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Rosyth completes record rock anchor tests

TESTING ON what is believed to be the biggest rock anchor contract in the UK has been completed. The contract for the rock anchor installation and dock refurbishment of the entrance lock at Rosyth Royal Dockyard in Scotland was won by Kvrner Group Partnership, a joint venture of Kvrner Construction and Kvrner Cementation Foundations.

The work is being carried out to increase the seismic loading capability of the lock, which is used as a dry dock for the Royal Navy's nuclear submarines. The preferred option was to pin the existing mass concrete walls to the bedrock below and behind the walls, to increase the mass of the wall. This would prevent any seismic activity from causing sliding or overturning. Schal Project Management and its design team TPS Consult and NNC carried out the design and analysis of the scheme.

Approximately 30% of the £4.5M ($7.2M) project cost was for manufacture of the rock anchors and bearing plates. Kvrner Cementation Foundations opted to set up a dedicated fabrication facility at its Doncaster plant to reduce costs and improve management.

All the anchors, with full double corrosion protection, were manufactured there in conjunction with Dywidag Systems International providing the supervision, material and specialist equipment.

On site works included drilling, installing and stressing 1200 rock anchors, which varied from 16.5m to 30.5m long. Six hundred anchor recesses also had to be cored in the dock walls. Eight C6 drill rigs owned by the contractor were used to carry out the work from access platforms, using down the hole hammer drilling, at up to five locations at any one time.

Large diameter core barrels, up to 800mm, were used to form the 1.6m deep recesses for the anchors, as opposed to conventional small diameter stitch drilling. As a result, circular anchor plates had to be used instead of square.

Reconstruction of the service subway roof was also included in the contract - the initial plan was to carry demolition out before the drilling. But in the end the two operations were reversed to facilitate access for the craneage which was needed for moving the access systems in the dock. Anchor boreholes could be drilled up to four weeks before anchor installation with no reduction in the performance of the anchors.

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