Nova is the £400m first phase of a mixed-use development by Land Securities in the heart of Victoria between Buckingham Palace Road, Bressenden Place and Victoria Street. It comprises two commercial buildings of 13 and 17 storeys (total 46,000m2 office area), a 13-storey high-end residential building (170 apartments) and ground level retail. There is a four-level basement with two primary levels (B2 intermediate and B4 raft) and two mezzanines, B1 and B3.
Key technical challenges
Key technical challenges included mitigation of risk with respect to third party assets and infrastructure, whilst minimising overall construction time to maximise commercial viability, also future-proofing for new infrastructure and later development. The design process began with a detailed review of the overall site, the phasing possibilities and interfaces, the technical parameters regarding third party assets and adjacent infrastructure, building massing, impact of existing piled foundations and suitable foundation type. This review highlighted the sensitivity to ground movement of buried infrastructure, particularly LUL and VSU assets and vertical displacement of the sewers. The design for the permanent solution integrated the requirements for the construction phases, taking into account the load-history over the entire demolition, excavation and construction process.
RBG worked closely with the relevant authorities to understand the effect of ground movement and developed an early proposal for partial top-down basement excavation combined with jump-start technique for the six slip-formed concrete cores, columns and floors.
The construction materials and methods are fundamental inputs to the structural design for any project. However, when a top-down method is adopted this heavily influences the design of various elements particularly the basement columns and slabs. They are required to perform functions during the early stages of construction that are unique to the methodology.
Adding an early start to the core construction adds another layer of complexity to the structural design. The top down / jump start approach had several advantages, including:
- Programme efficiency and flexibility: building up whilst digging down.
- Significant overall savings on construction time (over conventional top down approach)
- Basement excavation direction prioritised to enable the concrete framed residential building to be completed early to suit the extensive fit-out period and early marketing.
- Early establishment of construction access route, reducing traffic disruption on adjacent ‘red route’ roads.
- Minimised retaining wall movements, important for adjacent assets and LUL/ VSU works.
- Controlled application of load (confinement pressure) on the WDS Sewer below the site.
- Elimination of temporary works, through incorporation into permanent works design.
Sustainability
The project adopted the normal approach to use recycled steel for reinforcement as well as cement replacement in the concrete mix designs however the real sustainability gains were found in the construction methodology that reduced the requirement for temporary works during construction and accelerated the construction program.
The top-down construction approach utilized the permanent basement structure to support the excavation without the need for internal temporary strutting.
The methodology also adopted a jump start approach that saved time in the construction program. The methodology also adopted strategic sequencing to limit the impact of ground heave movement on the existing inground infrastructure. This reduced the requirement for extensive temporary protection measures to ensure the assets remained serviceable throughout construction.
Project Metrics
Project Value:
£400 million
Year Completed:
2017
Building Metrics:
Total Area: 1.3m sqft
Site footprint: 13,000m2
Levels: Three towers (13, 13 and 17 storeys). Four level basement.
Sectors:
Residential
Commercial & Retail
RBG Client:
Land Securities
Project Metrics
Primary Contractor:
Mace
Architect:
PLP Architecture
Flanagan
Lawrence
Benson+Forsyth
Robert Bird Group Services:
Civil Engineering
Construction Engineering
Structural Engineering