Distribution Access Road | RD Park, Avonmouth, Bristol

Key groundworks to support a roadway serving a major industrial area have benefited through the use of Leca® LWA as a solution to dealing with soft and contaminated land.

The RD Park, Merebank, Avonmouth project, to provide new warehouse units with ancillary offices, was constructed on a brownfield site, which formerly housed chemical and smelting works.  John Sisk & Sons Ltd, main contractors for developers Rosemound Developments Ltd, originally intended to use traditional aggregates and general fill to support an adoptable highway into the site. However, when it became clear that this would produce far greater than desired overall settlements on the soft alluvial clay, THDA Ltd, consulting engineers, of Birmingham, were asked to develop a lightweight solution capable of substantially reducing settlements, which would be easy to install.  THDA Ltd decided that a combination of geotextile/geogrid "carpet" across the sub-formation, followed by the installation of layers of Leca® LWA 10-20mm, would provide a solution capable of falling within the required settlement and loading limits.

The proposal also tied in with the design for the planned remediation of the contaminated sub strata. To improve delivery and reduce environmental impact, the Leca® LWA was shipped into Avonmouth Dock situated just one mile from the site.  Construction sequencing limited the space available for access and just two 55m³ wagons were placed on turnround to deliver approximately 750m³ per day. Once each load was tipped, Hawk Plant working with CODE Construction PLC of Birmingham, the earthworks sub contractor to John Sisk, spread and positioned the material using the blade of a dozer and then completed three or four tracking passes to compact the material, enabling Hawk to both compact and compress the Leca® LWA in minutes, ready for the arrival of the next load. The sub-formation of the new roadway, approximately 500n metres long and 12 metres wide, was prepared; the embankment filled to THDA's design; drainage and ducting installed, all within one month.  The depth of Leca® LWA used along its length was 1.1 metres on average. A total of 7,400m³ of Leca® LWA was installed during the six-week construction programme.  Initial settlement over the first six weeks after placement varied between 15 - 20mm with 90% primary consolidation settlement being completed within six months of placement.  Settlement to date is in the region of 35mm - far less than predicted.  Subsequent monitoring was undertaken during the maintenance period of the road to record any residual settlement.

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