THE PROBLEM
New access required to open up the former Crindau coke-fuelled gasworks for a new retail store. Variable ground conditions with the potential for differential settlement.
THE SOLUTION
Tensartech TW3 wall system for the approach ramp retaining walls and bridge abutments were chosen for a new carriageway into site. Tensar TriAx® geogrids were also used to stabilise the abutment foundations adjacent to transition zones.
PROJECT DESCRIPTION
Tensar geogrid technology has been used to solve earth retention and extensive ground stabilisation problems encountered in Kier's development of a major new supermarket. Located on the former Crindau coke-fuelled gasworks close to the banks of the River Usk, the project needed to be completed before the 2010 Ryder Cup. Access to the store is provided by a new carriageway off the main A4042 road which is 9 metres above the store car park level and is connected by a 25m long road bridge. Tensar proposed a BBA-certificated Tensartech TW3 wall system featuring uniaxial geogrids, faced with the attractive dry laid, modular blocks for the retaining walls and bridge abutments, which were 6m high at the western end.
At the eastern abutments, between the ramped walls over a transition to alluvial soils, layers of Tensar TriAx® were installed beneath granular capping material to improve load bearing performance and mitigate differential settlement, by creating a transition zone to a pile supported concrete slab. The underlying ground consisted of alluvial river soil deposits, a shelf of bedrock at the western corner which slopes sharply down towards the east and extensive made-ground on the old industrial site.
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.
’’There were a number of potential differential settlement problems on the site due to the extremely variable bearing capacity of the ground with extensive transition zones,‘’ commented James Bee, Project Manager for Kier.
’’The Tensar geogrid solutions saved us up to 8 weeks of 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 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”.
