Mott Mills Sustainable Development wins Green Apple Award

Project: Motts Mill Retaining Wall
Project Design: Costain CH2M
Client: East Sussex Highways
Flex MSE Units: 575
Type of Install: Flex MSE Gravity Wall
Vegetation Solution: Hydroseed

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Gravitas International, specialists in sustainable, environmental products WIN the Green Apple award for sustainable development with Flex MSE on Motts Mill.

Costain chose the Flex MSE system to conduct repair works to an area of carriageway embankment erosion, along a rural road at Motts Mill in Groombridge, East Sussex. The site featured several construction constraints including narrow geometry and a fragile cast iron water main under the road. Furthermore, there are residences opposite the site, with a watercourse at the toe of the embankment as well as an overhead BT servicing cabling in close proximity to the works area. These parameters restricted the use of lifting equipment and heavy machinery, and so East Sussex Highways’ in-house Design and Build Team chose to explore an innovative new solution for the project with improved buildability compared to standard solutions, as well as being quality assured and cost-effective to satisfy the project’s client. This system was Flex MSE supplied by Gravitas International.

Project Achievements

The Flex MSE system design eliminates the use of hard engineering materials in order to promote sustainable development and biodiversity within the local area. The success of the project has led to Flex MSE becoming the standard solution to embankment erosion, retaining walls and headwall repair projects for East Sussex Highways. Once vegetated the patented Flex MSE (Mechanically Stabilized Earth) system will blend seamlessly into its natural surroundings, therefore, keeping this project in line with Costain’s Climate Change Action Plan to lead UK infrastructure into a zero-carbon future by 2035, supporting the Government in meeting their 2050 target.

Design Overview

In normal conditions, the watercourse is a picturesque meandering stream, enjoyed by the locals.
Four retaining wall solutions were considered for the project, each assessed in terms of constructability, long term maintenance requirements, environmental impact, and cost. Of the four options, three were traditional, hard, engineered solutions, namely: sheet piling, gabion baskets and a proprietary precast concrete segmental block system. The fourth option was a vegetated bag-work wall solution named Flex MSE. This was the solution recommended to the client by the East Sussex Highways’ Design and Build team and was ultimately accepted for construction.

The system consists of interlocking plate and bag components which are laid in a brick bond formation. All the materials used are inert and therefore will not result in any pollution to any nearby land or watercourses. Flex MSE promotes biodiversity within the local area, as it accepts almost all types of vegetation, so it is not limited to specific environments. The environmental team at East Sussex Highways chose a mix of creeping red fescue and rough meadow grass for the Motts Mill project, as it would adapt well to the damp and shady environment.

Flex MSE bag sallow for root penetration, unlike conventional materials such as concrete, so they encourage vegetation growth, and the wall becomes stronger with time as the roots act as tensile reinforcement. Furthermore, the units are incredibly flexible meaning they can be installed around any mature trees or awkwardly shaped bedrock, causing far less damage during construction. This extends to structures that are already present, such as culverts or bridge abutments. Using the Flex MSE design also minimises the hydrostatic pressures behind the wall as the system is free draining, and able to withstand unlimited differential settlement.

The units are faster and safer to install than other conventional solutions as they require a limited foundation and can be placed by hand, eliminating the need for large, fuel guzzling site machinery. As many of the East Sussex erosion sites are on narrow, rural roads, this is a huge benefit in terms of ease of access and noise disturbance to local residents.

The retaining wall at Motts Mill has a wall face area of approximately 30. It is therefore estimated that it would take 2 acres of mature forest, or 54 tree seedlings 10 years to capture the same amount of CO as the new Flex MSE wall will. It will also require approximately 2000kg less Greenhouse Gas to construct compared to if a segmental concrete wall had been built. This figure is equivalent to nearly half of a passenger vehicle’s annual emissions or a third of a household’s annual emissions from electricity usage. (For further details on how you can calculate your projects GHG impact, use our GHG Calculator, Click here.)

Using a conventional system such as gabion baskets would have incurred larger construction costs due to the hire of large plant and the excavation of a substantial foundation, as well as increased maintenance costs due to likely repairs to the steel cages which degrade over time in an area prone to watercourse erosion.

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‘’Weare over the moon our system has been recognised and won the 2022 green apple award for sustainable development as it is a huge honour. Our goal is to provide unrivalled and unparalleled support to our customers on their projects, with a focus on high-quality sustainable products that Gravitas International continues to innovate. The Flex MSE system can be built with no minimum height restrictions with the added benefit of saving a staggering 60% in costings including installation when choosing the system over alternative methods like Gabion baskets.

We guarantee our materials will last for 75 years, with a staggering 120-yearstructural design life when installed by a certified team like ours. The bag and plate system is effectively a soft engineered solution which displays the benefits of hard engineering materials, as well as being a safer, cost-effective, and aesthetically pleasing option. It has been a great year receiving the BBA Hapas (British Board of Agrement) certification and now topped of with a Green Apple Award.  said Jacob Sallon, Managing Director for Gravitas International.

The bags have been used on 5 different projects at East Sussex Highways since their debut at Motts Mill in October 2021, all of which have now blended beautifully into their natural environment.

The Green Apple Awards are run by The Green Organisation – an independent, international, non-political, non-profit environment group dedicated to recognising, rewarding and promoting environmental best practice around the world. To encourage the efficient use of resources.

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