Input data: geotechnics

Reducing the risks associated with tunnel construction is the main purpose of geo-technical investigations and characterization. It is therefore essential that geotechni-cal investigation be carried out since the very beginning of the project. This requires collecting all existing information and data. At the same time, the relevant design parameters should be assessed from the collected data to: choose a suitable alignment for the tunnel, analyse the stability of the face, define the associated ground support and improvement, design the tunnel lining and carry out a pre-construction risk as-sessment on buildings adjacent to tunnelling works. On such basis, the geotechnical characterization should permit us to assess the feasibility of alternative schemes, to select the most appropriate construction method, to anticipate possible risks during construction and to undertake any possible mitigation. In this chapter, after recalling the main definitions of geotechnical properties, lab-oratory tests and site investigation for geotechnical characterization of tunnelling are presented and the geotechnical model is discussed.