Parametric study of displacements on sequential and full-face tunnel excavation

When constructing tunnels with low overburden in built-up areas face stability and in the unsupported span, as well as displacements of ground and subsidence are major issues. Presently two different concepts to deal with such tunnels can be observed. One concept is to subdivide the face into several excavation steps, like top heading bench and invert excavation with a certain distance between the single steps. The other concept is a full-face excavation with a quick ring closure and heavy support of the face to account for the face stability problem. The different concepts have been compared in a parametric study, using the code FLAC3D.