Lagoon embankment stability improved thanks to lime stabilisation technique27th Apr 2018

A lime stabilisation technique used by Jones Bros Civil Engineering UK played a significant role in re-building an anaerobic digestate lagoon.

The family firm was called to the anaerobic digestion plant in Lincolnshire, after one of the embankments on the 100m x 40m lagoon showed signs of distress. This was caused by a combination of the existing material used to construct the lagoon along with the steep angle of the embankment.

Based on technical, engineering, and economic reasons, lime stabilisation of the existing material was selected. This improved the strength of the material used in the embankment and, importantly for client, the design and technique allowed maximum benefit from the land available.

Jones Bros’ work also included re-landscaping of the surrounding area, installing a drainage system, reinstating the base of the lagoon with 2mm high density polyethylene (HDPE) geomembrane, installing a 1mm geomembrane cover, and reinstating a short track for access to and from the lagoon.

Sion Dolben Hughes, site engineer, said: “The California bearing ratio (CBR) results, which measures the strength of natural ground, subgrades, and base courses, showed that there was a significant improvement in the strength of the embankment. Shear vane testing also took place and showed a considerable improvement on the sheer strength of the embankments.

“Our work on the lagoon consisted of removing about 300mm of spent digestate (the out-turned product from the on-site anaerobic digestion plant), removing the existing plastic geomembrane, and deconstructing the existing embankment.

“A matrix of 160mm HDPE pipes were installed to the base of the lagoon for the purpose of agitation. This allows the client to circulate the digestate through the network of pipes to rotate the spent digestate to avoid the suspended particles from settling and solidifying on the base. In addition, the pipework enables the client to extract the spent digestate material, which is then spread over agricultural land as a valuable fertiliser.

“We also re-instated security fencing surrounding the lagoon, top soiled the surrounding areas, and re-instated a small track to allow access to and from the lagoon. In addition, we re-installed gabion baskets along the front of the site.”

Jones Bros had nine people on site at the peak of the project, including Islwyn Williams the site manager, a site engineer, plant operatives, and labourers.

Sion, who has been with the civil engineering company for nearly six years, added: “The team did a fantastic job to provide a high-quality solution for the client who was very pleased with the outcome.”

Founded in the 1950s and employing almost 350 people, Jones Bros is working on contracts in sectors including the construction of waste management facilities, highways, flood and marine defences, and renewable energy projects around the UK.