Adjustment of tunnel lining service life through appropriate safety factors

• Conflicts between the service life requirements in the UK and the EU are disclosed.
• One of the rare examples of probabilistic FEAs for tunnels in London is provided.
• A methodology for alignment of safety factors to a specific service life is given.
• Safety factors can be optimised when the primary lining is assumed degrading.
• A consistent life-cycle design approach for composite linings is described.

Tunnels typically comprise large scale infrastructure projects, where a demand for an increased service life is present. The most recent large scale projects in the UK come with a requirement for a service life of 120 years. At the same time, the implementation of Eurocodes is becoming standard practice, the current provisions of which cover a service life of 50 years. On the other hand, temporary structures often do not need to be designed for a service life longer than a few years only. The present paper discusses a reliability life-cycle based methodology to adjust safety factors used in the design of tunnel linings in order to reach a specified service life, i.e. a variation of the safety factors used leading to an analogous reliability level at the start of the structures lifetime, which in turn provides a modification of the expected service life duration. As discussed herein, this procedure does not conflict the Eurocode provisions (one of the most referred standards in tunnel design) but it comes in line with the safety concept indicated in Eurocode 0 “Basis of Design”.