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).

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 paper presents the numerical interpretation of a recent experiment on a real-scale levee physical model, in order to investigate the process of Backward Erosion Piping (BEP) and validate a recently proposed finite element formulation able to model both the simultaneous processes observed in backward erosion piping, i.e. the propagation of the pipe tip and the enlargement of the conduit cross-section, as well as the time-dependent effects. In previous papers, the numerical formulation already demonstrated its ability in reproducing available experimental data of full-scale physical models of levees, e.g. for the IJkdijk and for the Delta Flume tests. In the present work, as a further validation for the aforementioned formulation, we consider the numerical interpretation of the regressive localized internal erosion observed in the newly constructed real-scale levee at the Flood Proof Holland facility test site in Delft, The Netherlands. This test was mainly focused on the experimental evaluation of the time-dependent effects typically observed in these phenomena. To this purpose the levee foundation was equipped with an effective and accurate pore water pressure monitoring system. The aforementioned formulation was considered for the numerical interpretation of the test, in view of its ability in modeling the time-dependent effects in backward erosion piping. Indeed, a good agreement between calculated and measured piezometric heads and pipe tip propagations was obtained.