Groundforce Shorco has supplied a modular hydraulic support system to shore up the basement excavation on a prestigious city centre development in Manchester.
Concrete frame and groundworks specialist MPB Structures called on Groundforce to provide support for the 85m long, 40m wide basement excavation for the £96m second phase of the Circle Square development which main contractor Sisk is building for developer Bruntwood.
The original plan had been to support the excavation with structural steel props in the traditional manner.
The change to a 2 stage propping solution to advance the construction of the cores meant the flying shores were in for a shorter duration of time.
The basement perimeter retaining wall comprising concrete secant piles and capping beam had already been installed.
Groundforce were required to install one level of props, braced against the capping beam to support the top of the piles as MPB excavated.
Groundforce major projects manager Andy Simms said: “This isn’t normally how we do it.
“Usually the props would be assembled on the ground and secured against the capping beam before the contractor had excavated more than a couple of feet down.
“MPB had already excavated about 4m in the middle of the excavation to allow the piling of the bearing piles to commence and had battered the sides for support.”
The props (which were up to 38m in length) were assembled on the piling mat and then them lifted into position by a mobile crane.
Groundforce provided four days of site assistance from their dedicated project co-ordination team to support MPB during the installation.
Due to the change in the scheme, no provision had been made in the capping beam for knee braces to connect the capping beam and so, Groundforce’s technical team came up with a bespoke solution.
Simms said: “We designed bespoke shear plates with post-drilled resin anchors which took the load into the capping beam.”
Despite the complex geometry of the capping beam, which incorporated multiple steps, penetrations and cast-in items, Groundforce quickly provided the custom-designed connections for each of the 16 prop ends.
In total, Groundforce supplied eight props of both 150 tonne and 250-tonne capacity.
Simms said: “The need to hire a 130-tonne crane was costly, however this was offset by the time it saved installing the props. We were able to offer the quickest and most efficient solution.”
The props will remain in place until the basement slab has been cast and the permanent works completed.
from Construction Enquirer http://www.constructionenquirer.com/2018/11/06/groundforce-gets-to-work-on-massive-manchester-basement/
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