Project Description
The Bennadrove Landfill site is located near Stornoway on the Isle of Lewis in the Outer Hebrides. It is managed by Comhairle nan Eilean Siar (CNES) council and incorporates a leachate treatment plant to safely manage household waste from the local residents.
The Challenge
One of the completed storage cells (Cell F) at the Bennadrove Landfill has recently been reprofiled and temporarily covered. The south facing embankments of the cell features a steep (1V:2.5H) 50m long upper slope (including a mid-slope terrace) above an even steeper 20m long lower slope (1V:1.9H). The embankments required stabilisation to prevent potential slope failure, in addition to a permanent capping design to connect to the site’s leachate management system.
The Solution
The steep profile of the south facing Cell F embankments required a multi-layered geosynthetic design that provides a combination of veneer slope stability and drainage performance. The capping design for the upper slopes includes a thick, puncture resistant nonwoven protection geotextile at the base, positioned beneath ABG’s Claymat geosynthetic clay liner (GCL). A layer of Pozidrain G drainage geocomposite is positioned above the GCL to drain the cover soil layers and is designed to provide the adequate interface sheer friction with the GCL on steep slopes.
For the steeper lower slope sections (approx. 28º gradient) ABG proposed a design incorporating two layers of Erosaweb geocells to stabilise the embankment cover soils. The restoration cover is retained within the Erosaweb cells to reinforce the soils against erosion / slips. The Erosaweb panels are tied to two layers of Abgrid geogrid, positioned on top of the Pozidrain G drainage layer and the Claymat GCL and Terrex protection geotextile layers (see anchor trench detail below).
The ABG Service
ABG’s Design Team carried out the complex veneer stability and drainage calculations, combined with shear box testing to provide the sheer friction angles for the interfaces between the multiple layers of geosynthetics, the sub-formation and the cover soil materials. A detailed design document and drawings were provided to the contractor for the layer installation, anchor trench and leachate system termination details. ABG’s customer services team worked closely with CNES to help coordinate the transport of the geosynthetic materials to the remote island location.
