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Retail–residential project marks a new phase in the redevelopment of Leuven’s Hertogensite

A building along Brusselsestraat that combines retail and residential functions marks a new phase in the implementation of the Hertogensite master plan in Leuven. It is being constructed on the site of the former Sint-Pieters Hospital and directly adjoins the former Sint-Pietersgasthuis, which has since been converted into a hotel. Both above and below ground, the new building presented a wide range of challenges.

The building is 80 metres long and 25 metres wide and is divided into two parts by an expansion joint. The ground floor and level –1 are dedicated to retail use. Above this are three residential floors, with a fourth floor accommodating a penthouse over a limited portion of the footprint. The retail space on level –1 will be occupied by Spar. On the ground floor, shell units are provided that can be further fitted out and subdivided by future owners and/or tenants.

 

 

Underground challenges

A spacious underground car park is provided at level –2 for residents and shoppers. In the future, it will also be able to serve the adjacent performing arts building that is scheduled to be realised in the coming years. This building will not be developed by Resiterra but will be owned by the City of Leuven. From both a structural and technical perspective, it was essential to design the substructure of the mixed-use building in such a way that a future connection to the car park of the performing arts building can be made and properly coordinated.

 

 

A first challenge was that, for the excavation support along the public domain, no permanent ground anchors were allowed. All elements had to be fully removable. To address this and avoid anchors extending beneath Brusselsestraat, a bracing frame was used. This truss structure, composed of heavy steel tubes, was installed inside the excavation pit, eliminating the need for anchors outside the pit to retain the soil-mix wall. This demanding work was carefully planned and executed in close coordination with the contractor.

For the construction of the performing arts building, the basement will need to be excavated one and a half metres deeper than that of the mixed-use building due to technical requirements. As this will take place at a later stage, the superstructure of the mixed-use building would impose additional loads on its own soil-mix wall. This could be addressed in two ways: either the city could install a new soil-mix wall with a finishing wall for the performing arts building, or the soil-mix wall bordering the second project could be designed from the outset to be sufficiently robust to accommodate the loads of both projects. By opting for the latter solution and sharing the costs, both Resiterra and the City benefit—one reinforced soil-mix wall is more economical than two separate ones—and the City also literally gains usable space in its own car park.

 

 

Old and less old remains

Before excavation could begin, further underground challenges were encountered. The former hospital comprised some 15 above-ground floors and was founded on massive foundation piles with a diameter of 1.6 metres. Along the alignment of the retaining wall, these piles first had to be removed. At ground level, however, they could be left in place, provided the locations of the new foundation piles were carefully coordinated. This added considerable complexity to the foundation design.

While underground remains of the old city walls were anticipated, an old mass grave dating back to the plague era was not. Layer by layer, archaeologists uncovered 140 skeletons. This resulted in a delay of two additional months. To recover lost time and deliver the building by summer, the decision was made to construct the superstructure in sections rather than floor by floor. As a result, the left-hand section will reach its full height sooner than the right-hand section. The expansion joint between the two sections is also more economical than constructing the building without a joint but with additional reinforcement to accommodate differential settlement between colder and warmer periods.

 

 

Complex beam layout

The vertical load transfer of the superstructure is a complex puzzle. The load-bearing walls of the apartments do not align optimally with the column grid of the retail spaces (8 × 8 metres), which in turn transfers loads onto an identical grid in the car park. The stair cores of the superstructure only start at level +1, and the retail floors had to be designed for very heavy loads (up to 1,000 kg/m²). The apartments overlooking the Dijle also feature projecting balconies, whose loads must be accommodated at ground floor level. In addition, the shell design of the ground-floor retail units required flexibility for ventilation and lighting layouts according to the future users’ needs.

All of these factors result in a complex beam grid above the ground-floor transfer slab, which distributes loads to the retail columns and subsequently to the foundations. With spans of up to 8 metres, some beams reach heights of up to 1.8 metres. To maximise open space within the retail areas, column dimensions were kept to a minimum by using heavy reinforcement and high-strength concrete. The retail floors were designed as flat slabs, avoiding overly deep beams in the basement (thereby creating more space for technical installations) and eliminating the need for further—and costly—deepening of the basement. This approach also allowed excavation volumes to be kept to a minimum.

 

Construction Partners: