The new “Palais de Justice” is designed by the Dutch architectural practice OMA, partner of WSP in this ambitious project for the French Ministry of Justice. The courthouse is a colourful, geometric building designed to address different elements from the city of Lille’s past and present. It is located in the city centre close to a historic fortress built in 1667 by the French military engineer, Sébastien Le Prestre.
The building, which will house Lille’s high and district courts, has an irregular hexagonal form, with each façade finished in a different coloured glass. The large public courtrooms are located in the base of the building, below a triangular central tower where the small courtrooms are concentrated. The hexagon is suspended over an expanse of vegetation that connects with the surrounding natural landscape.
Structure Supports Courthouse Aesthetics and Procedures
Thanks to the project’s ambitious architecture, the first challenge was the structural design, which had to address some significant site constraints within a limited budget.
Architectural cross-section of the courthouse
The office floors in the superstructure are supported by reinforced concrete flat-slabs to provide maximum flexibility for future use, as well as to enable the architectural design and keep storey heights to a minimum.
A key client requirement was to avoid columns in the courtrooms. To address this, our team designed a range of different transfer structures above ground level.
The infrastructure for the utilities is located below groundwater level in the basement, where piling and diaphragm walls provide an efficient solution.
Another big challenge for WSP team was the proximity of a tunnel for the high-speed London to Paris railway. Tests revealed that this would produce excessive ground vibrations and noise in the courtrooms. To mitigate this we designed the entire courthouse structure using pre-stressed spring isolators to acoustically isolate it from the ground.
In addition, the building is located in an area of low seismic activity. While the structure is designed to accommodate mild seismic events, the acoustic isolators provide additional protection against ground movements since they substantially limit the load transmission from the ground to the isolated structure above.
Some continuous floor lengths in the primary structure above the isolation system are greater than 90m. Our integrated design solutions remove the code requirement for movement joints on these long floor lengths, made possible through the careful specification of the reinforced concrete and giving clear instructions to the construction team on phasing during construction of the different floor elements.
Enhancing Design, Performance, Safety and Security
The design team is facing several MEP technical challenges relating in particular to the complex geometry of the architecture and to the requirement for the accessible green roof. We developed a BIM model, shared weekly with all stakeholders, to facilitate day-to-day coordination and avoid impact of building services infrastructure on the green roof.
The sustainability ambitions were also challenging for a geometrical building with an extensive glazed façade and internal atrium. To ensure a comfortable indoor temperature while minimising energy consumption, we carried out thermal modelling for all the physical components of the building to achieve the best performance of each element, such as glazed facades, insulation and chillers.
The security strategy was central to the design of the courthouse, given its sensitivity in terms of protecting the public, justice employees, detainees and police officers. We worked with stakeholders from the ministry to develop optimum accessibility strategies for each user category, responding to the client’s requirement of creating separate circulation patterns for detainees, the public and justice employees. CCTV and other security systems were implemented to provide a high level of security for both the internal and outdoor spaces around the building.
The fire security strategy was also critical and we held regular meetings with stakeholders and the fire brigade to identify all the fire risks and fully understand the fire-fighters’ requirements in terms of intervention and accessibility for all rescue services.