Project Description
Gyproc, part of the Saint-Gobain Group, is Ireland’s largest producer of plaster and plasterboard. Manufacturing in Kingscourt, Co. Cavan, waste from the plasterboard manufacturing process was disposed of in landfill over a number of decades, in line with the facility’s Industrial Emissions Licence. Landfilling at the site ceased in 2009, and a permanent capping system was required in order to provide safe containment of the waste.
The Challenge
The landfill closure project involved the re-profiling of the existing landfill in order to create regularised slopes of up to 1:2.5 (21.8°) and the installation of a permanent capping system over an area of approximately 6.5 hectares. At the time of cessation of filling operations, the overall composition of the waste was estimated to be 95% plasterboard and 5% gypsum residue. The waste was considered to be hazardous and would be soft in places underfoot. The proposed capping system comprised a number of elements: a 200 mm blinding/regulation layer, a gas collection geocomposite, a geomembrane liner, a subsurface water geocomposite and finally a 1m topsoil/subsoil layer. The geocomposites needed to be carefully selected to address the build up of flammable gas underneath the liner and to ensure adequate subsurface drainage, whilst also being stable on the steep slopes.
The Solution
Working with consulting engineer RPS, ABG approached the selection of a suitable drainage geocomposite from first principles. This involved establishing the permeability of the cover soil in relation to the infiltration rate, and calculating the required in-plane flow of the geocomposite when tested with soft foam platens, as per EN ISO 12958. Appropriate reduction factors and a global factor of safety were applied to establish that Pozidrain 4S250D/NW8 geocomposite would provide adequate drainage to ensure stability on the steep slopes.
Pozidrain utilises an impermeable cuspated core conferring a unique benefit that brings economic savings to projects that have a combination of steep (>12°) and shallow (<12°) slopes. Where the slope is <12° Pozidrain can be used with one geotextile. ABG was therefore able to offer Pozidrain 7S250/NW8 drainage geocomposite with one geotextile as a value-engineered solution for the flatter areas of the capping. Flow capacity is dependent upon gradient, and Pozidrain 7S250/NW8 also provided higher in-plane flow capacity to cater for the lower gradient on these flatter areas.
ABG Pozidrain Drainage Geocomposite
The ABG Service
ABG assisted with subsurface drainage calculations and facilitated site-specific shear box testing to establish the suitability of the geocomposites.
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