Strukton and Gubbels realize foundation for high-voltage substation Tilburg

The new 380 kV high-voltage substation near Tilburg is rising on an unusual site: partly on a former wasteland and partly on the effluent area of the sewage treatment plant. In order to build here, sites had to be relocated, dikes modified and contaminated soil processed safely. Strukton Wegen & Beton and Gubbels Infra & Milieu joined forces in this complex project. Their joint task: laying the foundations for the station, both literally and figuratively. Christian Rebbens (Gubbels), Twan van Erp and Sjaak Gerritsen (Strukton) tell us all about it.

From the tender together

The cooperation between Strukton and Gubbels began as early as the tender phase. “We know each other from previous projects,” says Christian Rebbens, general manager of Gubbels. “When Strukton asked us to participate in the tender, we decided to take it on together.” Taking on and performing the work in combination proved to be the right choice. 

Within that combination, Gubbels and Strukton were given a place on the steering committee for project supervision. “That way we kept short lines of communication and were able to make decisions quickly,” says Rebbens. The division of tasks was clear: Strukton for the civil engineering work such as concrete, dams, culverts and mast foundations, and Gubbels as a specialized earthmoving and remediation partner.

Technical manager Twan van Erp of Strukton was also involved from the very beginning. “We were already closely involved in the planning and execution strategy during the tender phase. From then on it was a three-legged team: Strukton, Gubbels and the client. Together we always looked at how we could make this complex work feasible and safe.”

Site preparation and remediation

The work site of some 35 acres had to be completely prepared for construction. This meant large-scale earthmoving, remediation and the construction of new water structures. A total of 191,000 m3 of soil was excavated and processed under remediation conditions, and 91,000 m3 of clean soil was brought in to make the site suitable. In addition, 36,900 m3 of dredged material was removed and disposed of from waterways.

“The special thing here was that we were dealing with a legacy from the past,” says Rebbens. “The soil and waterways were contaminated in many places. In addition, the existing embankments consisted of IBC construction, so they had to be rearranged into new IBC structures. In total, we moved and rearranged 25,500 m2 of IBC embankments. This allowed us to keep most of the contaminated soil in the area, but safely and controlled.”

Effluent area as greatest challenge

The biggest challenge was in the overlap with the sewage treatment plant, which had to remain in operation during the work. “The effluent water continued to be discharged into the area during construction,” Van Erp explains. “That meant we had to install temporary sheet pile structures and later dredged and filled in the effluent pond area. That part alone required pontoons with cranes and the removal of contaminated dredged material. A huge operation, especially since we had to constantly take into account the water level.”

About 2.5 acres of the effluent area fell away to build the station. To compensate, two new water storage areas were constructed on the other side of the N261, complete with steel sheet pile walls, overflow areas and new weirs. “We realized the three large concrete tubular weirs with adjustable valves on the job,” says Van Erp. “That is millimeter work, because the water management must function perfectly.”

Civil precision and customization

In addition to soil and water, there was also a lot of focus on civil precision. Strukton realized four new mast foundations and reinforced four existing ones. “Because the pylons will soon carry the new 380 kV line, the dimensions must be right down to the millimeter,” Van Erp emphasizes. “For three foundations, we used screw injection piles and realized concrete bases above them. Each foundation was customized, because existing pylons all had different shapes and piles. That required flexibility and engineering in the work.”

That approach applied more broadly. “We were working with old objects about which little was known,” says Rebbens. “That meant researching and making choices over and over again. With the last mast foundation, we even suggested an alternative foundation method to eliminate timing risks. That proactive thinking along was received positively and shows that our risk management is in order.”

In addition, three new culverts were constructed and two existing ones extended, and a total of 1,800 m2 of asphalt was laid for the express bicycle route with two new bicycle entrances. “That route ran right through our work area,” says Rebbens. “We created a temporary detour so that cyclists could pass safely.”

Logistics, weather and risk management

Implementation required flexibility and looking ahead. “In late 2023 and early 2024, we had weeks of rain,” says Rebbens. “Despite that, deadlines had to be met. You know where the client's interest lies: making sure the station is operational on time. Then preparing the site for construction and erecting pylons are crucial. So then you start looking: how can we ensure that the mast builder and SC&M can continue? Water board and municipality of Tilburg performed a lot of work in parallel, everything had to fit together. We succeeded and we are proud of that.”

According to Gerritsen, everyone made the best effort to put the puzzle together. “Together with TenneT and Antea, we sometimes adjusted the phasing: what do you pull forward, what do you push back so everyone can continue.”

Van Erp emphasizes that anticipation was essential. “No matter how well you prepare everything, with this kind of project you are always surprised by unforeseen circumstances: nature, soil, technology. The question is: can you respond to that quickly and safely? We managed to do that together.”

Collaboration key to success

Despite the size and complexity, Strukton and Gubbels look back with satisfaction. “This project had so much common ground, with TenneT, SC&M, Antea and later Hanab/Selt that cooperation was really the key to its success,” says Gerritsen. He emphasizes the versatility: “We did everything here on one site: earth moving, remediation, weirs, mast foundations. Technically and logistically enormously challenging, but you make choices together that are in the best interest of the project. The end result is the best proof that this collaboration works.”

Rebbens adds: “TenneT facilitated that cooperation and organized regular safety boosts and coordination meetings. That kept everyone on their toes and ensured that safety remained paramount. Ultimately, the power lies in trust: knowing that the other is doing their job well so that you can continue.”

It also worked extremely well within the combination itself, according to Van Erp: “We very deliberately ‘let go’ of what was tendered in 2023. By bringing in extra people and adjusting the sequence, we secured quality and lead time.” 

The result is impressive: everything was completed within TenneT's deadline, with high-quality work and hardly any completion points. With this, the high-voltage substation will soon stand firmly on its foundation. Meanwhile, SC&M has started the construction of the substation itself, another beautiful link in the chain in which everything comes together.