The Liberty of Southwark is a mixed-use office and residential development situated just behind Borough Market bound by historic warehouse buildings, a Network Rail Viaduct/Bridge and Crossbones Graveyard. The site itself is of high archaeological interest with its close proximity to the Victorian mass graveyard and previous archaeological digs within the site uncovering rare Roman remains of high archaeological importance. Beneath the site East and West bound Jubilee line LUL assets pass directly under. In 2022, during the archaeological enabling works, In 2022, the archaeological enabling works uncovered the largest Roman mosaic for over 50 years.
The Office building consists of a nine-storey building with a central reinforced concrete (RC) stability core linking and serving the two. RC columns support typically 250mm thick post tensioned (PT) slabs> The column layout was coordinated with the architects in order to minimise the transfer structures required at high levels, where the building steps back.
To the south of the office building is a residential building, four to eight storey high with RC blade column vertical structure supporting 200mm thick PT flat slabs. A three storey workspace building sits to the south of the residential building and it is built using Glulam and Cross Laminated Timber.
A single storey basement serving the office and residential building lies partially beneath the building footprint and sits 3m away from a network Rail viaduct and circa 20m above LUL’s Jubilee Line.
In the north-east corner of the site is an existing derelict building, 15 Southwark Street. The building is one of the former Calvert’s buildings and it is part of a conservation area. All the internal floors have collapsed, and the proposal is to refurbish the building and add a new internal structural to support new floors and a roof extension. The building will also be extended to the south in order to create an entrance stair and a lift shaft. RBG’s proposal is to minimise temporary works by installing the permanent structure as soon as possible in the works and use the permanent structure to retaining the existing façade walls.
RBG are the structural, civil geotechnical and geo-environmental engineers for the scheme. At Concept design, the team carried out a comprehensive comparison of the possible structural build-ups, including PT, Steelwork on metal deck or hybrid steel+CLT structures. The comparison was based on structural performances (such as depths, flexibility and column layout, building weight and foundation design, fire protection, maintenance, etc.), sustainability parameters (embodied carbon), multidisciplinary performances (overall MEP integration and response to architectural aspirations, etc.), costs and others. For the liberty, a PT slab over a 10.5x9m grid proved to be the most appropriate solution.
The presence of the Jubilee Line below the site heavily constraints the foundation opportunities. A raft foundation scheme is proposed with ‘short’ settlement piles terminating above LUL assets below, limiting ground movement. Where the building is found at ground level, ground improvement methods are proposed to improve the made ground bearing capacity and avoid mass excavation and backfilling. The foundation and basement construction sequence strategized limits impacts on archaeology and incorporates an archaeological dig conducted simultaneously with foundation construction
Sustainability
The project makes uses of high level of GGBS replacements and uses UK Cares sustainability Scheme reinforcement to keep the embodied carbon for the scheme to a minimum.
Furthermore, the Workspace building is a CLT structure with exposed Glulam beams and columns.
Finally, the external wall retention system proposed for 15 Southwark Street allows to save several tons of temporary works steelwork, which would have indirectly increased the embodied CO2 impact of the scheme.
Lessons Learnt
The archaeological findings on site as well as the large amount of ground obstruction and site history showed us the importance of de-risking the site before the works commence. The choice the Client and the design team made to carry out an enabling works package to de-risk the site before the main work started proved to be a very successful one.
The use of a pile assisted raft allowed to overcome the risk of large transfer structures at foundations. This required extensive Soil Structure Interaction analysis but allowed RBG to design a very efficient foundation scheme despite the ground constraints.
Project Metrics
Project Value:
£125,000,000
Year Completed:
2023
Building Metrics:
1,440 sqm Affordable Workspace
13,244 sqm Office
1,245 sqm Retail
2,657 sqm Residential
Sectors:
Commercial
Residential
Retail
Project Metrics
Client:
U+I
Architect:
Allies and Morrison
Robert Bird Group Services:
Civil Engineering
Geotechnical Engineering
Structural Engineering
Environmental performance
- Office embodied carbon target 600kgCO2/m2 (GIA)
- WELL Core Gold minimum
- BREEAM Excellent
- Residential embodied carbon target 500kgCO2/m2 (GIA)
- NABERS 5 stars