Barrett Byrd Associates

Breaking rock is not as hard as breaking into the UK rock armour market but RMC Aggregates has managed to get a foot in the door with recent repairs to Ramsgate’s breakwater. Claire Symes reports.

Most rock used on coastal protection schemes in the UK comes from France or Denmark mainly because these candidates can supply large volumes with a good reputation for toughness. Similarly durable rock exists in this country but quarries here are seldom well located for shipping the material to where it is needed.

RMC Aggregates’ Dean Quarry in Cornwall has more potential than many of its UK counterparts – it has a coastal location with a jetty and the gabbro rock quarried there is particularly hard wearing. The quarry’s merits helped RMC beat off European competition to win its first rock armour supply contract for recent repairs to a breakwater at Ramsgate in Kent.

“UK quarries often lose out on rock armour contracts because there is a general lack of confidence in both rock quality and the ability to deliver,” says RMC Aggregates South West marine sales manager Wayne Towell. “From Dean we can supply fairly large quantities of high grade rock but loading from our quay, like almost every other UK quarry, is very weather dependent. But by picking rock armour contracts which need material supplied between spring and autumn we can be fairly confident that the weather conditions will be on our side.”

RMC is supplying rock to coastal engineering contractor Marine Civils, which won the contract to carry out routine maintenance on the breakwater from Thanet District Council’s (TDC) main contractor Van Oord earlier this year. TDC and Van Oord’s engineers jointly carried out the design for the work but left sourcing of suitable stone to Marine Civils.

“The scheme at Ramsgate is fairly small in coastal defence terms but still needed 1000t of high strength rock which could resist attrition by the waves for the design life of the scheme,” says Marine Civils chairman Rob Radmore. “Rock from Denmark or France is usually the automatic choice for such schemes but the overheads for shipping this quantity of material made European sources financially less viable, so we started looking closer to home.”

Marine Civils search included a visit to RMC’s Dean Quarry near the Cornish village of St Keverne where the company initially carried out a visual inspection of the rock involving discontinuity surveys. Marine Civils was impressed with what it saw and commissioned physical testing to ensure the gabbro was up to the job. RMC supplied Marine Civils with all the necessary technical data and the rock passed the testing process with flying colours.

“Gabbro is formed by igneous intrusion into the existing geology and its crystalline texture and chemical make up helps create stone which is not only very strong but is also very dense,” says Towell. “Rock for coastal defence schemes is usually specified by weight, so the denser and hence heavier, the rock, the less of it is needed to complete a scheme. In effect dense rock like gabbro makes coastal defence schemes more environmentally friendly because a smaller volume needs to be quarried for each project.”

RMC supplied the 1000t of rock in 3t blocks which were loaded onto Marine Civil’s barge Longrock using its onboard 95t crane. “The high density of the gabbro kept the volume of the rock down, so we were able to transport all the rock needed in one go,” says Radmore. “Loading of the rock was always our biggest concern about using Cornish stone but the careful planned operation went without a hitch.”

Once on site in Ramsgate the rock was placed piece by piece onto the breakwater, again using Longrock’s onboard crane, to ensure that each block keyed into its neighbour. According to Radmore, placing of the stone is almost as critical as the type of stone: “If the rock is not placed in the right position the breakwater would be like a brick wall without the mortar,” he says. “Each rock holds another in place enabling the individual blocks to act as one structure and resist the impact of the waves.”

Dean Quarry’s first supply of rock armour is now safely in place and it looks as if the success of the contract is helping to change the perception of UK quarries’ abilities in terms of costal defence. Towell says that he is already involved in discussions to supply 60,000t of gabbro from Dean for another coastal protection project but is remaining tight lipped about the details.
Marine Civils is also now convinced: “We would definitely look to use rock from Dean Quarry on any future schemes we are involved in,” says Radmore. “We would always prefer to use rock sourced in the UK than take business overseas.”

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