Salisbury Square Justice Quarter, London
Salisbury Square, Justice Quarter, London
Client: City of London Corporation
Main contractor: Mace
Demolition contractor: Keltbray
Structural engineer: Buro Happold
Value: £596m
Creating the City of London's new Justice Quarter to house new law courts, police offices and commercial offices. This complex project involved demolishing six existing buildings with different construction types and basement levels, then excavating 20 metres down in the heart of London’s Fleet Street.
We had to preserve and stabilise the Grade II listed Salisbury Court building where the first edition of The Sunday Times was printed, and manage the entire operation above Thames Water sewers and multiple below ground services while surrounding businesses remained operational.
We had to preserve and stabilise the Grade II listed Salisbury Court building where the first edition of The Sunday Times was printed, and manage the entire operation above Thames Water sewers and multiple below ground services while surrounding businesses remained operational.
6
Existing buildings due for demolition with different forms of construction and basement configurations
20m
Deep basement excavation in the heart of a constrained city centre site in London's historic Fleet Street.
10m
Up to 10m below ground capping beam excavation to span large column loads.
Our role
Our roleWentworth provided temporary works and construction engineering services from pre-demolition stage through to construction of the new basement and core construction.
Due to the challenging nature of the site, the temporary works design was split activities into two distinct phases:
Due to the challenging nature of the site, the temporary works design was split activities into two distinct phases:
- stage one propping
- stage two propping, and site investigations and analysis of damage criteria adjacent structures to determine temporary works methods.
CAPABILITIES
CAPABILITIES- Buildings
- Demolition
- Substructure
- Structural Engineering
- Geotechnics
- Construction Method Engineering
- Temporary Works
- Inspection and Testing
Demolition strategy, Grade II listed retention
Demolition strategy, Grade II listed retentionSix buildings with varying construction types and basement levels required different demolition approaches. The retained pub and party wall on the south of the site needed stabilisation but installing propping in the site would have disrupted demolition, piling and excavation for months.
Our solution was to justify the stability of the adjacent building and tie the pub to it, securing all necessary approvals to do so. This kept the site fully workable for the phases that followed.
For the listed Salisbury Court building, we developed a phased construction sequence maintaining the façade and gable wall's stability while we demolished, structurally altered, undermined, and excavated directly adjacent to it.
Our solution was to justify the stability of the adjacent building and tie the pub to it, securing all necessary approvals to do so. This kept the site fully workable for the phases that followed.
For the listed Salisbury Court building, we developed a phased construction sequence maintaining the façade and gable wall's stability while we demolished, structurally altered, undermined, and excavated directly adjacent to it.
Piling optimisation for 20m deep basement
Piling optimisation for 20m deep basementTransitioning six buildings with different basement configurations to a continuous piling sequence required detailed investigation. Our in-house site investigations team assessed the existing retaining walls, then mapped obstructions and services to determine the optimum perimeter pile wall alignment.
We took the existing ground and basement levels into consideration, and proposed capping beam levels to minimise the length of pile bored while providing continuity of work and minimising the number of different piling levels.
The process of optimising the perimeter pile arrangement through site investigation de-risked the piling operation, providing cost and programme certainty for the demolition contractor Keltbray.
We took the existing ground and basement levels into consideration, and proposed capping beam levels to minimise the length of pile bored while providing continuity of work and minimising the number of different piling levels.
The process of optimising the perimeter pile arrangement through site investigation de-risked the piling operation, providing cost and programme certainty for the demolition contractor Keltbray.
Capping beam construction up to 10m
Capping beam construction up to 10mCapping beam construction required excavation up to 10m below ground level. This depth was necessary because the capping beam had to span large column loads and sit below the pile caps while maintaining viable floor levels for the final building.
Varying site conditions meant no single construction approach would work across the entire basement. We deployed multiple techniques including cantilever king posts, propped kingposts, skin walls, cofferdams, and propping to existing basement walls, with each method selected based on local existing conditions.
Varying site conditions meant no single construction approach would work across the entire basement. We deployed multiple techniques including cantilever king posts, propped kingposts, skin walls, cofferdams, and propping to existing basement walls, with each method selected based on local existing conditions.
Basement retaining wall design and propping
Basement retaining wall design and proppingTo design the pile walls and propping system, Wentworth carried out a detailed assessment of the ground conditions. By also conducting additional ground investigations with detailed finite element analysis, we were able to design out the requirement for a third level of props for the 20m deep basement. Removing this propping saved both cost and time by streamlining the construction process and enabling more efficient excavation.
The basement propping solution was a hybrid of sustainable proprietary hired props together with bespoke props where the loading dictated, however these props were designed in modular lengths for re-use. The retaining wall and propping system performed in line with the predicted analysis, enabling a predictable and efficient basement construction.
The basement propping solution was a hybrid of sustainable proprietary hired props together with bespoke props where the loading dictated, however these props were designed in modular lengths for re-use. The retaining wall and propping system performed in line with the predicted analysis, enabling a predictable and efficient basement construction.
OUTCOMES
OUTCOMESThis project shows what can be achieved when construction engineering is brought on at the early stages of a project and how we can help deliver predictable, efficient construction without the typical cost overruns and delays usually associated with complex city centre basements with heritage constraints.
Key results:
Key results:
- Programme certainty: pile optimisation and propping reduction saved months
- Design performance: retaining wall behaviour matched finite element analysis predictions
- Heritage protected: listed building remained stable through all phases
- Cost savings: eliminated third propping level and optimised pile arrangements
- Contractor confidence: Keltbray could execute demolition with certainty