Project description

The City's Service Ouvrages d'art (Civil Engineering Department) is currently extending and renovating the Knuedler car park.

Below is an overview of the car-park renovation project:

Description of the works

Umbrella arch

With an access zone of only 500 m2, the City of Luxembourg is extending the entire car park using the Umbrella Arch Method (UAM). The first phase of these works involves creating an umbrella arch, for which around 100 metal tubes will be inserted into the ground horizontally over the entire area of the planned extension. At a depth of 3.5 m under Place Guillaume II, this umbrella arch will serve as the car park's ceiling slab.


To support the weight of the public square above, around 50 vertical piles will be installed at a distance of around 5.5 m from each other, going down to a depth of around 20 m.


The umbrella arch is supported by beams resting on the piles.


As part of the excavation works, 8,800 m3 of soil will be removed to make room for the new extension.


Once the excavations are complete, the foundation and walls will be installed. The foundation will also serve as the floor of the lowest parking level (-5).


To finish off the concreting, the slabs and walls for the remaining floors (levels -4 to -1) will be installed, working from the bottom to the top, as with the construction of a normal building.

Works schedule

Commencement of work: January 2016

Scheduled reopening: 2023

Traffic information

What is the current traffic situation?

For cars and pedestrians:

Most of the work will be carried out inside the large fenced-off areas. Traffic on Rue du Fossé will not be affected. During the work, most parking spaces in the Knuedler car park will remain accessible. In the event of any changes to vehicle access, appropriate signage will be put in place.

For businesses and deliveries:

The City of Luxembourg will ensure that deliveries to local merchants can continue uninterrupted throughout the duration of the works. Access to Place Guillaume II by way of Rue du Fossé will be remain open.

The City of Luxembourg thanks local residents, businesses and road users for their understanding and apologises in advance for any inconvenience caused.

Progress to date

What work has already been completed?

Archaeological digs undertaken by the National Centre for Archaeological Research (Centre National de Recherche Archéologique – CNRA). Boring of post holes and erection of metal posts. Demolition and reconstruction of the staircase on the north-western side (now open). Jacking and injections to build the umbrella arch. Erect girders to link the umbrella arch and vertical columns. Excavation work for level -3.

What remains to be done?

For the new extension, the excavation work for all 5 sub-levels will be finished by the end of March 2021. The underpinning works for the ramps of the existing car park and stairwells remain to be finished. The excavation work for the sprinkler tank is being carried out at the same time. After this, the five sub-levels of the new extension to the car park will be built. 

Contacts for this work site




Service Ouvrages d'art

Claude Peschon


Construction mediators