The challenge
Once completed, London’s Salisbury Square development, funded and delivered by the City of London Corporation, will become a flagship facility for His Majesty’s Courts and Tribunal Services (HMCTS). It will include 18 courtrooms and the new headquarters for the City of London police. Located in the heart of the city’s historic Square Mile, the project aims to strengthen the City’s justice system and promote London’s standing as a premier location for business and innovation.
Keltbray, the specialist engineering firm, was appointed by main contractor Mace to deliver the project’s substructure works. When it came to excavating the three-storey basement substructure, considerable temporary works were required to facilitate its safe and efficient delivery. Here, Keltbray turned to us for support, having worked together on numerous basement excavation projects in the past.
Speaking about the project, Arran Phillippou, Major Projects Sales Manager at Mabey Hire, said: “Salisbury Square is a really unique project and has presented some considerable challenges from a temporary works perspective. First, is the sheer size of the development, with the site footprint covering over 5000sqm. Second, is the depth of the excavation and the significant loads encountered as a result. Finally, given the city-centre location, there was the added challenge of surrounding infrastructure and structures, with strict criteria and requirements to adhere to."
Our solution
Arran continues: “Our proposed scheme featured a variety of our Super Bracing Struts (SBS), ranging from 400mm to 1000mm, in addition to our Supershaft Plus bracing system and Steel Waler Frames. Due to the immense loads presented by the project, a larger capacity prop was also required. As a result, we decided to invest in the design and development of a new 1200mm diameter prop specifically for this project.
“Here, having the expertise and ability to effectively react and adapt to changing site conditions and requirements was critical. Due to the need to design and manufacture the new bespoke props, early collaboration was essential, with the temporary works design delivered 12 weeks in advance. However, as construction work commenced and new information came through from site, we had to be able to adapt both the prop design and our proposed temporary works scheme to reflect this.
“In addition to the high-capacity prop, we also looked into utilising and remodelling our hydraulic screwed ram jacks - typically used for above-ground applications - for installation on the props, in order to deliver the high capacity required on this project.”
Originally contracted to deliver a cofferdam made up of sheets, piles and props, we are now supplying the top storey basement props, as well as groundworks support equipment for the third-storey excavation level.
As the project progressed, the temporary works requirements also further evolved, making it important that the chosen supplier could keep up with site demands and have the equipment range and expertise to match. For example, we also supplied above ground propping to support and retain a listed building, which was located within the site footprint. While, given the project’s location, MOLA (the archaeology and heritage practice) was also brought in to carry out investigative works, which required additional temporary works to facilitate.
As well as designing and supplying the temporary works equipment, we worked in conjunction with Keltbray’s site teams on the installation. Our in-house hydraulic jacking team took responsibility for pre-loading the props and jacks, providing added peace of mind that they were installed correctly.
Speaking about the project, Sinan Atasoy, Project Director at Keltbray said: “Salisbury Square is a great example of collaboration between Mabey Hire and Keltbray, a complex ground engineering project with technical constraints and logistical challenges being in the city centre. The proactive approach from Mabey Hire has made the process easy, with great coordination with our in-house temporary works designer Wentworth House Partnership. Both Keltbray and Mabey Hire have carried out basement propping projects in the past, collectively and separately. Salisbury Square is a great example of both business’ engineering capabilities.”
Arran concluded: “It’s been an honor to work with Keltbray and Mace on such a landmark project, with the site’s unique challenges directly feeding into and influencing our ongoing product research and development. We’ve worked with Keltbray on numerous basement excavation projects in city centers and have a strong relationship, having clearly demonstrated our expertise and robust offering.”
