Design criteria and construction techniques are briefly reviewed to present the state of the art in modern tunneling methods. The topics outlined below are discussed, with continuous reference to representative case histories.
- Classifications of tunnels (based on function or structure).
- Observed features of ground response to tunnel excavation (convergence, induced subsidence, face and support stability, water inflow).
- Major concerns in tunnel design (geotechnical and structural limit states in terms of stresses and deformations).
- Simplified interpretations of ground response (stress/strain state induced by a circular tunnel in a homogeneous and isotropic infinite medium, the "volume loss" concept).
- "Conventional" construction techniques (drill and blast, mechanic excavation tools, excavation stages, temporary and permanent supports, drainage and waterproofing).
- Ground improvement and other support techniques (radial bolts, face nails, grouting, pipe and jet grouting "umbrellas").
- "Mechanized" construction techniques (Tunnel Boring Machines, Slurry Shields, Earth Pressure Balance Shields).
- Prediction of lining stresses and convergences, subsidence and stability assessment (empirical, analytical and numerical methods).
Carlo Callari, University of Molise (Italy)