Belgium, Herstal

Herstal viaducts

Three viaducts on a strategic axis

In June 2017 the BESIX teams completed work on three successive viaducts at Herstal, on the E40/A3 motorway, over a total length of 650 metres and a width of 30 metres. Lying at a strategic point linking Wallonia to the Netherlands and Germany, this section is travelled on average by more than 100,000 vehicles per day. 50 men per day working 24/7on this site enabled the teams to rehabilitate a surface of more than 21,000 m² and construct over 5,000 m² of new road deck.

Three objectives

This project to rehabilitate the Walloon infrastructure network, started in May 2014, consisted of rehabilitating (complete replacement of structures, reinforcement of beams and piles, thickening the concrete slabs and repair work on the supporting framework) and enlarging (creation of emergency stopping lanes and an acceleration/deceleration lane) of a ‘triple’ viaduct spanning successively the Albert Canal, the Chertal site and the Meuse. Three objectives were pursued: improving the durability of the structures, reducing congestion at this point of particularly high traffic density, and optimizing user safety.

Difficulty number one: keying

The keying, that is joining the two structurally separate road decks, was an arduous task for the team. The old upstream structure and the new structure needed to be be connected by a 1.5 m concrete slab. This delicate operation could be undertaken only after adjusting the levels and slopes of the two road decks. For this, some 1,000 tons of ballast were placed, so as to play with the elasticity of the existing structure and to induce the necessary corrections. Readers need to know here that a stream of heavy trucks can produce vertical deformations of up to about 25 cm! The other challenges were the coordination and logistics of the slab, as well as accessibility and navigation, given the need to keep road and canal traffic flowing at all times. For this reason the work was divided into six successive phases in order to maintain three traffic lanes operating in both directions during most of the duration of the site.

Ingenuity makes all the difference

The teams had to be doubly creative when it proved unexpectedly necessary to consolidate the approach spans. Twenty metal caissons of about 12 tonnes each ‘encapsulated’ the concrete beams of the existing structure, enabling the team - after previous loading - to take the weight off them and recover 100% of their capacity. An innovative solution allowing the necessary consolidations to be done in a minimum of time.