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Taking steps

A combination of ParaLink reinforcing strips, Terramesh units and traditional steel mesh gabion faces was used to great effect recently for a new 15m stepped front quay wall. The wall was built as part of the refurbishment of the Nigg drydock in the Cromarty Firth in Scotland.

Terramesh units measuring 6m by 2m by 1m were installed in rows at the site in April 1997, lined up along the 240m base of the soon to be constructed stepped front face. The Terramesh units, manufactured and supplied by Maccaferri, were hand packed with stone to ensure a high standard of finish by contractor Morrison Construction.

Each Terramesh unit had a reinforcing tail which was unfolded to a length of 5m, before soil was backfilled on top to a height of 0.5m. Layers of ParaLink 300M were then unrolled onto a bed of compacted sand from rolls of 6m width for the first third of the wall, up to a length of 20m in from the Terramesh units. An additional backfill of 0.5m of soil was compacted before the surface was levelled for the next layer of gabion boxes to be placed, this time 1m stepped back from the first.

'We needed a hard-faced finish rather than a soft face, so steel mesh gabions were selected for the exposed face of each layer. The addition of ParaLink provided the high tensile strength which was required for the integrity of the quay wall,' said Maccaferri marketing manager Colin Evans.

According to Evans, the large core stones for the Terramesh units were placed by hand to achieve the maximum possible density of stone fill, preventing excessive settlement. ParaLink's low creep polyester fibre design and tough polyethylene casing helped mark it out as the ideal material for the harsh climate of Nigg.

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