Gabion baskets are being used in a wall to form a perimeter wall around BBC film sets in Cardiff. GE reports
There is not much similarity between a hospital ward and a high security prison.
But for a new project in Cardiff they do have something in common: a 6m high perimeter wall.
But this is no ordinary wall. It is being built as a carefully landscaped feature, with a sandstone facing and some vegetation.
Instead of concrete or brick it will be made from layered stone within gabion baskets.
“It is an unusual application for a technique more usually used for ground or slope support,” says Lee Church from Maccaferri Construction, which is building the wall for main contractor Vinci Construction.
It is part of a new £10M BBC “village” of studios in the city.
The hospital is, in fact, a new studio and outdoor set location for high definition filming on the long-running TV series Casualty.
Standing alongside are even larger studios for a different medic, Dr Who.
Both are being created on a plot of land in the now disused part of the former docklands, part of a major regeneration programme triggered by the completion of the Cardiff Barrage 10 years ago.
Nearby stands the Welsh Assembly and the new opera house, as well as offices, apartment blocks and retail outlets, that are gradually filling the bay area.
The wall is needed not to keep the actors in, nor fans and spectators out, though it might do that.
Rather it has an acoustic and visual function, blocking off noise and views of roads from the sets and allowing outdoor scenes to be shot.
Directly behind the wall, for example, will be a 120m long “ambulance run” for filming high-speed arrivals.
“The BBC site has several major studio ‘boxes’ and an office building,” explains Vinci project manager Kieran Mulrooney.
“But also outside are sets for streets and the like.
These are protected by steel and timber acoustic walls on a blind side near a dock, but on the other side this would be unsightly.”
Vinci’s overall contract is for the £30M redevelopment of a 900m long and 400m wide area of regenerated dockside land.
This will have various other plots and a new spine road through the centre.
To fit in with the overall context, the landscape architect LDA chose the unusual gabion wall solution.
It is filled with two different colours of a local sandstone to create an appearance which is “something like a natural cliff face”, says Mulrooney.
“The difficult part comes as the wall gets higher when we must fill it from scissor lifts,”
The filling, Gwrhwd sandstone, is from a quarry near Swansea, which has a large amount of paving stone offcuts.
The irregular slabs create a “strata” effect on the wall facing.
The wall dimensions are quite particular. It is 675mm wide and 6.5m high.
It is formed in 2.7m long sections each made up of three gabions.
These sections are held in place at each end by steel H-section kingposts bolted to a reinforced concrete foundation.
The spacing, chosen by structural designer Bay Associates, is the widest possible without having to pile the concrete footing for the wall, says Mulrooney.
To make the wall sections, Maccaferri fits two 1.5m long galvanised baskets, with a dividing wall in the middle, and a central 1m long basket.
These baskets are made from a 4mm welded, 75mm by 75mm wire mesh with a double twist, “which is the constraint to set the wall thickness”, says Church.
These baskets are unfolded from the factory “flat pack” and cut to fit around the steel posts before being fixed together with CL50 clips at the top and bottom and to each side.
They are then hand-filled with slabs both on the outer side and the inside, with a loose stone added finally to fill the remaining space.
“The difficult part comes as the wall gets higher when we must fill it from scissor lifts,” says Church. “That means taking up the stone in small skips on the platform and leaning over.”
Not all of the 475mm deep steel posts show at regular intervals on the new face, as some are “randomly” set back to the rear to give an irregular sequence, visually breaking up the outer wall facing.
Where they do show, they will be faced with Siberian larch timber, which is being used for a cosmetic finishing facade on the new office block and the new wall is needed only where it finishes, extending 123m to the end of the site and then around a corner.
The wall will be finished with coastal plant species planted at the top, and ivy planted at the base so the wall will have a matured vegetated appearance, hopefully as unlike a prison as possible.