Principal geotechnical difficulties likely to be encountered when driving a tunnel through a fault zone are: instability of the face; excessive overbreak and deformation from squeezing and/or swelling fault rocks; instability of intermediate construction stages and, excessive water inflow frequently associated with flowing ground (RIEDMÜLLER, 1997).
To illustrate the influence of faults on tunnelling, we present three case studies from recent tunnel headings in the Austrian Alps. The tunnels described in this paper form part of the Austrian high speed railway system.