Concrete Basement of Dutch Royal Palace Cast Under Water

A MAJOR renovation of the royal Het Loo Palace in the Netherlands is currently underway.

Built in 1686, the palace served as a royal residence until 1962, when it passed into the ownership of the Dutch state. The palace was reopened as a museum in 1984.

Since 2015, the palace has been undergoing an extensive renovation, including the addition of a 4,500 square metre extension located under the building's front yard.

Above: The renovation includes additional exhibition spaces in the basement (image courtesy of KAAN Architecten).

This will create space for temporary exhibitions, expand visitor facilities and allow the curators to exhibit the palace's collection in new ways.

Because of the building's age and its status as a listed building, the architects have chosen to construct the extension underground.

Above: The extension is inserted underneath the building's front court (image courtesy of Paleis Het Loo).

However, the relatively high level of groundwater in the area - a common occurrence in the country - and the historic nature of the palace structure itself, prevented the excavation and dewatering of a large pit, which would have undermined the building's foundations.

Above: The site could not be dewatered, as that would lead to subsidence of the palace's foundations (image courtesy of Paleis Het Loo).

The solution to this problem was to use underwater concrete, which is cast underwater onto the excavated surface.

As the mixture is denser than water, it stays submerged and does not dilute if left undisturbed. Divers helped to guide the pour, which took 48 hours.

Above: Divers assisted with the 48-hour concrete pour (image courtesy of Paleis Het Loo).

Once the concrete had set, the area was dewatered to enable construction of the basement.

The museum is set to reopen its doors in 2021.

Above: A smaller adjacent space showing the state of the build once the floor has hardened and the water has been removed (image courtesy of Paleis Het Loo).