Blending technical expertise, heritage project experience and a commitment to reducing carbon emissions, Keller is helping future-proof the historic seat of government in the Netherlands.
The project
Built primarily in the 13th century, the Binnenhof in The Hague is among the oldest parliament buildings in the world still in use.
Since 2021, the historic complex has been undergoing an extensive renovation to replace outdated installations, combat its deteriorating condition and protect the seat of Dutch democracy for generations to come.
Strengthening the foundations
Due to the size and complexity of the scheme, the work has been divided into three zones, with a main contractor and foundations company selected for each.
As one of the few companies in the Netherlands to not only offer large-scale jet grouting, but also expertise of heritage projects, Keller was chosen by main contractor Heijmans for their section.
“Our job has been to extend the existing foundations, which will strengthen them and allow the client to deepen and modernise the basements,” says Marcel Mertens, Branch Manager.
The first phase began on site in early 2024 at the Stadtholder’s Gate, which dates from 1620 and is the entrance to the Binnenhof’s inner court. But a larger portion of the work took part in 2025 and involved underpinning the foundations of the Senate house.
Working in a confined space
Operating in the confined basement with narrow doorways and little more than 2m of headroom, the crew used two small jet grouting rigs to minimise movement and carry out the carefully planned sequence of works.
“A project of this nature requires sensitivity and specialist expertise,” says Marcel. “A lot has been built and rebuilt on this site over the centuries, so there’s been considerable ground investigations to understand what’s in there and how that would impact on our design.”
One of the biggest considerations was making sure the jet grouting wouldn’t cause any settlement damage to the famous buildings. Working with a strict 3mm movement tolerance, the team reduced the risk by first creating small strips of grout – lamellas – at metre intervals, before carrying out the main jet grouting.
A network of hydrostatic levelling cells, which measure movement to within a tenth of a millimetre, was installed to monitor the works and alert the crew to any issues.
A sustainable operation
One of the requirements of securing the contract for Keller was a commitment to reducing carbon emissions as much as practical – something the company is no stranger to. This meant using electrical rigs and other equipment, as well as ensuring suppliers delivered with electric trucks and workers got to and from site in electric vehicles.
“On the Stadtholder’s gate project, we were 100% emissions free, but for the basement phase, not enough electricity could be supplied to power the pumps and compressors,” says Marcel. “But to keep our commitment to environmental targets, we were able to use hydrotreated vegetable oil as a biodiesel for the pumps."
This wasn’t the only Keller innovation. The crew had set up on a temporary platform outside the complex, but space was limited, particularly when it came to storing the waste spoils for collection. Marcel and his colleagues came up with the idea of elevating the 30-tonne spoil container onto a stilt-like structure. The trucks could then drive under the container to collect the spoils.
Looking forward to the next phase
The basement phase of the project was successfully completed in October 2025 and Marcel says he’s proud of what the team achieved.
“Working on such a high-profile project definitely brings with it some unique challenges,” he says. “Every day there were politicians, tourists, the public and news crews around, so you always feel there’s a heightened level of scrutiny.
“But our team did a fantastic job, not only to complete the work to an excellent standard, but also to protect what is one of the most historic places in the country. We’re now looking forward to the next phases in 2026. These will involve us underpinning more entrance gates in the spring and the larger project of underpinning the Council of State building, starting in the second half of the year.”