AbstractAs part of the German national research project “Protection of critical bridges and tunnels – SKRIBTPlus” HOCHTIEF Engineering has conducted the development and testing of a protection measure against contact detonations in tunnels. The measure consists of a two layer cladding – therefore called “Sandwich-cladding” – which is installed at the inner side of the tunnel lining. It minimizes the effects of contact detonations to the tunnel lining significantly. An unprotected tunnel lining might be seriously damaged by a contact detonation, especially if the lining thickness is relatively small. If in addition the hydrological situation comprises flowable sands and high ground water pressure, the result might be a tunnel collapse or at least a water and soil swallet.The two layered “Sandwich-cladding” is build up as a precast concrete segment. The outer layer consists of micro-reinforced high-strength concrete which is known as DUCON (DUctile CONcrete). Between the outer layer and the proper tunnel lining the inner layer is placed, consisting of extremely compressible concrete. Both layers are poured as precast concrete segments, connected by reinforcement bars and then fixed to the tunnel lining using dowels and screwsThe effectiveness of the measure has been assessed in a series of blasting tests. Different materials as well as various combinations of layer thickness were tested. In order to get quantifiable results, the damaged specimens also have been subject to a load bearing test. Based on the results of these tests, in particular the remaining load bearing capacity after damage, the effectiveness of the “Sandwich-cladding” could be demonstrated and verified. In addition this was underlined by the results of numerical simulations of the test procedure.The “Sandwich-cladding” also functions as a fire protection measure, as it protects the tunnel lining from overheating and spalling. This has been assessed and verified in real scale fire-tests.