SCARBOROUGH BOROUGH Council this week confirmed that 15 of the 4,040 concrete Accropode sea defence units lining the town's 1.4km headland had broken up.
The units that have failed are at the toe of the revetment. Engineers are now concerned about implications for the rest of the sea defences (see box).
Investigators were this week thought to be examining concrete quality and installation methods as possible contributing factors to the failures.
Sea defence experts told NCE that concrete quality could have been a factor because the precast, unreinforced Accropodes had failed within a few months of installation.
They said this was more likely as the proprietary Accropode design had been widely used without problems. The units could also have failed if placed too roughly, they added.
French hydraulic engineering firm Sogreah holds the Accropode patent and licenses production to contractors rather than manufacturing them itself.
At Scarborough, the massive 9m 3, C25/30, concrete structures were manufactured and placed by contractor Edmund Nuttall under a £33M contract with Scarborough Borough Council.
Designer for the £33M sea defence project is High Point Rendel with HR Wallingford providing additional consultancy services.
Some of the Accropodes have split down the centre and others have suffered fractures of their interlocking limbs, causing them to shear off.
So far 15 damaged units have been discovered. But engineers from the council, High Point, Nuttall, HR Wallingford and Sogreah were still surveying the units lining the 1.4km headland in situ as NCE went to press.
Details of the problem were presented to Scarborough Borough Council members last week in a report by chief executive John Trebble and head of engineering and procurement, John Riby.
'Initial inspections and conclusions by the engineers and Sogreah have indicated that the present situation is not sustainable and these units will need to be replaced, ' says the report.
'A costed action plan will be produced and reported to the cabinet, ' it says. This is expected within the next few weeks.
Sogreah project director Michel Fons told NCE that there was no obvious reason why the Accropodes were breaking up at Scarborough.
He said that Sogreah had licensed its product to more than 140 projects and had only had problems when the Accropodes were being placed on soft material requiring foundations.
'We have had problems on previous works when the engineer was not careful enough when designing the foundations, ' he said.
At Scarborough the Accropodes do not need foundations as they sit on rock. They are secured at the toe by 775mm diameter precast concrete piles.
Engineers close to the project have dismissed the possibility that severe weather damaged the Accropodes.
'We haven't had much more than a 1 in 1 year storm event in Scarborough over the past year and the defences are designed to withstand a 1 in 100 year storm, ' said one .
'It is also significant that the Accropodes that have been damaged are near the toe of the structure, as the nature of the tide is such at Scarborough that you can't get big waves at the toe, which suggests that this is not a water problem, ' he said.
Nuttall and High Point would not comment on the failures until they had completed their investigation.