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The three firms have come together to form the GSA which sits within the wider Civil Works Alliance (CWA), which includes Sizewell C, Balfour Beatty, Laing O’Rourke, and Bouygues Travaux.

The alliance is responsible for delivering the project’s main civil engineering works.

In an announcement on 17 July, Sizewell C said the GSA “is thought to be the first geotechnical sub-alliance of its kind in the UK” and will “deliver a range of specialist ground engineering solutions – including piling, soil mixing, diaphragm walls and plastic cut-off walls”.

The GSA was “created to maximise operational safety, capability, quality, and delivery”, and it “will create a stable and watertight platform capable of supporting the immense loads associated with the construction of the new nuclear power station”, Sizewell C said.

GSA alliance manager Vincent Leblois said: “We bring together a wealth of global capability, sector expertise and experience to the Sizewell C project.

“We are working very much as one team delivering one outcome on a ‘best for project’ basis through joint decision-making, strong delivery and using the best people for the job.

“Together and as part of the CWA at Sizewell C, we are creating the foundations to power our future, excited to be contributing to the build and completion of this vital investment in new infrastructure for Britain.”

Balfour Beatty Ground Engineering managing director Jane Towse-Laval said: “Sizewell C represents one of the most significant infrastructure projects in the UK, and we are proud to bring our specialist geotechnical expertise to this pioneering sub-alliance.

“By working collaboratively, we will combine innovation, technical excellence and our collective expertise, laying the essential foundations for the safe and efficient delivery of this nationally significant energy asset.”

Sizewell C CEO Nigel Cann said: “This unique alliance reflects what our project is all about – true partnerships bringing together world-leading expertise, delivering big gains in innovation and productivity.”

Separately, Sizewell C’s latest annual report has provided further insight into the project. Published on 6 July, it is titled Sizewell C: Annual Report & Accounts FY25/26.

On 15 July, Department for Energy Security and Net Zero (DESNZ) minister of state Michael Shanks issued a written statement about Sizewell C.

“The [report] provides a comprehensive account of the company’s activities during 2025-26, recording a year of major milestones for the project, including the expansion of construction activity on site, growth in the workforce, and continued development of the project’s delivery arrangements.

“It also provides updates on the project’s strategic priorities looking ahead, project finances, governance arrangements, and its approach to managing delivery risks and opportunities.”

The also report includes a diagram showing “key milestones in the Sizewell C power station life”, which says the project is currently between “financial Close and Revenue Commencement – Regulated Asset Base (RAB) model and financing arrangements in place”, which happened in November 2025, and in future “main earthworks” which includes site preparation, excavation and groundworks, scheduled to take approximately three years.

The report does not specify when the main earthworks will begin.

After reviewing the report, a Stop Sizewell C spokesperson told NCE: “Sizewell C’s Annual Report broadly complies with Ministers’ obdurate refusal to give any useful information about how long Sizewell C will take to build, which, considering that taxpayers and householders are stumping up vast quantities of cash, is unjustifiable and disrespectful to struggling local communities.

“The only reveal is that “J-zero” is expected sometime in 2029. Given the complex site de-watering, cut-off wall construction and platform raising, it is little wonder that it will be at least five years since works formally began, in January 2024, before Sizewell C can even begin above-ground construction.

“We maintain that the chances of Sizewell C being delivered on schedule are slim to none, and the new prime minister and energy secretary would be better off cancelling it now.”

University of Greenwich emeritus professor of energy policy and Energy Policy editor-in-chief Steve Thomas told NCE that the construction timeline in the report shows “how hollow all the Fingleton nonsense was, that it takes five  years of site prep to get to construction start. Not because of regulation or planning.”

The Nuclear Regulatory Taskforce published the Nuclear Regulatory Review 2025 in November 2025, which was also called the Fingleton Review. It found that regulations including the planning system were to blame for the delays and cost overruns faced by nuclear projects.

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