Though still very much in its infancy, tidal energy is gaining momentum. In 2006, the first test rig turbine was installed and generated electricity to the UK grid using OpenHydro prototype. Seven years on, the Meygen project in the Pentland Firth is planned to be the UK’s first commercial tidal project, initially comprising six turbines with a total installed power of 9MW with planned further expansion to 86MW. 

Unlike offshore wind, which has seen huge investment from major energy companies, smaller developers and intelligence investors have been the key players in this emerging market. Despite limited capital, a number of Tidal Energy Converter (TEC) devices have now been installed at several locations around the UK.

The primary design challenges inherent in high tidal energy environments include geotechnical uncertainties. For one, the bedrock geology of the UK coastline is complex and varies significantly across the country. From Precambrian age well indurated marine sedimentary rocks such as sandstone, limestone and shale in the West of Scotland, and indurated slates and schists around the Welsh coastline, a variety of basement type materials need to be considered for foundation design. In addition to this basement geology, a thin veneer of unconsolidated coarse sediments often blankets these materials.

Site investigation of tidal turbine environments can be extremely difficult and challenging; hence geotechnical design and installation elements pose a major risk to the project unless properly considered and effectively managed. Jagged hard substrates often present challenging seabed profiles (see rendering) to design around and where typical seabed preparation techniques, such as rock carpeting or dredging, may not be practical or feasible.

Data acquisition

In order to promote efficient design and realise cost savings, a comprehensive site investigation program should be developed. Ideally, this should begin with a detailed desktop study, shore site walk-over and geophysical and visual camera survey for initial investigations before moving to more complex and costly geotechnical surveys comprising potentially onshore, nearshore and offshore drilling.

A detailed geophysical survey combining surface and subsurface techniques, such as multibeam echo sounder, side scan sonar and sub-bottom profiler, are essential to understand the topography of the development area to select and optimise not only the location of the TECs, but also the lay routes of inter-array and export cables. The aim of such surveys is to identify hazards whereby potential mitigation measures may need to be developed. 

Geotechnical data to deeper depths (~20m to ~30m below seabed) may be required to perform a detailed foundation design to address such issues as foundation capacity, soil-structure interaction and install ability.

Whilst offshore geotechnical drilling can seem expensive, the data can potentially be further supplemented by data from an onshore drilling campaign which will allow for further laboratory tests to be carried out in an attempt to better understand the variation in the properties of the bedrock and their geotechnical characteristics at a fraction of the cost of any marine investigation.

Additionally, material specific research on soil-material interface friction may also to promote efficient foundation designs. Acquisition of appropriate data to coincide with appropriate project milestones will culminate in a comprehensive understanding of the geological features and geotechnical conditions relevant to design.