Expanding the footprint of the English riviera
Publication: Construction News, 24 July 2008
Journalist: Paul Thompson
Scheme: Brixham fish market extension – phase one
Contract: Design and build
Client: Torbay Council
Main contractor: Dean & Dyball
Contract value: £6 million
On the Devon coast contractor Dean & Dyball is halfway through a project to extend one of England’s busiest fish markets.
Brixham, one of the triumvirate of towns that make up ‘the English riviera’ on Devon’s south coast, has a past that belies its sleepy status as home of holidaying pensioners.
It may not look like it now at the peak of the season but the town so beloved of the blue rinse brigade is actually the site of an invasion of a totally different colour.
Dutchman Prince William of Orange chose Brixham as his foothold to land his army and launch a bid to oust the Catholic King James II in 1688, a successful quest which saw him crowned King William III.
And now some 320 years later it is a slightly more genteel Dutch invasion, as befits the calm waters of Torbay that could help Brixham stay ahead of the other harbour towns in the south-west.
A busy harbour
Brixham boasts a large, active fishing fleet and one of the busiest fish markets in England. Now Torbay Council wants to increase capacity at the market by constructing a new jetty and providing an extra market hall with new office space.
Dean & Dyball project manager Simon Wilkinson is skippering the bid to net the town the extended fish market and is using steel sheet piles, rescued from use at a railway station expansion project in the rather more hedonistic tourist town of Amsterdam, to help.
“About 75 per cent of the piles are recycled. We got them from Holland and they had been used in various projects including some from the temporary works at Amsterdam Central Station,” he says. “Now they are being used as the walls for the new jetty.”
That new jetty will provide the fish market with somewhere in the region of an extra 4,500 sq m of space. More than enough to provide the new market hall which will enable both the white fish most often landed here – pollack, cod and whiting – to be processed separately from the ‘black fish’ that are also landed.
These include ink-carrying cuttlefish and the two will need to be processed separately when new fisheries legislation is introduced. These regulations have helped kick-start the two-stage development into action.
Phase one – a £6 million design and build project won by Dean & Dyball, will see the contractor build the jetty ready to house the new market hall. It is timetabled to be completed by the end of October this year.
Phase two is the larger slice of the pie which includes the erection of the new market hall itself as well as all the ancillary buildings around it.
The design of the second stage is still being finalised before being put out to tender, but work is scheduled to being immediately after Mr Wilkinson and his team complete phase one. Work began on the jetty’s construction in February, although Dean & Dyball guessed it had netted the deal before the final announcement in December 2007.
Planning the job
“I became involved when we became nominated contractor and we started the detailed design in September or October last year,” Mr Wilkinson says.
He adds: “It meant we could work out the buildability of the design during the build-up to the construction phase.”
With the site located at a pinch point between the sea and a rock headland overlooking the harbour and the narrow lanes around it, the team soon realised that the only logical way of building the new jetty would be from the seaward side using barges.
“There is very poor land access here and no storage. As we are using barges during construction we are also bringing material in by boat,” says Mr Wilkinson.
Effectively the design for the new section is of two 75m long, 12.5m wide jetties of infilled steel sheet pile walls.
These two jetties are linked together by a further steel sheet caisson at the seaward side and the section between them will also be filled and a slab produced using precise concrete beams placed over the top.
The sheet piles are being vibrated into position through 1.5-2.5 m of silt until they reach the limestone bedrock.
They are then driven up to 0.5 m into the bedrock using a 17.5 tonne impact hammer and tied across their width using 57.5 mm diameter Dywidag steel tie bars.
The outer seaward sides of the steel piles will be painted and protected from corrosion by a sacrificial anode system. Most of the fill being placed at the harbour is delivered by a boat which brings 1,300 tonnes of reclaimed aggregate from Cornwall’s china clay mines and recycled crushed concrete up the channel from Aggregate Industries’ Moorcroft Quarry, near Plymouth every 36 hours, weather depending.
China clay sand infill
The Dean & Dyball team decided to use the secondary aggregate – china clay sand – to fill the area between the steel sheet piled walls of the two jetties which make up the scheme’s design because of its structural strength.
It has also been well washed and barely discolours the harbour water when placed. The fact that it is cheaper than conventional aggregates because the aggregates levy is not payable on it has helped too.
“It is a sort of coarse quartz gravel. It has been washed several times during the cleaning up process and so there is minimal water discolouration when we place it.”
“Even that which does occur we are not sure if it is because of the material itself or the harbour silts being stirred up during the work. Structurally it works really well, it stands at a good angle, self compacts when put in water and it is cheap”, smiles Mr Wilkinson. “It’s great stuff.”
The fill being encased within the sheet pile walls themselves is also shipped from the Moorcroft Quarry near Plymouth.
Crushed concrete saved from the redevelopment of the Drake Circus shopping centre in the city will be encased between the steel sheet piles which will form the jetty walls.
Fortunately for Mr Wilkinson the design team ensured that the new structure is entirely independent of the existing fish market quay and so there are no awkward interfaces between new build and existing structures, although a 1.8m diameter stormwater outfall which exits between the two structures has had to be accommodated.
“There is a 50 mm gap between the new build and existing structure so we don’t have to worry about the interface between the two,” says Mr Wilkinson.
With work on track to hit the October completion deadline, despite a momentary hold-up thanks to new marine legislation (see below), all eyes are now shifting to the second phase of the fish market development – the market hall and ancillary buildings themselves.
Whatever the final design may be, it will have a solid foundation.
Seahorse alert
Dean & Dyball became one of the first contractors to carry out an investigation into the presence of two types seahorses at the Brixham fish market development.
Under changes to the Wildlife and Countryside Act which came into force in April, it is an offence to damage, obstruct or disturb the two types of seahorse found in UK waters, the short-snouted and the spiny seahorse.
The site team, working alongside client Torbay Council, called in an ecologist to check the presence of the fish.
Had they been found the contractor would have faced applying for a licence to work and possibly holding up the project.
Fortunately none were found, ensuring that work could continue unabated.
Making waves – cause for a rethink
Almost as soon as Dean & Dyball began work at the new Brixham fish market site it had to rethink its construction strategy.
The first structure to be built was a small retaining wall in the south-eastern corner of the site where the southern most new jetty doglegs from the junction between the existing fish market and the shoreline. Unfortunately the team had not taken account of the effect its construction would have on the swell size within the construction area. “Any bit of swell getting into the harbour was hitting the retaining wall and doubling the wave height.”
“We had created a bit of a problem for ourselves,” says project manager Simon Wilkinson.
To ensure building work could continue the project team realised the northernmost jetty would have to be built first to act as a breakwater to the rest of the scheme, enabling it to be built in the ‘shadow’ of the waves.