Sustainable construction marks new Fens road project
The £80 million A1073 replacement link between Spalding and Peterborough is being constructed over highly variable ground conditions in the Fens helped by the mechanical stabilization performance of Tensar International’s TriAx geogrids.
Use of 130,000m2 Tensar TriAx to mechanically stabilize the sub-base resulted in minimal soil excavation and reduced plant requirements. The inclusion of locally won sand and gravel capping also reduced the environmental impact and lowered imported material costs.
Lee Rowley, Lincolnshire County Council’s senior project leader, commented: ‘In many places the contractor would have been replacing at least 500mm of materials over considerable distances for the full length of the road. As the sections requiring amelioration were extensive, it was more economical to stabilize the fill layer above. By using TriAx, we should also improve long-term performance and reduce maintenance requirements at no greater cost.’
At 22km, the new road is the UK’s longest project in 2009-10, and will bypass the existing, hazardous narrow road that carries extensive local traffic. Originally salt marsh, the area was regularly inundated; current ground levels are between 1m and 2m above sea level, and the high water table and sinking ground still create flooding problems.
Detailed ground investigation by the Lincolnshire County Laboratory revealed 200-300mm of topsoil over around 1-2m of firm alluvial clay across much of the site, overlaying very soft clay and peat layers. In many locations, however, the firm clay crust is deficient or entirely missing, being replaced by loose sand or sandy silt, with additional pockets of loose peat and silt.
The road foundation and pavement structure is approximately 1.1m in thickness, and is designed to be constructed over the ground with as little topsoil removed as possible; the finished road level is 0.5m above existing ground level. Where the clay crust is thin and the base of the road reaches within 0.5m of the base of the crust, the laboratory recommended removal of weak material with a California Bearing Ratio of less than 2, and replacement by granular fill.
Lee Rowley said: ‘This would have meant that half a metre or more of material might have to be removed and, as the sections requiring amelioration were extensive, it was more economical to stabilize the fill layer above.’
The resulting design included removal of 150mm of topsoil, and introduction of a sub-base of 150-180mm of Type 1 imported granite aggregate fill, mechanically stabilized with Tensar TriAx and with a geotextile separation layer. In all, TriAx was used over around half the road length of the single carriageway road, as well as some hard shoulder areas. In areas prone to seasonal flooding, the sub-base thickness was increased to up to 235mm.
Scheduled for completion in summer 2010, the road will provide a faster and straighter link while allowing local traffic to use the older road; there are seven connections between the two roads. The old A1073 road needed frequent maintenance, which was another source of frustration for motorists, which should be alleviated by the modern construction methods.
Tensar International, Cunningham Court, Shadsworth Business Park, Shadsworth, Blackburn BB1 2QX; tel: (01254) 262431
Use of 130,000m2 Tensar TriAx to mechanically stabilize the sub-base resulted in minimal soil excavation and reduced plant requirements. The inclusion of locally won sand and gravel capping also reduced the environmental impact and lowered imported material costs.
Lee Rowley, Lincolnshire County Council’s senior project leader, commented: ‘In many places the contractor would have been replacing at least 500mm of materials over considerable distances for the full length of the road. As the sections requiring amelioration were extensive, it was more economical to stabilize the fill layer above. By using TriAx, we should also improve long-term performance and reduce maintenance requirements at no greater cost.’
At 22km, the new road is the UK’s longest project in 2009-10, and will bypass the existing, hazardous narrow road that carries extensive local traffic. Originally salt marsh, the area was regularly inundated; current ground levels are between 1m and 2m above sea level, and the high water table and sinking ground still create flooding problems.
Detailed ground investigation by the Lincolnshire County Laboratory revealed 200-300mm of topsoil over around 1-2m of firm alluvial clay across much of the site, overlaying very soft clay and peat layers. In many locations, however, the firm clay crust is deficient or entirely missing, being replaced by loose sand or sandy silt, with additional pockets of loose peat and silt.
The road foundation and pavement structure is approximately 1.1m in thickness, and is designed to be constructed over the ground with as little topsoil removed as possible; the finished road level is 0.5m above existing ground level. Where the clay crust is thin and the base of the road reaches within 0.5m of the base of the crust, the laboratory recommended removal of weak material with a California Bearing Ratio of less than 2, and replacement by granular fill.
Lee Rowley said: ‘This would have meant that half a metre or more of material might have to be removed and, as the sections requiring amelioration were extensive, it was more economical to stabilize the fill layer above.’
The resulting design included removal of 150mm of topsoil, and introduction of a sub-base of 150-180mm of Type 1 imported granite aggregate fill, mechanically stabilized with Tensar TriAx and with a geotextile separation layer. In all, TriAx was used over around half the road length of the single carriageway road, as well as some hard shoulder areas. In areas prone to seasonal flooding, the sub-base thickness was increased to up to 235mm.
Scheduled for completion in summer 2010, the road will provide a faster and straighter link while allowing local traffic to use the older road; there are seven connections between the two roads. The old A1073 road needed frequent maintenance, which was another source of frustration for motorists, which should be alleviated by the modern construction methods.
Tensar International, Cunningham Court, Shadsworth Business Park, Shadsworth, Blackburn BB1 2QX; tel: (01254) 262431
