Basal Drainage & Slope Retention

Pozidrain and Erosaweb - Shetland Gas Plant, UK

Client Total E&P UK


Consultant Sir Frederick Snow & Partners

Erosaweb Geocell



– Replaces drainage stone layer, maximising the void space of the cell
– Wide width rolls for rapid installation
– Simplified construction speeds up installation, reducing costs
– 120 year design life for long term assurance

Project Description

The Shetland Gas Plant (SGP) represents a £2.5bn investment by TOTAL to service the Laggan and Tormore gas fields, located 125km to the north-west of the island. The Department of Energy & Climate Change estimated that these fields account for 17% of the UK’s remaining oil and gas reserves, and so are essential to future energy security.

The site of the SGP was covered by a peat bog totalling some 700,000m³ in volume, and which had taken several thousand years to form. It was a condition of the Scottish Environmental Protection Agency, the Scottish Islands Council and Scottish Natural Heritage that the peat be preserved for reinstatement following the end of life decommissioning of the site. The solution was to build a 500,000m³ peat store, and later a second 200,000m³ store, into the terraced slopes of the site.

The Challenge

The design of the peat stores was to mimic, as far as possible, natural peat conditions. The stores were to be open-topped, to allow rainwater to percolate through the peat, with drainage from the side and base as a peat bog would do naturally.

A traditional stone drainage layer would have required the import and placement of many thousands of tonnes of quarried stone, increasing the size of the stores and the extent of excavation requirements to allow for the volume of the stone as well as the peat.

The Solution

The designer approached ABG for a drainage solution to be compliant with the development restrictions to facilitate this ambitious project. The inclusion of Pozidrain 12S500/NW8 geocomposite drain in place of a traditional stone drainage layer enabled the maximum void space to be utilised for peat storage rather than drainage stone, and so kept the footprint of the stores to a minimum.

Erosaweb GWX 150/300 geocell was used on the 1:2.5 slopes to reinforce the soil veneer. This used around 10,000m³ of the excavated peat, providing a native environment for local flora and fauna and reducing the quantity placed into storage.

Pozidrain drainage geocomposite and Erosaweb geocells have a 120 year design life, so performance is assured far beyond the anticipated operational lifespan of the SGP.


The ABG Service

ABG provided design and technical support, enabling the designer to propose the most cost effective build solution.

Contact ABG today to discuss your basal drainage and slope reinforcement project specific requirements and discover how ABG’s experience and innovative products can help.

Additional information