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Soil nails bring stability to Gibralter

GIBRALTAR'S EAST Side Water Catchment structure is now stabilised and decommissioned after three years' work and installation of more than 8,000 soil nails.

Designer Gifford & Partners and geotechnical contractor Ritchies used roped access systems and specially designed drilling rigs to stabilise the steep sand slope beneath the 130,000m 2corrugated iron catchment structure. It was built in 1908 to collect rainwater.

Construction of a new desalination plant meant the structure, owned by the Ministry of Defence, was redundant and its iron sheets could be removed.

But analysis showed this could result in catastrophic slope failure.

Gifford's design was slightly amended by Ritchies to suit its working methods. These involved using rigs working on the iron sheets to install the 13m long Dywidag soil nails, grouted over a fixed length of 6m in the sands.

Soil nailing was finished early this year, allowing removal of the iron sheets and parts of their supporting wooden framework.

Some framework was retained to attach coir geotextile which will be used to establish vegetation on the slope for longterm stability.

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