches, as well as the random joint generation procedure, are found to be effective tools to identify and assess gravity driven modes of failure. The adopted process to assess rock mass behavior contributes significantly to design with confidence the tunneling and support process for tendering purposes.