Barbadoes Wood Stabilisation
In January 2008, a landslide took place in the Forestry Commission Wales’ (FCW) Barbadoes Wood plantation on the western slopes of the Wye valley above Tintern Abbey, resulting in the temporary closure of the A466.
Initial emergency works were carried out by FCW. Further geotechnical study confirmed the nature of the instability and determined the preferred remediation solution. The main elements of the scheme, carried out by Dean & Dyball comprised:
- Some 500 soil nails to reinforce the slopes within the landslide, together with meshing and erosion protection. The original design for the soil nails required a length of rock embedment depending on the pre-ceding length of overburden drilling. This process was started, but aborted due to the excessive amount of grout being used. Dean & Dyball were extremely proactive in sourcing an alternative soil nail anchor design, which was arrived at by increasing rock embedment length to 4.5m and only grouting this section.
- Minor earthworks to reduce loads on the head of the landslide, and rationalise adjacent existing slopes. The very steep, uneven and slippery conditions made access for men and machinery extremely arduous, especially for the drilling operation. Several solutions were employed including cutting platforms into the hillside, belaying excavators on winches and using special ‘walking’ excavators.
- Drainage improvements to civilise surface flows and reduce surface infiltration into the landslide. Clay lined channels were constructed using clay won from the wood.
- Restoration of masonry walls adjacent to the A466 were disrupted by the landslide. Head walls for culverts and stone cascades were constructed from site won stone.
- Meshing and erosion protection to the debris slide track.
- Landscaping, vegetation restoration and grass seeding. To minimise operatives presence on the steeper slopes a seeding/erosion product was administered using cannons.
Given both the steep terrain and the environmental setting, particular emphasis to health and safety and environmental aspects were needed throughout this scheme. This was a very successful project carried out by a local directly employed staff who worked well under difficult conditions.
Local MP David Davies said: “I am delighted with the remedial work done in Tintern, Forestry Commission Wales and the contractors are to be congratulated on an excellent job well done. ‘Giant Nails’ up to 60ft long have been hammered into the hillside and secured with heavy netting to keep the soil in place. Surface water has been channelled through the hillside in a way that limits the possibility of further mishaps. Whilst nobody can ever guarantee there will be no future incidents the engineers are all fully confident they have done a great job. From my vantage point on the hillside the works looked most impressive to me.”