The challenge
Burnside, the sheet piling and foundation contractors, was appointed to provide the retainment solution.
Speaking about the project, James Miller, Head of Operations for Burnside Piling said: “For the temporary works part of the retainment solution, essential for enabling the safe excavation of the ground to the required depth of 5.2 metres, we turned to Mabey Hire for their support. We’ve always had a good relationship with the Mabey Hire team and often choose to work with them, especially on the more complex schemes. For temporary propping, as on this project, they are our go to supplier.”
While the initial concept was to have sheet piles installed cantilevered, it transpired that cantilever piles wouldn’t have worked in a permanent state. Working closely with Burnside and engineering consultants Richter, we proposed an alternate temporary propping system that would allow the contractor to get to the required depth.
Our solution
The scheme involved the installation of 10m sheet piles around the perimeter of the excavation, supported by 15 raking props and two knee brace props. The temporary works utilised Larsen piles and modular frame extensions as a thrust restraint for the raking props, providing an environmental and practical alternative to traditional concrete thrust blocks. As part of the permanent works, a retaining wall was designed and constructed to cast against the base of the sheet piles. This would then allow the removal of the temporary works, with the sheet pile wall acting in cantilever in its permanent state.
Jamie McLachlan, Regional Sales Manager at Mabey Hire, explained: “It was essential that we were able to adapt our propping design to suit the project’s critical parameters - specifically, working around the permanent works elements. The angle of the props had to be sufficient so that they wouldn’t clash with the permanent structures during any phase.
“It was also a requirement that the props were supported at the lower level. We coordinated with Richter very early on in the project in this regard, with the consultant responsible for the design of the thrust restraint and sheet piles. After much discussion, it was decided that this was the most sustainable and economic solution, negating the need for soil anchors.
“The whole system required careful planning and communication, with both permanent and temporary elements featuring within the retainment scheme and careful consideration required to where the two intersect. We were in constant dialogue with both Burnside and Richter throughout, ensuring a smooth project delivery.”
The temporary support scheme featured our Super Bracing Strut mechanical props and the versatile hydraulic Super Shaftbrace. From initial contact, our dedicated teams turned around the design and supply of the equipment in under five weeks, ready for Burnside to install on site.
The temporary props and sheet piles remained in place for 10 weeks while a permanent concrete retaining wall was constructed.
Burnside’s James Miller concluded: “The project progressed really smoothly, with Mabey Hire pulling out all the stops in terms of getting their kit to site in time. In fact, we completed the construction of the permanent retaining wall ahead of schedule, meaning the temporary elements were able to be removed earlier than planned. Once again, Mabey Hire’s in-house team promptly returned to site and expertly disassembled their equipment.”
