This chapter is devoted to the presentation of the most popular approaches employed to design mitigation measures. Initially, the mitigation measures necessary for a safe excavation and a permanent cavity stabilization are considered. Subsequently, the observational method, a design procedure aimed at optimizing the management of the unavoidable geological and geotechnical uncertainties affecting both tunnel design and construction, is presented. Finally, the long-term tunnel performance under accidental loads is discussed.

This chapter is dedicated to the presentation of the most popular methods of analysis employed to solve geotechnical boundary value problems, with special emphasis on the assessment of the potential hazards related to tunnelling. In particular, in Section 9.1, the general framework is outlined with reference to numerical solutions of coupled hydro-thermo-chemo-mechanical boundary value problems. In Section 9.2, the excavation phase is considered by analysing the response of the soil/rock mass close to the tunnel (‘near field’), whereas in Section 9.3, far-field tunnelling-induced modifications in stress and deformation fields and, if relevant, in the pore pressure distribution during the construction are considered. These analyses are instrumental in the assessment of the tunnel stability and in the design of the primary and final linings. Specific emphasis is given to some particularly demanding situations for tunnel construction and performance (i.e. rock burst phenomena, swelling or squeezing behaviour of the rock mass, etc.) requiring non-standard approaches to be implemented. Lastly, in Section 9.4, long-term system response is analysed. The accent is put on: (i) delayed/evolving with time strain and stress distributions (viscous and hydro-chemical effects, Section 9.4.1–9.4.3), (ii) seismic perturbations, (iii) gravitational and tectonic movements (landslides and faults) and (iv) thermal loading (fire in tunnel).