An alternative use for stormwater infiltration crates has helped to deliver significant carbon savings for a road project in Glasgow.

The £39.1M Glasgow Airport Investment Area (GAIA) project is expected to stimulate significant economic growth in the region.

The project, which is being led by Renfrewshire Council and jointly funded by the UK and Scottish governments through the £1.13bn Glasgow City Region Deal, includes road realignment; a new two-lane bridge across the White Cart Water; a pedestrian and cycle bridge; and new and improved junctions and connections to existing cycleways and pathways.

Work on site will also provide enabling infrastructure and connections into Netherton Campus, a 52ha site next to the airport. The National Manufacturing Institute Scotland and the Medicines Manufacturing Innovation Centre will also be on the site. The two facilities will be central to the emerging Advanced Manufacturing Innovation District Scotland (Amids), which is expected to create local job opportunities and boost Scotland’s manufacturing sector.

Construction began in June 2019 after Renfrewshire Council appointed Wills Bros Civil Engineering as main contractor to deliver the GAIA project. 

One of the major challenges has been construction of a 1.6km road which crosses a series of 132kV underground power cables. Preliminary proposals to protect these sensitive high voltage assets involved placing a series of steel reinforced concrete beams to span reinforced concrete piles – effectively creating a piled bridge. 

But during the design phase, asset owner Scottish Power raised concerns about the potential for damage to the cables from ground vibrations, such as piling. 

Wills Bros technical manager Graham Lloyd explains that the cables were installed at the site in the 1940s and are located in the soft ground of the floodplain. The site is bounded by two rivers. One of them, the White Cart Water, has a significant tidal range which affects groundwater. 

“We’re dealing with a dynamic groundwater system, so there’s a lot going on in terms of construction risk with earthworks operations. Structurally, the ground is really challenging for engineering purposes,” says Lloyd. 

“The cables provide an electricity supply to a large area of Renfrew and Glasgow, which also posed a significant challenge.” 

There’s a lot going on in terms of construction risk with earthworks operations

To add to the complexity, the cables are oil cooled, so each one has oil running through its core. 

“I had never come across oil cooled power cables before. They’re for high power consumption and quite specific,” adds Lloyd. 

“Initially, we asked if the cables could be moved completely. However, the cost to remove them was prohibitive, so we had to deal with crossing them.”

The original proposal for the project was also carbon intensive. An assessment undertaken during the pre-construction phase found that the initial reinforced concrete proposals had an impact of 1,546.28t of carbon dioxide equivalent (CO2e), which was almost 13% of the wider project’s projected footprint.

“The design would have required significant volumes of concrete and steel reinforcement, as well as the mobilisation of heavy plant. In addition, to get a piling rig to install those piles, we would have had to install a temporary access and working platform so that we could complete the work safely without sinking into the ground. 

“The effects of any settlement of the ground adjacent to the cables due to construction works could also impact on the cables. There are a lot of different elements involved,” says Lloyd.

The contractor worked with engineering firm RPS to explore alternative solutions for minimising disturbance to the sensitive underground assets, as well as prioritising sustainable materials. 

Wills Bros met with Scottish Power to discuss the scheme and proposed an alternative solution that involved building an embankment instead of the piled bridge. 

The storm storage crates have a trafficable capacity, and are designed to go under car parks, for example

But building an embankment on top of the cables would have created extra insulation, inhibiting the amount of heat dissipation from the cables and ultimately affecting the power capacity.

“We started thinking about how we could get air flow to vent through the embankment to offset its insulating effect on the cables. 

“We looked at installing box culvert units, perforated pipes – all sorts of weird and wonderful design arrangement sketches were drafted to find the best solution to provide venting through the embankment which would help to cool the air,” says Lloyd. 

The final design incorporated the use of Wavin Aquacell units, geogrid reinforcement, and lightweight concrete and fill material which minimises self-weight loading and the risk of disturbance during installation. 

Typically used for storage in drainage applications, the Aquacell crates are hollow and created from reformulated, recycled plastic. Each unit is 95% void and designed to hold 190 litres of water. 

In total, more than 6,000 crates have been used for the project. 

“When we presented the design for the lightweight embankment to Scottish Power, they gave us a very fair hearing. Innovation can be thwarted by clients or third party stakeholders because they want to know the solution has been proven elsewhere,” says Lloyd. 

“We explained that our proposal has never been done in this context before, but the engineering is there.

“The storm storage crates have a trafficable capacity, and are designed to go under car parks, for example.

“We could also demonstrate that the embankment would not create a net increase in temperature, so it wouldn’t diminish the electricity supply.”

The original proposals required more than 1,500t of reinforced concrete, but the embankment solution has required just 3t of lightweight concrete. 

The resulting carbon footprint for this design is 196.342t CO2e, which is a staggering 87% lower than the original proposals due to the elimination of reinforced concrete. 

Work on the embankment phase of the scheme started in April 2020. The overall GAIA project is expected to be complete this summer. 

As a PAS 2080 (Carbon Management in Infrastructure) project, close collaboration between the contractor, designer and sustainability team has been key to ensuring carbon was reduced and tracked as the project progressed.

Lloyd says the innovative and sustainable design for the lightweight embankment is characteristic of Wills Bros’ approach to every project. 

The contractor recently reconfirmed its commitment to carbon neutrality through its participation in the United Nations Climate Neutral Now initiative, which aims to encourage organisations, governments and individuals to measure, reduce and offset their emissions.   

“We’re really serious about making a difference with carbon and the way we impose our projects on the environment. The construction industry has historically been criticised for its recklessness when it comes to carbon and environmental impact. 

“It’s great to be part of a company that is really serious about this and not just paying lip service,” Lloyd adds.

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Tagged with: Flood Protection Geotechnical Roads

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