A combination of poor ground and a tight footprint has meant a project to build new homes, closely overlooking Panmure Street in Glasgow, needed extra support from a combination of geotextiles.
Main contractor and client St Andrews Homes (Scotland) is developing the land to provide two apartment blocks, but the gentle slope beside the street had to be made steeper to reclaim much needed land. In addition, one of the planning requirements stipulated that the new slope must be landscaped.
As a result, the developer called on consultant Woolgar Hunter, who in turn brought in Maccaferri, to come up with a detailed design for the new embankment. Maccaferri has designed the new 180m long retaining slope using its Green Terramesh units with additional geogrids.
These make the most of the short-on-space site and will provide a firm base for part of the new buildings to sit on.
"One of the tricky things here is how tight the buildings are to the top of the new embankment," says the firm's northern region manager Scott Harvey. "In some places, there's only 1.3m from the edge of the embankment to the centre of the first pile for the apartments."
This embankment is being built up with the pre-assembled Terramesh units, which arrive on site flat-packed. Allma Construction is installing these by pulling forward the front panel of double twist woven mesh and securing the steel brackets to form the 70˚ from the horizontal slope face.
However, Harvey says the mixture of made ground and glacial till (which the made ground typically overlies) on site meant the team had to be selective with which fill it used. He adds that it has been one of the successes of the project in managing to create very little spoil that had to be disposed off site.
An additional 300mm thick layer of topsoil is laid at the front of each unit. This is contained by a biodegradable layer of Biomaxi soil blanket, installed in between the unit and soil at the surface.
For extra support in the weak ground, the new embankment is supplemented by Paragrid 80/15 polyester geogrids laid both perpendicular to the face and transversely (parallel) to the length of the embankment. Harvey says these help create extra strength for the new building by spreading the loads coming down the piled foundations.
Before installing these within the mid-layers of Terramesh, site workers cut out holes in the proposed pile locations. Harvey says although this takes more time during the installation phase, it helps in the long run because it avoids the risk of the grids getting caught and damaging the strength in the compacted unit.
Maccaferri's embankment – worth £60,000 to the company – was due to be completed this month, when the foundations and building work will begin.