When multi-storey apartment buildings are built from a basement excavation, the preferred method of shoring the basement walls is by ‘anchoring’. In this method, the walls of the excavation are ‘pulled’ back by cables that are anchored in neighbouring properties.
But at the 7-storey Toongabbie Residential Aged Care Facility development in Sydney, the surrounding property of the Aurelia Street site was not available for anchoring. So van der Meer Consulting - the engineering company providing services to the main contractor, Total Construction - opted to internally brace the excavation by ‘pushing’ the shoring walls from the centre with struts.
“Coates Hire’s engineers are experts in this work, and we worked with them to get a fast and innovative solution that would not slow construction.”
Senior Structural Engineer at van der Meer, Andrew Franklin, says the bracing option had to be well-designed to ensure the struts wouldn’t take-up too much space in the excavation and impede construction.
“The advantage of anchoring is that you have a clean and open site, because the anchors are in the surrounding ground,” says Franklin. “When you support the shoring structure of the basement internally with struts, they take up space inside the basement. A design was needed that left as much unimpeded area as possible.”
An additional problem was the ground-level concrete slab which was going to be poured directly onto the ‘capping beam’ of the shoring walls, which is where the bracing struts would usually connect.
Van der Meer contacted Coates Hire’s Engineering and Technical Services Team, and the teams of engineers agreed on an innovative design. They’d use eight MP150 hydraulic struts to shore the basement, two diagonally attached at each corner of the square excavation. To avoid having the struts below the ground floor slab - which would mean having to remove them when the slab was dry - they decided to place the struts above the ground-floor slab.
To do this they designed 16 ‘king posts’ that extended above the capping beam, which was designed to distribute the lateral loads into the piles and king posts. The hydraulic struts were attached to the king posts, leaving the ground-floor clear for the concrete pour.
“Coates Hire’s engineers are experts in this work, and we worked with them to get a fast and innovative solution that would not slow construction,” says Andrew Franklin. “We came up with a solution that didn’t require anchoring, gave us a large unimpeded worksite in the basement and allowed fast removal of the struts when they were no longer required, thanks to the king posts.”
Darren Browne, Engineer - Temporary Works, from Coates Hire’s Engineering and Technical Services Team, says the various criteria of the project included shoring it safely without anchors, creating additional space for working, and avoiding having the struts under the ground-floor slab.
“We were very happy with the Aurelia Street project,” says Browne. “It was suited to our hydraulic shoring system and the king post solution worked very well. In the end it’s about finding the best solutions for our clients.”
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