Dan Y Lan Landfill Slip, Pontypridd, South Wales
Client: Dawnus Construction working for Rhondda Borough Council
Project Brief: Since 2004 a series of partial slips had created safety problems lower down the slope.
The Solution:The geotechnical issues were solved using Tensar grids. The finished slope was 36 degrees, 40 metres in height and 60m wide. 250mm depth of topsoil was required, rather than the nominal 50-75mm, as cover for marginally contaminated on site fill material. Salix installed a series of dead Willow Faggots at 1.5m spacing down the slope in order to physically retain the 250mm of soil cover. Willow Faggots are a more environmentally sustainable alternative to cellular confinement systems and are easier to fill. The area was then covered with 250mm of soil using long reach machinery. Salix then covered the 4000m2 face with HydraCX2, a hydraulically applied erosion control solution. The product is cotton fibre and straw based with additional polyacrylamides which is a water-soluble compound used to minimise soil erosion by binding the soil particles.
The Result:The cotton and straw fibres interlink to give an effective protective covering over the soil. The product was selected because the fibres would conform better to the irregular slope profiles than a coir blanket alternative, giving a higher level of erosion control. The germination and establishment of vegetation was rapid with no surface erosion, even after a number of 3 inch rainfall events and the wettest August on record.
Materials used: Willow Faggots HydraCX2 with site specific seed mix
Overall view of landslip Feb 2004
Placement of dead Willow Faggots along length of slope
HydraCX2 being applied to the slope surface
Vegetation establishment after 24 days with no
surface erosion despite a number of 3 inch rainfall events
Vegetation establishment after 70 days
Close up shot of legume rich reclamation mix used for poor quality soils
