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Cleaner by the Tay

GEOTECHNICAL CONTRACTOR Ritchies is halfway through a major ground anchoring contract for a new wastewater project on the east coast of Scotland.

The Tay Wastewater scheme is being built by the Bechtel Morrison EPC joint venture (Bechtel Water and Morrison Construction). About 14.5km of 1,200mm diameter pipeline is being laid from Arbroath to Dundee along the shoreline of the Firth of Tay.

It will intercept 41 foul outflows that discharge into the river, thus protecting the environmentally sensitive waters and shoreline of the Firth. Six pumping stations are being built along the route, together with a new wastewater and sludge treatment plant.

Ritchies, the geotechnical division of Edmund Nuttall, was awarded the £0.45M subcontract to design and install more than 230 highly loaded ground anchors. Working loads vary from 750kN to 1,950kN.Anchors were designed to suit ground conditions at the pumping station shafts.

Between 20 and 59 Dywidag Systems International double corrosion protected strand anchors have been used at each site, with a total capacity of 285,000kN.

The 200mm diameter, 20m deep boreholes for the anchors were drilled using down-the-hole hammers on Atlas Copco crawler hydraulic top-drive rotary drill rigs.

Between two and eight anchors were installed per rig shift, the amount depending on anchor capacity, access and geology. Before the main work began, test anchors were installed to verify design. All were successfully loaded up to three times the working load.

Ritchies is now over halfway through its 26-week contract and has been awarded additional minipiling and grouting work.

The public-private partnership project, due to finish at Easter, involves North of Scotland Wastewater Authority paying tariff charges to Catchment, the private consortium made up of Bechtel Water Technology, Morrison Construction and United Utilities.

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