New streetcar line in Liege: West Flemish foundation specialist collaborates on Walloon mobility

Votquenne Foundations, part of the 2Fund group, was founded in 2006 by ir. Bart Cloet and grew into a fixture and a leading player in mechanical foundation and shoring techniques. Sister company Votquenne, on the other hand, focuses on manual foundation techniques. Votquenne Foundations has over 45 employees and has its own transport company, VQ Logistics, and a department for soil testing, quality control, probing and drilling, Revyson. They are currently involved in the construction of a new streetcar line in downtown Liege.

Substantial project

In 2019, the Temporary Association SM Colas Tram de Liège launched the construction of the 12 km long tramway line, which has about 20 stops. This is a new structuring and public transport axis through the city center. In addition to the construction of the track, the access pits to the sewers will also be addressed.

Drilling around an existing sewer line in service

There was an old brick-built sewer under the section. This should be preserved. Also, the old street (about 10 m wide) is flanked on both sides by old and historically valuable buildings. Due to the construction of the tracks, the existing access and inspection manholes of the sewer system can no longer be used and new ones will be realized, nine of them using machine shoring techniques. Votquenne Foundations was approached to perform these shoring works. Currently, five have already been realized, three more are planned later this year and the last one is coming next spring.

Chosen for secant pile walls with brace frames

A number of challenges also presented themselves. The subgrade was not optimal in terms of stability, due to soil layers formed by silt deposits, and the old cobblestone road surface was still present 1 m below the existing road surface. It also turned out that certain utility lines were not located where they should be. Precisely because of this subsoil, to prevent soil from sinking into the construction pits and to protect the old buildings as much as possible, Votquenne Foundations decided to work with secant pile walls. This shoring was also necessary because of the depth of the access pits.

Piles about 10 m long were provided, in diameters of 530 and 630 mm. The excavation depth varied from well to well and went up to as much as 8 m. To ensure sufficient horizontal stability, up to three shoring frames were sometimes required. To minimize the impact on the environment, anchors were also not used in order to avoid drilling under the existing houses. An additional advantage of a strut frame over an anchor row is that the curing time (required for anchors) is eliminated, which benefits planning.

Coordination and planning essential

Ludovic Huysentruyt, project manager on behalf of Votquenne Foundations: "In this project we were able to show all our flexibility, reactivity and solution orientation. For various reasons, we had to be able to react quickly and be inventive. For example, in function of maintaining mobility, not all pits could be constructed at once and we had to work in phases. For example, both sides of the road had to remain accessible to pedestrians as much as possible and the houses had to remain accessible to the fire department at all times. Coordination and planning were essential here. In addition, accessibility in the middle of the city was not always easy and space was limited. Getting machines and equipment on site was quite a challenge in itself. Finally, we also made every effort to ensure the safety of the people, as well as the stability of the surrounding homes."