The ambitious Aberdeen Harbour expansion project has used innovative methods to work in the marine environment while reducing local impact.

Aberdeen Harbour was first built in 1136 and has been a fixture in the city for almost 900 years. Much has changed in this time. The existing North Harbour receives around 6,500 vessels annually but now needs to handle larger cargo and cruise vessels than in the past.

This requires more berthage, deeper and stronger quays and much increased lay down area, with the current harbour limited by its 75m wide channel and 165m turning circle.

As a result, the £350M Aberdeen Harbour Expansion Project was born. With scope to expand the North Harbour limited given its location in the heart of the city, the port is being expanded to the south.  

In December 2016 Spanish contractor Dragados won the design and build contract. 

The firm appointed Arup as its designer, and construction began in 2017.

The South Harbour expansion will provide 1,400m of quay at water depths of up to 10.5m, with a turning circle of 300m and a channel width of 165m.

According to Harbour Board project director Keith Young, the harbour  is on a different scale to what is currently there.

The work involves building fixed quay areas, along with two rubble-mound breakwaters each 640m long, with a crown wall on top of the north breakwater. Breakwaters are separated by a 165m wide channel at the mouth of the new harbour. 

The breakwaters are protected by 9,000 precast concrete accropodes – three dimensional star shaped elements which create a void-filled protective structure to absorb wave energy. 

This is a change from the old North Harbour, where the breakwaters – built in the late 1700s and then extended twice in the early 1800s – are solid walls which reflect wave energy. 

“In the expansion, you have a material in the core between 1kg and 500kg in size and that forms the spine of the breakwater,” Young says. 

“Outside that, you’ve got rock armour that’s 1t to 3t in size and outside that we’ve got the accropodes.

The caissons give us heavy lift capacity in the operational phase 

“They form the outer layer with gaps between them to allow some wave energy to come through. Some wave energy is eaten up in that layer, then some more in the 1t to 3t rock and some more in the next layer.”

Weighing between 18t and 36t, the accropodes were made in a factory in the project’s south compound – the biggest automated facility in the world producing these elements. 

Each has to be carefully placed in a pre-planned position using excavators with specialist attachments.

Large concrete caissons will form the quay walls for the closed quay elements. There are 22 caissons on the project – six on the North East quay, eight on the East Quay and the rest forming the South East pier.

The 8,000t caissons were manufactured in La Coruña in Spain and transported by sea to a storage site in the Cromarty Firth before being towed to the harbour and moved into position. They are approximately 50m long, 12m to 15m wide and 15m high.

“The caissons give us heavy lift capacity in the operational phase,” Young adds. “We need to have something that’s an adaptable facility so having the capacity to have large cranes for large project boats was one of the benefits of the caissons.”

The project has not been without its challenges. Dragados left the scheme in May 2020. The contractor reached a mutual agreement with Aberdeen Harbour Board to part ways due to the impact of the Covid-19 pandemic and because of the challenges of dredging rock from the seabed.

At this point, the contractor was about two thirds through the project. It had made progress with the 640m long north breakwater and the installation of caissons – but a fresh excavation approach was needed. 

In total, it was necessary to dredge 2.4M.m3 of material to get the harbour down to the required depth. Where rock was too hard to excavate mechanically Dragados had been using drill and blast.

But this process was complicated by the fact that it is not permitted to set off explosives with marine mammals within 500m. 

As a result, the Harbour Board took on the role of principal contractor for some elements while Dutch firm Van Oord was engaged as principal contractor for the 640m long south breakwater. The firm introduced a new excavation method.

Young explains: “We got Van Oord’s [barge-mounted excavator] Goliath in and ripped the rock and didn’t have to use any explosives.

“Instead of drill and blast then excavate the rock, you put a small bucket on the Goliath excavator and it puts its teeth into the rock and rips it out. It takes time but you haven’t got the impact on the marine environment of using explosives.”

Around 350,000m3 of rock dredged was used either in the breakwaters or for fill material. 

Breakwater work is now substantially complete and out of the water, and the scheme is now effectively a land-based project.

Offsite construction for the caissons was a successful approach, in terms of efficiency and reducing the impact on residents. It was preferable to creating them insitu with sheet piles. 

“You haven’t got the same impact on the local community and marine environment as with, for example, sheet piling work,” says Young. 

“If you’re doing 800m of impact piling and you’re less than half a mile from local residents, that can have a massive impact.”

Other challenges have included the weather, given the project’s location on the edge of the North Sea, and the impact of Brexit which has pushed the cost of materials through the roof.

The need to social distance also posed the inevitable challenges, with subcontractors separated when they returned to site in May 2020 following the first lockdown.

“Every subcontractor installed its own welfare facilities and that separation is still in place so that if Covid does have an impact on one subcontractor it doesn’t impact others,” says Young.

“It’s a challenging project without Covid but we’re fortunate we’ve got a good supply chain and contractors.”

Overall good communication with the supply chain has been key.

“There is a good collaborative feel to a project,” Young says. 

If you’re doing 800m of impact piling and you’re less than half a mile from local residents, that can have a massive impact

“With some of the contractors being local there’s a huge sense of pride in what they’re doing – it’s going to be a benefit to the area. 

“There are lessons in regard to making sure you’re all pulling in the same direction especially over the last 18 months.

“Overall, the biggest part of this is the scale of it. You walk people down to site and the far end of the breakwater and their jaws drop as to the scale of what we’re building.”

Remaining work for next year includes installing a running surface for vehicles to come in and for boats to load and unload, plus a service trench.

Young explains: “This will run round the perimeter of the quayside to put services in. It means that whatever new service we need to install, we don’t need to break up the surface and excavate – we can just lift covers and feed in new pipes take out whatever is redundant.”

The project is scheduled to be fully operational by October 2022.  

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