Expanded clay aggregate from maxit has provided a lightweight solution for a new road embankment in Cardiff. Groundworks contractors at the site of a new international sports village are building a slip road over a former refuse tip – land prone to settlement.

The £700 million Cardiff International Sports Village is being built on a former harbour and industrial site contaminated by hydrocarbons and deep in domestic refuse.

Consultant engineers Arup, who earlier developed a remediation strategy for the whole 35-hectare site, were engaged by Laing O’Rourke, main contractors for a £15 million infrastructure project, to devise a scheme for the construction of new roads at the former landfill site.

An embankment on top of land composed of soft alluvial clay with a layer of tipped domestic refuse above was required for a new slip road linking to an existing high-level carriageway.

By using maxit LWA lightweight fill, Laing O’Rourke were able to limit the depth of excavation required, avoid heave on the surrounding ground and ensure that future settlement is within the limits determined in the strategy developed by Arup.

The existing ground was excavated prior to the installation of  some 12,000m³ of maxit LWA in 10-20 mm grade to replace the excavated material and to raise the core of the new embankment within earth bunds.

The material was delivered in 5,000m³ capacity ships to nearby Newport, then transported in 50m³ high-sided tippers for loose tipping on site. Because of the light weight of the LWA – one seventh that of traditional fill with an average dry bulk density after compaction of just 310 kg/m³ -- movements of the 50 m³ high sided delivery tippers were drastically reduced.

Prior to installing the first 150 mm layer of maxit LWA, a gas membrane was installed along with venting to ensure efficient release of ground gases from the former tip. Geogrid was then laid prior to tipping of a further 300 mm of LWA, which was compacted and covered by a further layer of geotextile to contribute to good stability of the embankment over the soft ground.

Further one metre layers of LWA, compacted by passes of a tracked vehicle, were then laid to the required level, followed by a further layer of geogrid and the various road construction layers.

The cross section of the embankment varies along its length to produce a pattern of imposed loadings. These will mean acceptable settlement for both total and differential values.

Maximum settlement is predicted in the range 150-200 mm with differential settlement to gradients of 1 in 50 or less, for the long term design life of the road.

Scheduled for completion in 2010, Cardiff International Sports Village will transform the site in Cardiff Bay to provide sports, leisure, commercial and residential and arts facilities. Sports provision will include ski slopes, an ice hockey stadium, gold, cricket, rugby, football and water sports facilities.