The Extraordinary Technical Challenges of A Unique Historic Restoration

For 300 years Palais Het Loo was a royal palace. In 1984 it opened to the public as a historical museum. Changing needs, new aspirations and the need for repairs meant that the time had come for major improvements. In January 2019, the museum was closed to the public for a radical renovation of the existing listed buildings and expansion of the visitor facilities.

This project involves the creation of a 5,000m² underground extension beneath the central courtyard and existing 17^th century buildings and around 20,000m² of renovations to the original Palace.

WSP / Lievense is part of the technical Design Team alongside the MEP, Building Physics and Fire Safety Consultants and working with the award-winning Dutch Architect, KAAN Architecten.

We were also responsible for the construction management and BIM coordination on the project. 

The first and most significant delay to the project occurred during the initial design stages. An unusual geological formation was discovered. An ancient glacier had moved across the site pushing up an impermeable wall of iron oxide. This created two ground water tables each at different levels with a clear line of discontinuity across the proposed location of the basement. “There’s a height difference of around 50cm between the two water tables and to prevent significant inflows we had to keep the vertical water-tight layer intact when excavating the basement,” explains Eddy. “This unexpected complication had not been factored into the budget or the tight construction schedule – hence our decision to split the tender.”

A further challenge was to make the basement totally watertight. As much of the Netherlands is below sea level, Dutch Engineers are accustomed to factoring flooding into their basement designs. However, in this case, since the basement would become an exhibition space, there could be no risk of any water ingress. The innovative solution adopted to meet this requirement involves the use of concrete mixed with bacteria-filled capsules. These capsules break open if a crack forms releasing the bacteria into the crack. The bacteria react with water to create a limestone slurry that seals the crack making it water-tight. This is one of the first times that this product has been used in the Netherlands. The solution enables the Contractor to provide a robust guarantee for the integrity and water resistance of the basement walls.

Additionally, due to the high-water table the basement is continuously sitting in water, even during construction. Therefore, concrete cast underwater was used to form the floor of the basement pit. Tension anchors connected into this underwater concrete resist the uplift forces keeping the concrete floor in place. The concrete is reinforced with steel fibres, a relatively new technique in the Netherlands, that allows a thinner basement pit slab to be adopted and gives a reduced risk of deflection under the existing buildings. Casting concrete underwater is a common basement construction technique in the Netherlands but presents significant challenges with works carried out underwater with divers and consideration of the changing forced through the construction process.

The listed Palace buildings were jacked up to ensure no detrimental bending or distortion while the basement pit was being excavated below. Pressurised jacks were sat on temporary works and temporary foundations and remained in place during the pit excavation and basement construction. Once this work was complete the jacks were re-activated and the loads transferred from the temporary structures to the new basement. The whole exercise was undertaken with extreme precision. There was no more than 2.0mm deformation of the rigid, historic structures during the complete works!

The space excavated under the Palace Courtyard will eventually accommodate a new museum entrance area, a grand foyer and exhibition space. Above it, the courtyard will be heavily landscaped around a large glass roof light feature. Water will flow over the roof light creating a unique dappled light experience for the entrance area and foyer. The considerable weight of the new Courtyard is supported on the basement concrete retaining walls and heavy steel beams.

“Palais Het Loo is one of the Netherlands’ most popular museums and it is a privilege for WSP / Lievense to be working on such a high-profile project,” Eddy van Caulil concludes. “Since we became part of WSP, with all the additional global resources to boost our own multidisciplinary offering, we find that we can take on more complex and challenging projects like Paleis Het Loo much sooner than we had originally planned.”