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Blackpool rock helps Balfour build UK's largest sea defence project

Defending the Fylde peninsula from whatever the Irish Sea can throw at it required Balfour Beatty to take an innovative approach to coastal engineering.

Project: Rossall & Anchorsholme Coastal Defence Project
Client: Wyre Council, Blackpool Council & the Environment Agency
Contract value:
£90m
Region: North-west
Main contractor:
Balfour Beatty
Lead designer:
CH2M
Start date:
April 2014
Completion date:
August 2018

The Fylde peninsula, which stretches for more than 21 km from Morecambe Bay in the north to the Ribble estuary in the south, has been a magnet for tourists since the early 19th century.

It includes Blackpool’s famous piers, fish and chip shops, Pleasure Beach and illuminations, as well as Fleetwood, which was built as one of the UK’s first planned towns in the 1830s.

The seafront and its surroundings are home to a population of more than 250,000 people.

And while facing the Irish Sea has helped to make the area historically one of the UK’s leading seaside holiday destinations, it has also provided its fair share of challenges.

The area’s infrastructure has struggled to cope with recent weather extremes, which saw Blackpool’s promenade battered by 145 kph winds and submerged by particularly rough seas in winter 2014.

But now Balfour Beatty is looking to update the Fylde’s ageing defences in what is the largest sea defence scheme currently under construction in the UK.

By the seaside

The contractor’s Fylde Peninsular Coastal Programme is designed to protect 12,500 homes across a 2.7-km stretch of coastline between Anchorsholme in the south to Rossall in the north.

The project will protect the area from a one-in-200-year storm event, and has a planned design life of 100 years.

It’s no small feat to provide that level of protection over such a large area, while also providing an enhanced seafront for the local population – which is why three local authorities clubbed together with Balfour Beatty to deliver the project.

Balfour Beatty Rossall Anchorsholme sea defence 5

Balfour Beatty Rossall Anchorsholme sea defence 5

The combined schemes at Rossall and Anchorsholme are the UK’s largest current sea defence project

The region, and particularly Rossall, had seen significant flooding in the 1920s, 1930s and 1970s, which encouraged the local authorities – Wyre, Blackpool, and Fylde – to work together to shore up the seafront against any future storms.

This started with a major promenade and sea defence project stretching from Blackpool to Cleveleys, which was delivered by Birse Civil Engineering – now part of Balfour Beatty.

The scheme covering Anchorsholme and Rossall, which sits adjacent to the scheme in Cleveleys, is being delivered as one package, despite being two separate contracts – Anchorsholme is with Blackpool Council while Rossall is with Wyre.

Balfour Beatty won preferred bidder status for both schemes in 2012, and worked closely with the councils, as well as the Environment Agency, to work up a scope for the development.

A £90m funding package was secured in 2013, including the project’s overall construction value of around £75m, and Balfour Beatty secured the contract in October 2013, allowing the contractor to start on site in April 2014.

And although both schemes will be delivered together, they have subtly different requirements.

Two jobs in one project

At Anchorsholme, which is worth £20m, Balfour Beatty will fully replace the existing sea defences, which were built in the 1930s, and improve access to the foreshore.

Balfour Beatty project director Simon Barker explains that the current defences are “crumbling and well beyond their design life”.

“Some of the wall at Anchorsholme was in such poor condition that a chunk of concrete weighing around two-and-a-half tonnes was dislodged in the winter storms in 2013,” he says.

Some of the storms in 2013 and 2014 were so extreme that the promenade ended up under water, he adds.

Source: Balfour Beatty

All this underlined the need for major improvements along Anchorsholme’s 910 m coastal frontage – and led Balfour Beatty to install the new defences seawards of the existing 1930s sea wall.

Mr Barker says this meant the contractor could keep the existing defences “largely intact” while building the new defences, which reach 1.6 m higher than their predecessors, keeping the local area protected throughout the construction period.

The new fortifications are primarily a precast solution, using a high-quality concrete mix designed to have both maximum abrasion resistance and an attractive finish to improve the aesthetic of the seafront.

A decision was made early in the process to use precast concrete at both schemes, Mr Barker explains.

“Going back a long way, there were quality, cost and risk benefits for doing the scheme precast, which outweighs doing it with in-situ poured concrete.

“You’re trying to minimise any in-situ [concrete pouring] in that tidal zone, for all the obvious reasons.

“An artic carries 28 tonnes, so we’ve designed the [precast] units to be 14 tonnes each”

Simon Barker, Balfour Beatty

“The finish we have on the precast units is fantastic, and even with the best concrete in the world you wouldn’t get the same with an in-situ poured product.”

He adds that the team has been developing its ideal concrete mix over a long period of time to ensure the best quality precast for the scheme’s 100-year design life.

“Through work that we’ve done previously at Cleveleys and Blackpool, that mix has evolved using different aggregates and properties within the concrete,” he explains.

Throughout the project’s design life, the precast units are only allowed to wear away by 70 mm.

“We’ve done a lot of testing working with Salford University in terms of abrasion resistance – the more resistant to abrasion you make the mix, the more you can slim down the [precast] sections and reduce the cost.”

He says the mix has been constantly evolving, with different innovations used to achieve maximum efficiency – as well as an attractive finish to the precast units.

“We’ve gone from concrete with finer aggregates in it, to micro-silica, to micro-silica with granite, and now we’re using a limestone from a quarry in Northern Ireland. Although it’s a limestone, it has better abrasion-resistant properties than the granite,” he says.

Concrete innovation

The approach to making the seafront and promenade an attractive public asset also includes using fibres in the concrete.

Using fibre removes the need to use rebar in a tidal environment – and with it the potential of rusting rebar staining the concrete and ruining its finish.

And the precast units have also been designed with efficiency in mind.

Balfour Beatty Rossall Anchorsholme sea defence 8

Balfour Beatty Rossall Anchorsholme sea defence 8

Each precast unit weights 14 tonnes

The units were installed via two 180-tonne crawler cranes, but the designs were altered to minimise the amount of transport needed, Mr Barker explains.

“An [articulated lorry] carries 28 tonnes, so we’ve designed the units to be 14 tonnes each – that means we can get the maximum out on each haulage,” he says.

He adds that making the units slimmer made them wider, therefore covering a larger area and reducing the total number of units needed.

To build the defences, the team installed a sheet pile 2 m below beach level, which forms the lower cut-off and the toe of the structure.

An in-situ poured concrete capping beam was then installed, followed by the precast units, which formed a sloping revetment and stepped wave-breaker units.

The revetment units are 450 mm thick, with 50-75 m grouting and 200 mm of blinding concrete underneath, making the defences around 700 m thick in total.

Above the revetments, the wave wall, again precast, was then installed, which links to the promenade – completing a 12 m-high structure that is 24 m long from toe to rear.

The original highway behind the sea defences has also been raised to allow direct access from the nearby Anchorsholme Park to the promenade.

“It’s an enhancement in terms of public accessibility and real enhancement compared to what was there before, and it makes a much more robust sea defence in terms of height and scale,” Mr Barker adds.

Ready to rock

At the second part of the overall scheme at Rossall, the team has adopted a slightly different approach.

Rossall is the larger of the two elements that make up the coastal defence programme in terms of both length and value, with the project stretching for 1.9 km and coming in at £53m, compared with 0.9 km and £20m at Anchorsholme.

The defences at Rossall are also 57 m wide – almost twice the width of Anchorsholme – and 14 m high from top to bottom.

It also differs from Anchorsholme in that it is a hybrid scheme, using not just precast elements, but also a substantial amount of primary rock.

“There’s no point in creating a [specification] of a rock that you then can’t import”

Simon Barker, Balfour Beatty

Being further north, the land around Rossall suffers significantly more abrasion than in Anchorsholme, meaning that the lower part of the revetment structure is made of rock, while the upper part is made of precast concrete.

The Rossall scheme also has significantly more in-situ concrete pours, with 28,000 cu m poured throughout the course of the project.

Balfour Beatty Rossall Anchorsholme sea defence 6

Balfour Beatty Rossall Anchorsholme sea defence 6

The rock armour for the scheme is locally sourced

The key difference between the two schemes is the rock armour, with over 274,000 tonnes needed to build both the lower part of the revetment and 18 groynes.

The sea wall structure begins 2.5 m below beach level in a similar fashion to Anchorsholme. But before the precast units, there is a lower layer of rock, with each weighing between 300 kg and 1.5 tonnes, with a geotextile above followed by rocks that weigh 2.5-10.5 tonnes.

British made

While it may look relatively simple, building a structure of this type requireed precise planning in terms of the materials used and how it is installed, Mr Barker says.

He explains the team worked closely with the designers to make sure Balfour Beatty could get exactly the right material they needed for the job.

“We wanted to get something that the defences needed, but [which was] also based on what material was available,” he says.

“There’s no point in creating a [specification] of a rock that you then can’t import, or import efficiently.”

This approach led the team to choose rock that was available in the UK, making it both easier and more efficient to get the material needed (see box).

“Traditionally, we could have done a large rock armour that would have forced us to go out to Scandinavia to [source], which would have added a huge amount of risk and cost on to the scheme,” he adds.

Blackpool rock

The rock for the scheme is sourced from 12 quarries in the north of England and in Wales, which provides the most cost-effective solution for the job.

Stone is transported from these quarries on steel-bodied articulated wagons, weighed, and then transported to site.

To maintain site safety when it arrives, the team has developed a system to offload and sort the rock, using two-way radios to make sure no banksmen are present in the working area.

Each piece is offloaded and weighed using a grab mounted on the end of an excavator.

The weights are then recorded, and the rocks sorted into stockpiles of different weight grades on the foreshore before they can be used.

Throughout the course of the 212-week scheme, 50,000 individual pieces will be delivered and offloaded in this way.

Mr Barker says the team has used a number of innovations to control the supply of rock armour throughout the scheme, including drones and GPS.

Operators used drones to inspect each stockpile and record which material had been used and where, further employing them to inspect the groynes that stretch out into the sea from the beach.

Innovation also extends to the team’s installation of Rossall’s precast units, which have been installed using a vacuum lifter.

Vacuum packed

These vacuum lifters allow each of the project’s 2,762 precast units to be installed quickly and safely, with the added benefit of maintaining the scheme’s aesthetic throughout.

“Because of the suction, we don’t [need] any lifting points [in the precast units],” Mr Barker says. He explains that this means the team does not have to “make good” any part of the precast unit once it is installed “You drop it in, you grout it, and you’re done,” he adds. 

Balfour Beatty Rossall Anchorsholme sea defence 7

Balfour Beatty Rossall Anchorsholme sea defence 7

Vacuum lifters have been used to install the precast units

BIM has also been used on the project, which Mr Barker says is the first time that it has been used on a sea defence project of this scale in the UK.

For an asset that will degrade over time and has the potential to be damaged by extreme weather, using BIM was particularly important, he explains.

“We wanted to make sure [the model] was usable and useful to the customers in the future for managing their asset,” he says.

“We’re not just building a big wall; it’s about creating an enhancement to the area as well”

Simon Barker, Balfour Beatty

“If there was any storm damage, for example, we could go into the model and get the casting records of any individual element [of the sea wall], and replace it.”

The Rossall scheme also has a split-level promenade with precast steps taking pedestrians from one level to another – all of which makes the beach and promenade easier to access.

It’s this approach that is the defining theme of the entire project; a civil engineering scheme designed not just to protect people from harm but to also substantially improve where they live – a fact not lost on Mr Barker and the team.

“We’re not just building a big wall; it’s about creating an enhancement to the area as well,” he says.

With work set to complete in 2018, Balfour Beatty looks to be well on course to fully modernise the area’s famous seafront – while keeping residents protected from whatever extreme weather the future might hold.

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