3D confinement system offers stable vegetated cover over steep soil-nailed slope
Albion Drilling Group Ltd. was employed by project contractor, Safedem, to stabilize and encapsulate an existing steep embankment situated along the River Don in Aberdeen, Scotland. The project objective was to stabilize a volatile embankment with soil nails and then install a 24 in. thick encapsulation layer consisting of both stone and top soil. The encapsulation layer would be held in place through the use of rock fall netting. Covering the encapsulated topsoil/aggregate layer and keeping it stable, as well as aesthetically pleasing, presented the biggest challenge.
United Kingdom geosynthetics supplier Greenfix UK was provided the original site drawings for review and to solicit their recommendation for ensuring the embankment remain stable in this popular tourist area. Greenfix UK offered a value-engineered solution that changed the original design of two layers of a thinner cross-section, geotextile-based confinement system to one layer of 12 in. deep 3D geocell material (Presto Geoweb). The complete solution recommendation included high-strength tendons and tendon load transfer devices to provide additional stability.
The 3D confinement system was chosen to provide a soil retention cover over the encapsulated layers, creating a visually-appealing and stable vegetated embankment at this high-profile location. The goal was to hide the structural slope support system with natural vegetation protected from potential erosion issues.
Greenfix UK’s technical team proposed a suitable stake anchorage pattern for the system to supplement the tendon/tendon clip anchorage. Site support also was provided to Albion Drilling to ensure that the installation proceeded smoothly.
Special tendon load transfer devices transfer slope gravitational forces from the cell wall to the high-strength tendons. They connect and lock securely through the cell walls, allowing for pre-assembly at the top of slope.
Assembling the tendons and tendon load transfer clips was performed at the top of the slope. Each pre-assembled section was secured at the crest and stretched down the slope. Pre-assembly minimized worker time on the steep slope and reduced the risk of accidents. Subsequent sections were expanded, aligned with adjacent sections, and attached with polymer, weather-resistant connection keys. The connection of all panels created a contiguous slope cover that was ready for topsoil infill.
Infilling operations were performed from the top of the slope by dropping topsoil from a bucket loader. Crews lightly tamped the infill evenly in place within the cells. Once fully infilled, a mix of natural flowers and indigenous vegetation was sprayed over the surface and covered with an erosion control blanket, protecting the seed from washout prior to establishment of vegetation.
- Angle: 1.2H:1V
- Length: 32 ft
- Vertical Height: 20.5 ft