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Moray East Offshore Windfarm

Moray East Offshore Windfarm

 

The Moray East Windfarm will produce some 50 MW of electricity through the use of offshore wind turbines that have a maximum blade-tip height of 204m and which are positioned a minimum distance from the shore of 22km.  To get the electricity into the National Grid, at a new sub-station to be constructed at New Deer, Aberdeenshire, there will be 86km of cables installed, 52km of which will be offshore.

The shore landing position for the cables is between Banff and Whitehills on the Aberdeenshire Moray Firth Coast.  At this location there will be three cables that terminate in junction boxes, all below ground.  A 1016mm diameter steel casing was to be installed, at an angle of around 15to the horizontal, using a down-the hole drill.

The complication at Moray East was that running parallel to the shore line and before bedrock was reached there was a 225mm diameter HDPE sewer pipe, part of the local sewerage system owned and operated by Catchment Moray.  They were concerned that levels of vibration from the hammering associated with the drilling to install the steel casing, that would pass some 2m below the sewer, would give rise to unacceptable levels of vibration.  

As a way of addressing the concerns of Catchment Moray, LMR engaged Vibrock Limited to undertake a vibration assessment of the likely levels of vibration that would be generated on the sewer and to recommend safe levels of vibration for this important infrastructure service.  Having recommended a criterion the Vibrock data base of vibration measurements was interrogated for results of comparable activity that had taken place in similar ground conditions.  From this analysis of the available data the "most likely" and "maximum" peak particle velocities on the sewer were predicted.

Vibrock was also engaged to supply instrumentation, a Vibrock V9000 digital seismograph, and to install the transducer directly onto the sewer.  They also undertook some of the initial monitoring during the installation of the central casing.  The highest vibration level recorded was in line with the most likely vibration level predicted for the project.

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