Advanced foundation techniques: RTBF Média Square rests on 800 reinforced and anchored foundation piles

Franki Foundations, headquartered in Saintes, specializes in pile foundations, retaining walls and soil improvement. Its range of pile foundations includes soil displacement piles (vibration-free or driven), vibration-free screw piles with soil extraction, bored piles and micro-piles. Franki Foundations' expertise in retaining walls covers diaphragm walls, nailed walls, tangent or secant pile walls and soilmix walls.

Franki Foundations is part of the Belgian international BESIX Group and has its own offices in several European countries. In this capacity and because of its many years of experience in building pits in limited urban spaces, the company was called in for the foundation works for the construction of RTBF Média Square, the new headquarters of the French-language broadcaster in Belgium.

Challenging conditions

Due to the complexity of the project and the specific local soil conditions, various foundation techniques were used to realize the construction pit. Project Manager Olivier Vancoppenolle describes it as follows: "The terrain on which we had to work was not flat at all and showed a height difference of no less than 6 meters. This forced us to work from various platforms at different heights."

"The soil conditions also presented us with the necessary challenges. After all, we were dealing here with a typical unsaturated sandy soil, typical of the Brussels region. Because of this soil, we had to ensure the necessary stabilization when realizing the three underground levels. We achieved this by working with bent auger piles (double rotation system). One out of every two of these piles, with a diameter of 63 cm and lengths of 7 to 18 m was equipped with reinforcement, placed after concreting. A total of 800 such piles were installed over a construction pit perimeter of 450 running meters."

Complex techniques

Vancoppenolle: "By applying this foundation technique, with the resulting stabilization of the subsoil, the basement floors could be realized without resorting to the usual slopes. Because of the depth of the excavations, additional anchoring of the piles was required from a certain height. This active anchoring with prestressing cables allowed the three underground levels to be stabilized beforehand and excavated afterwards without any problems. In addition to the realization of the construction pit wall, 52 stabilizing piles and 35 stand-alone piles were realized over a smaller perimeter, some of which served as foundation piles for the tower cranes."

Phased approach

"The foundation works on this large site ran, perfectly phased, from September 2020 to February 2021, including a short downtime due to administrative reasons. The well-planned phasing of the works meant that even while we were working, the other construction partners were able to keep working without useless abandonment. Two foundation machines were continuously at work on site and over 4,500 cubic meters of concrete and 550 tons of rebar were processed for the foundation piles."