Image: Copyright Mike van Bummelen

A unique engineering solution enabled what is the deepest underground car park in the Netherlands to be built in a city centre without disturbing the foundations of surrounding historic buildings. Furthermore, the design delivered faster construction at lower cost than other options.

Leiden, the birthplace of Dutch painter Rembrandt, is rich in cultural heritage and fine buildings, including a working windmill dating back to 1743. Requiring more parking for residents and visitors, the municipality sought tenders for a 525-space car park concealed underground in the city centre. One of the key concerns was that the stability of Leiden’s historic buildings should not be affected.

Water extraction creates a challenge

Royal HaskoningDHV provided structural design services for a seven-storey circular car park sinking 23m underground – the deepest car park in the Netherlands. The circular design increased the stability of the structure, avoiding the need for extra reinforcement and reducing impact on nearby building foundations during construction.

However, a key construction challenge remained. Once the foundations had been built, water inevitably rose into the hole. The concrete base was formed but, because concrete shrinks when it hardens, it was not possible at this stage to create a water-tight seal with the walls. The challenge was how to remove the water in the hole while avoiding the risk of further seepage which could present a risk to the foundations of nearby buildings.

Unique solution involves freezing soil

Various alternatives were explored drawing on the specialist knowledge and expertise of our geotechnical department. A unique solution was chosen. This involved freezing the surrounding soil before extracting the water and sealing the floor and walls.

With this successfully managed, the rest of the building was constructed using pre-cast concrete sections. The result was a high-quality, modern car park with a central atrium from which drivers can see all floors.

High-quality end result constructed more quickly and at lower cost

“The unique approach we applied was necessary due to the location close to such significant buildings,” said Frans de Zwart, consulting engineer at Royal HaskoningDHV. “What was also special about our solution was that it offered quicker construction and at lower cost than alternatives to create a high-quality end result.”