Building beneath London – temporary works innovation

Salisbury Square, London

Project Overview

Location	Salisbury Square, London
Sector	Building
Products	250Te End Unit Supershaft Plus Steel Walers Screwed Ram Jacks Propping & Jacking

When working on a basement excavation project in London, the ability to adapt to changing site requirements is essential. When the project is of the size of Salisbury Square, this becomes even more paramount, with Keltbray relying on our expertise, innovation and comprehensive temporary works offering.

The challenge

Complex Site Footprint

Covering over 5,000m² in the heart of the City of London, the project’s size and scale presented major logistical and engineering challenges. The temporary works had to accommodate multiple excavation zones and interface with several ongoing construction activities. Mabey Hire delivered a coordinated temporary works package that provided flexibility and strength across the entire footprint while maintaining access and programme efficiency.

High load demands

Excavating a three-storey basement created significant lateral pressures and load demands on the retaining walls. The temporary works system needed to safely resist these forces while enabling construction to proceed at multiple levels. Mabey Hire provided a robust propping and bracing solution, designed to handle complex load paths and ensure excavation stability throughout all phases.

City Constraints

Located within London’s historic Square Mile, the project was surrounded by sensitive buildings and existing underground infrastructure. Strict vibration, movement, and noise limits had to be met to protect neighbouring assets and ensure regulatory compliance. Mabey Hire’s engineering expertise allowed for a tailored solution that balanced structural performance with minimal impact on the surrounding environment.

Our solution

Our temporary works solution combined a range of our Super Bracing Struts (SBS), from 400mm to 1000mm, alongside our Supershaft Plus bracing system and Steel Waler Frames to manage the significant loads of the project. Recognising the need for even greater capacity, we designed and developed a bespoke 1200mm diameter prop—the largest of its kind—specifically for this scheme.

Early collaboration with the project team was vital, allowing us to deliver the temporary works design 12 weeks in advance while maintaining flexibility to adapt the prop design as new site data emerged. We also re-engineered our hydraulic screwed ram jacks, traditionally used above ground, to integrate with the new props and achieve the required high load capacity.

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In addition to designing and supplying the temporary works equipment, we worked closely with Keltbray’s site teams to ensure seamless installation and performance. Our in-house hydraulic jacking team handled the pre-loading of the props and jacks, ensuring precise installation and safety.

This collaborative approach enabled efficient coordination between Mabey Hire, Keltbray, and Wentworth House Partnership, overcoming the logistical and technical challenges of a busy city-centre site. The project stands as a testament to our shared engineering expertise, adaptability, and proactive approach in delivering complex groundworks support solutions.

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“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.”

Sinan Atasoy

Project Director/ Keltbray