Tensar geogrid technology has been used to solve the extensive ground stabilisation problems encountered in Kier’s development of a major new supermarket in Newport, Gwent, United Kingdom. Located on the former Crindau coke-fuelled gasworks close to the banks of the River Usk, the store project is on track for completion before the 2010 Ryder Cup.
“There were a number of potential differential settlement problems on the site due to the extremely variable bearing capability of the ground with extensive transition zones,” commented James Bee, Project Manager for Kier. “The performance of the Tensar geogrid solutions saved us up to 6 or 8 weeks piling time on site, as well as substantial costs. The versatility of being able to install TriAx™ where extra ground stabilisation is required is of great benefit.
“The underlying ground included the alluvial river soil deposits, the shelf of rock at the western corner which slopes sharply down towards the east along the access side and the extensive made ground on the old industrial site.”
The project was given planning approval at the end of September 2009. Apart from cost, the major constraint was to have the store open to service the influx of golf spectators anticipated for September’s 2010 Ryder Cup at Celtic Manor five miles away.
“One option would have been to pile the whole site; apart from the high cost, this would have taken too long,” continued Jamie Bee. “Instead, we asked Tensar’s Technical team to develop a geogrid-based design solution for the access road and bridge abutments; this meant we only needed to pile under the 7000m2 store itself, the petrol station and one of the abutments.”
The main A4042 road providing access to the store is 9 metres above the car park design level, and is connected by a 25m-long road bridge. To create the 6m-high abutments at the western end of the bridge, where rock runs under the construction, Tensar proposed a BBA-certificated Tensartech wall system featuring uniaxial geogrids and faced with the attractive modular blocks.
At the eastern end of the abutments, to mitigate differential settlement and improve load bearing performance over the transition to alluvial soils, layers of Tensar TriAx™ were used to create a transition zone to a concrete slab over piles, installed beneath capping between the Tensartech abutment and ramped walls.
“The fill behind the abutments utilised Class 6I graded granular fill. Maxit Light Weight Aggregate was installed for the ramped access road at the eastern end to ensure a low weight overburden on the poor strength underlying formation,” added Jamie Bee.
The Tensartech wall system constructed at Crindau features dry laid facing blocks which are firmly connected with Tensar’s unique polymer key to layers of uniaxial geogrids placed within the fill. The Tensartech solution is rapid to build, as it requires no formwork or crane lifts, and a fully-load bearing structure can be installed without waiting for concrete to achieve design strength.
Contractors: Kier with Kier Western
Groundwork: Kier / Smiths of Gloucester
For more information on Tensar Tensartech structural solutions for walls embankments and slopes, and Tensar TriAx™ please visit www.tensar.co.uk and download brochures.
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