Viaducts may appear less spectacular and symbolic than cable-stayed bridges, but they have a completely different presence in the landscape and a much stronger relationship to the ground. They often require very advanced geological surveys. The rhythmic quality of their supports, the elegance of their deck make them a success and a handsome addition to the landscape.

Back in 1973, Greisch office was involved in the design of an enormous viaduct in Vilvoorde. Metal still dominated the design of that viaduct.

Evolving knowledge and the concern to keep costs down led Greisch office to design a series of other combined viaducts, concrete and metal, and to use innovative methods to erect them.

The use of combined structures enabled the cost of the works to be reduced, without sacrificing anything to safety or length of working life, while considerably increasing the sophistication of these large-scale structures, giving them a more elegant silhouette in the landscape. The use of original erection methods and the taking into consideration of building constraints were combined with the concern for structural continuity.

The viaducts of Sécheval (1975 - 1979), Remouchamps (1981) and Polleur (1981) established Greisch office's reputation and led the firm to successfully carry out the works on viaducts made of pre-stressed concrete at Breitfeld and Steinebruck, the first ones in Belgium to be put into position by launching. The Eau Rouge viaduct in the Hautes Fagnes (1993) has a very wide-span arch. Built on difficult soil, its foundations required many surveys and innovative solutions.

Greisch office's familiarity with all these techniques put it among the firms invited to dimension the longest and most audacious structures on the TGV railway lines in France.