The first stage of the 60ha commercial and leisure complex was to widen the embankment of Humberside County Council’s Priory Way spur road.

The original embankment, built out of PFA ten years previously, had experienced consolidation coupled with settlement due to the weak underlying soils which comprised of soft alluvium over river gravel and Welton chalk. The problem was exacerbated by lateral movement at the bottom of the embankment’s edges where material had rotationally slipped outward. If the embankment were to be widened with PFA or ordinary granular fill, the level of further settlement was predicted to be as much as 500mm, compared to 50mm with Fillmaster blocks and topsoil. The engineers also considered that EPS would provide a better overall profile of total settlement compared to PFA.

With the decision to use Fillmaster, 300mm of topsoil was removed and a stepped excavation was carried out with a bench height of 610mm by 1220mm wide. Blocks were benched in position following the use of a sub-base of Type Two granular material and a 50mm sand blinding to act as a drainage layer. Four different grades were required and were clearly colour-coded to avoid any confusion. The highest at 30kg/m3 was employed in areas required to take the greatest weight immediately beneath the road pavement. The blocks were pinned and covered with a polyethylene membrane as protection against fuel spillage. A thin sand layer, followed by a selected fill, completed the embankment.

Where the embankment was tightly curved, blocks were customised to fit by cutting and shaping with a hot wire. Little plant was required and only six people were employed in the gang.

 Client: Henry Boot Developments
Consulting Engineers: Hannah Reed and Associates, Doncaster
Contractor: Birse Construction, Barton-on-Humber
Volume: 6,300m³