Digestion Tank Infill | Luggie Glen, Scotland



Digestion Tank Infill for sewage and waste

A solution for the reclamation of land at a former sewage treatment works benefited from the use of Leca® Lightweight Expanded Clay Aggregate which was used as backfill for disused concrete sewage digestion tanks, during the scheme to reclaim the brownfield site and develop a new business park.

Working on behalf of North Lanarkshire Council, Edinburgh; based Soilutions Ltd and consultant, Jacobs, devised a BET – Best Environmental Technique – approved solution which involved the excavation and disposal of the contents of five tanks, including sludge and old fill.

Two of the tanks, measuring 12 metres in diameter and nine metres deep required a lightweight fill to mitigate the risk of movement from backfill loadings.

Environmentally-friendly Leca® Lightweight Expanded Clay Aggregate, which has a density just a seventh of the equivalent volume of traditional hardcore, was specified for its ability to provide an effective fill, requiring only minimal compaction.

The one metre thick tank walls, which were mainly buried underground with just one metre protruding above, were broken back to approximately 500mm below existing ground level, prior to backfilling with a total volume of more than 2,000m³ of Leca® Lightweight Expanded Clay Aggregate. The material was placed in layers of one metre in depth using a long reach excavator, with each layer being tamped down using the mechanical bucket, before the installation of the next layer.

After backfilling to the existing ground level, a geotextile waterproof membrane was placed over the area, followed by a 250mm layer of imported topsoil. Each area was then planted to blend in with the surrounding wooded area.