Everton Stadium is raised above the ground on a series of podium slabs to limit the effects of settlement over the coming years.
The 52,888-seater stadium is well over a year into a build that will provide the Club with a state-of-the-art future home at Bramley-Moore Dock.
And the development’s waterfront location, along with the huge maritime engineering feat of filling in the semi-derelict dock, has, as a result of some ingenious engineering, led to a unique solution to counter any minor settlement of the sand-based foundations.
“The dock location led us to design the stadium as a fully suspended structure of concrete piles and slabs suspended between the pile caps,” explained Gerald Knights, engineering lead for construction partner Laing O’Rourke.
“A decision was made early in the project to retain the dock’s silts, which isn’t particularly normal for this type of project.
“We did it because it is really great for the environment, although it does give rise to an engineering challenge.
“As the silts are compressible, settlement is inevitable. A lot of this settlement happens as soon as you put the sand in, and once we had put 1m of sand in the bottom of the dock, most of the settlement in the silt happened.
“Once we got up to dock ground level, the dock was settling somewhere around 5mm per week. We are now down to less than that a month.”
The stadium is therefore supported by 2,766 concrete piles, each formed to a depth of around 18 metres through the dock infill and into the sandstone below.
The piles are then capped by concrete floor slabs, to provide extra stability, which essentially creates a podium on which the superstructure is constructed, leaving a void beneath, in which the stadium’s utilities will run.
There are elements of the development that are not supported by piles, including the pitch which lays directly on top of the infill.
However, any minuscule settlement on site is carefully monitored by Laing O’Rourke, who have been delighted to see the numbers fall well within planned tolerances.
“Essentially, that settlement will continue for decades," added Knight, speaking to New Civil Engineer.
“It will slow down to fractions of millimetres a year, but there are a few phases in the project’s lifetime when certain interventions will be needed to address that. For example, the club may have to relay the pitch in the off-season”.
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