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MELTING MOMENT

PILING

Spanish cash is set to regenerate a disused manufacturing site in Cardiff, creating new jobs for the area. But the piling work has met steely resistance.

Allied Steel and Wire, once a major source of steel reinforcement for the construction industry, went into administration over two years ago but its old works in Tremorfa, Cardiff is being revived.

Barcelona-based Celsa Group took over the plant from the receiver, demolished part of the former works and is building a new melting shop.

The facility will house a 140t electric arc and ladle furnace feeding a six-strand continuous billet casting machine, producing 1.2Mt/year of different sections from steel scrap.

Slag from the furnaces will be processed and recycled for construction back'll.

German company SMS-Demag is building the £100M project and Cementation Foundations Skanska and Aarsleff Piling installed the extensive piling.

The £2.1M contract required a combination of 681 CFA and 1,022 precast concrete driven piles.

Cementation no longer has the facility to manufacture precast concrete piles so it negotiated a £750,000 subcontract with Aarsleff Piling to supply and drive them.

Several types of CFA and driven piles were required to accommodate a variety of compressive loadings on the project. The CFA piles, with diameters of 600mm, 750mm and 1,050mm, were designed for compressive working loads from 1,500kN to 4,700kN.

The three types of Aarsleff's 300mm square section precast piles used have compressive loads from 210kN to 1000kN.

The project's 1,700 piles have to accommodate 10% of their allotted compressive loading in tension as a minimum requirement with some having an increased tension loading.

The precast concrete piles also have to absorb lateral loads ranging from 25kN to 55kN.

Cementation moved on site at the end of October 2004 with up to five rigs working from a working platform. It used a combination of a Soilmec R622 and a pair of Junttan PM26 CFA rigs, while Aarsleff opted for a Banut 700 and a Junttan PM20 drop hammer rigs.

The piles are strategically located in singles, pairs and clusters ranging from 8 to 30 piles and in some instances CFA and driven piles are close together.

'Sequencing the manufacture of the precast piles was quite critical to match their installation, ' says Cementation project manager Jonathan Manning. 'Where the precast and CFA are in close proximity, we ensured the precast were driven first, eliminating the risk of damaging newly-cast CFA piles or inducing additional loading.' The precast concrete piles are up to 22m long. Aarsleff drove them to a set through the made ground overlying alluvium to penetrate and found between 3m to 4m into the underlying mudstone.

The CFA piles, which vary in length from 21.5m to 26m, are all founded between 4.5 m and 9m into the mudstone.

Most of the work was completed before Easter but piling was hampered by underground slag which was impossible to drive through.

Aarsleff moved off site while an area that was to accommodate 200 piles (about 20% of Aarsleff's total) was excavated down about 7m to locate and remove the slag. This was replaced with compacted back' ll and Aarsleff returned to 'nish its piling - completed in June.

'The area of fused slag obstruction considerably reduced our progress as we had to wait for excavation, ' says Manning. 'Similarly, where single precast piles have refused and been left upstanding, Celsa's consulting engineer Idom decided whether to remove or abandon them or redesign the affected area.' The main civil works contractor Laing O'Rourke started on site in February and Spanish steelworks contractor Tauxme will follow to erect the building's structural steelwork before installation of the manufacturing equipment. Celsa's new melt shop is expected to employ about 400 staff when it goes on stream early in 2006.

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