Tunnel projects in Europe form a large portion of the infrastructure market, and there is continuous demand for the construction of new tunnels. Underground structures and particularly tunnels are unique structures. Their key design considerations and structural behavior are different from other structures, such as buildings and bridges, as the main bearing element in tunnels is the surrounding soils and rocks. Despite the unique characteristics of tunnel design, there are no currently available European tunnel design standards or harmonized guidelines at European level. Thus tunnel design in Europe is being carried out based on the national knowledge and experience with the use of industrial/client standards and guidelines, as well as with parts of the EN Eurocodes (EN 1990 – EN 1999). The EN Eurocodes are a set of European Standards which provide common rules for the design of buildings and other construction works to check their strength, stability and fire resistance. However, the scope of the first generation of the EN Eurocodes covers buildings and some other civil engineering works, e.g. bridges, towers, masts, chimneys, silos, tanks, pipelines. There are no parts devoted to the design of tunnels, as the Eurocodes do not include explicitly all underground structures.
The report delineates that the development of design standards for tunnels and underground structures is certainly feasible (at least for typical configurations) and that it would be advantageous to foster harmonization of design rules between countries. It appears suitable that the concept of new standards or guidelines for the design of tunnels shall be developed in line with the EN Eurocodes and delineate how to complete and/or restrict their use for tunnels without limiting the required flexibility, having in mind the specificity and diversity of tunnel design. In parallel, it would be beneficial that the concept will be consistent with the new developments in the second generation of the Eurocodes currently under development and expected to be published after 2020. Further, it is evident that there is need to (i) define what is specifically being used for tunnel design from the current Eurocodes, (ii) assess what is missing and (iii) identify what should not be used in tunnel design, keeping in mind that the Eurocodes were originally not meant for dealing with tunnels.
Sufficient literature, case studies and experience is available to prepare the general framework of a standard or guiding document, as well as addressing most common types of underground structures. Currently existing standards, guidelines and recommendations for tunnels in some European countries, as well as the Eurocodes and international codes, can serve as the basis for the development of the new standards or guidelines.