According to government figures, the UK cannot rely on fossil fuels for its long-term energy needs: a combination of soaring oil and gas prices, dwindling fossil fuels and public pressure to tackle climate change means increased support for nuclear power. The Hinkley Point C nuclear power station in Somerset has the potential to contribute 13% of UK energy needs, which means burning fewer fossil fuels and reducing the volume of harmful carbon dioxide in our environment. Developer EDF Energy is constructing the power station.
The energy giant needed to compile specific ground investigations and hired award-winning Structural Soils, an RSK company, to act as its environmental and engineering specialists. Structural Soils investigated the integrity, structure and geotechnical nature of the ground earmarked for two reactors and associated structures. The data from the investigations would inform EDF’s planning submission and the structural designs of the station. The remit was varied: The Structural Soils team expected challenges, but the company is a recognised industry leader for solving challenges with professionalism and ingenuity.
A three-front investigation: Drilling, surveying and testing
Structural Soils engineers drilled 4000-m boreholes, some reaching depths of 140 m, and dug 140 geotechnical and environmental trial pits. For engineers to study anomalies, identified by a geophysical survey, some of the rotary boreholes were drilled at 30 and 45° angles. Radioactive contamination was a possibility, so engineers installed a second tier of 20-m-deep aquifer protection measures on certain areas of the site. EDF’s stringent environment plan meant that no drilling flush could seep into the ground; with no fresh water on-site, Structural Soils was left with a logistical challenge. Engineers estimated that they needed between 1000 and 2000 litres of water to carry out just 1 m of core drilling. Their solution was to create a large network of surface water supply pipes across the site that were charged by water pumped under considerable pressure from 30,000-litre tankers. An army of 1800 intermediate bulk containers collected the used water and transported it off-site for disposal.
The project’s scale and complex geology meant that the team needed to undertake a considerable array of testing and surveying, including
- surface seismic refraction and resistivity tomography surveys
- cross-hole, up-hole and down-hole seismic testing
- down-hole optical televiewer logging and geologging to identify the in-situ physical properties of the geology
- in situ testing including static cone penetrometer tests
- hydraulic fracture testing
- Menard pressuremeter tests
- high-pressure rock dilatometer tests
- packer permeability testing, which formed a large part of the investigation
- large-scale pumping tests.
An experienced group team of more than 10 engineers collaborated with specialists from throughout Europe to accurately carry out several testing methods rarely used in UK site investigations. The team’s UKAS-accredited lab completed extensive core testing and logged geotechnical borehole data to characterise the properties of the different lithological units. The data informed EDF’s successful planning application. The nuclear power station has evolved from the planning stage and is now under construction.