Land and water based geotechnical invesigation at Shapinsay

Tuesday 06 September 2011

The Client

Scottish Water has around 5 million customers in 2.4 million households. Because Scotland has over 6,800 coastline and a small and relatively dispersed population, it requires a large number of small water and waste water treatment works.

Scottish Water Solutions Limited (Solutions) was formed in 2003 by Scottish Water to manage and deliver the majority of its Quality & Standards II Capital Investment Programme, to improve Scotland's water quality and wastewater treatment processes. Solutions is operated by seconded staff from Scottish Water and each of the partner companies, one of which is Jacobs, the world's largest and most diverse providers of professional technical services.

Shapinsay

Shapinsay is one of the Orkney Islands, situated off the north coast of mainland Scotland and a 25 minute ferry ride from Orkney's capital, Kirkwall.

The 300 residents currently drink treated water that is supplied from boreholes on the island. However, this presents some challenges. Firstly, the supply is limited, so during dry periods such as the summer, extra water has to be tanked across to the island. Secondly, were the population to grow significantly, it could mean that too great a deman would be put on the existing supply.

As the island's water utility provider, Scottish Water Solutions is looking to improve the reliabilty and the quality of the water supply to Shapinsay.

Jacobs contracted ESG Soil Mechanics to conduct the geotechnical investigations for providing a 5km pipeline between Shapinsay and Orkney (2km of which, would be under the sea bed). The results would then be used to assist in determining the pipeline's viability and construction options.

The site investigation

The pipeline is planned to run from the treatment works in Orkney to Shapinsay, following the existing road layout and running on the seabed in between. The site investigation work took place in June 2011, over a three week period, including the heavy plant mobilisation.

The land-based investigations used a lorry-mounted rotary rig to gather geotechnical data up to 60m below ground. Boreholes were drilled at the planned entry and exit points for the pipeline under the sea.

The water-based investigations included a marine seismic reflection survey across "The String" (the Shapinsay Sound, which is located between the Orkney Mainland and the Island of Shapinsay) to confirm firstly, the thickness of marine sediments and secondly, that no major geological structures existed in the depth range of interest. Seismic profiling techniques using "boomer" and "sparker" were deployed to identify the sub-bottom geological strata along the proposed route to a depth of about 65 metres. In addition to the seismic data, geophysical surveys using single beam bathymetry and side scan sonar collected data along the survey lines, to assist with the characterisation of the sea bed.  

Local wildlife considerations

A small island off Shapinsay is home to a local common seal colony and the proposed pipeline is due to pass close by.

Commissioned by Scottish Water Solutions, a Marine Mammal Observer was stationed aboard the vessel during the survey operations, as the site was situated close to a haul out point for the seals. In order to create as little disturbance as possible to any seals or cetaceans that may have been in the vicinity, the equipment was run up using "soft starts" prior to the collection of survey data.

Customer Support

ESG Soil Mechanics has supported Jacobs and Scottish Water Solutions with investigation work on the mainland for several years.

Malcolm Miller, Construction Manager at Scottish Water Solutions Limited says "this is an exciting project and one which will make a real difference to the Shapinsay residents. The site investigation played a critical part in determining the pipeline's final designs and ESG were selected, based on their value and expertise."

The site investigation is now complete and the pipeline is in the next stage of development.

 

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