The Avče pump storage scheme has a turbine capacity of 185MW. The lower reservoir is formed by the river Soča, with an associated upper reservoir 520m higher, sited in a natural depression. The ground under the reservoir is calcareous, formed of karst formations, so the reservoir had to have an impermeable lining system.

After the initial earthworks and concrete structures were constructed, WALO commenced the lining works. The works consisted of an Asphaltic Binder Layer (ABL) and bituminous Dense Asphaltic Concrete (DAC) layer, the first project of its kind in Slovenia. Like every WALO project, the team applied DAC formulated to a unique design mix using specialised laying and compaction techniques.

To comply with the rigorous required Quality Assurance regime, WALO installed its own asphalt laboratory at the mixing plant to control the quality of the asphalt. During the lining works the WALO team alternated the placing of the different materials throughout the project, dependent upon the prevailing weather conditions. This degree of flexibility enabled the optimization of the scheduling of the works. All works – including joint construction, ramps and access roads and mastic coating, a total area of 140,000m² – were completed after only four months.