TECHNICAL | SHAFTS, CAVERNS
Q&A Following their presentation, Joe Hardwick, David Maddison and Barry Gilsenan took questions from the floor and
online. The Q&A has been edited for available space.
Q: For the interface of Permanent Works and Temporary Works, how were responsibilities divided, such as Jacobs’ role and Balfour Beatty’s? A - Joe Hardwick (JH): It was managed under BS 5975. We decided who was most appropriate to design each element. For various stages and lot of the offshore interface with SCL, which interfaced heavily with the Permanent Works, we decided the Temporary Works would best sit, from a design perspective, by the Jacobs/Amentum/CH2M team, depending on the name of the business or section at the time. Other items, such as the IRP, had major interfaces with the tunnel loads during breakout and were designed by specialists such as Herrenknecht. Process is very much managed by Balfour Beatty. Case by case, we worked out who was best placed to do it and understood the interface and who was responsible. A - David Maddison (DM): There are many people to convince — consultants, the contractor, their designer, the Category 3 checker, the safety process and other bodies. With any innovation, it is not just about convincing ourselves. That is one of the biggest benefits of having had an innovation process running for so long. The rock bolting Temporary Works had to directly input to the Permanent Works design, so it had to be one system. Otherwise, we could not have done the permanent nuclear design or understand how temporary loads impacted upon the Permanent Works. Even though we could not consider the SCL as supporting the Permanent Works it still directly affected them. It was a reason we used so many different software packages to try to find the correct answer. A - Barry Gilsenan (BG): Early Contractor Involvement (ECI) started in 2011. It evolved through various stages. When Balfour Beatty came on, in 2017, the project moved into Detailed Design. Then decisions made on interfacing between Temporary Works and Permanent Works. For onshore tunnels it was a different Temporary Works and SCL, and the Permanent Works by another team. For the offshore works, the interface and complexities meant it was best managed by one team as a system – which had big advantages. The NEC Contract options also helped, starting on Option C and moving to Option E, which due to the complexity supported the collaborative approach. The approach worked really well.
Q: How was project insurance organised? Did each party carry its own insurance? A - JH: It was a mix. The contractor had insurance up to certain limits, designers had limits, and above certain limits it was the wider programme insurance, held by NNB.
Q: How did you address stakeholder management to create the ‘golden thread’ through the project needed to deliver the solution? A - DM: A lot of it came from the design team being embedded with the contractor, engaging with them throughout the process. I would recommend getting designers out on site. A - JH: From a wider stakeholder perspective, and while some projects have more direct interfaces with the public and other
organisations, here we were not involved with such.
Q: Did any upward vertical displacement occur due to uplift after the dewatering process? A - JH: We had people on both sides: would it move up or down? Ultimately it moved down, by an incredibly small amount. (The red trigger level was about 3mm). Much of the discussion was almost about monitoring accuracy.
Q: On risk mitigation, were there hold points during excavation, awaiting feedback on geotechnical face mapping or other information? A - BG: There were many gates to get through before the start and during construction the process was managed through the Daily Review Meetings (DRM) and Permit-to-Work system. A - JH: The DRM process helped get information quickly and assessment systems followed. An Expert Panel contributed, as necessary, which comprised Prof Robert Mair and industry experts. A - DM: With six very similar structures, lessons captured benefited the next.
Q: Can much of the design be used on Sizewell C? A - JH/DM: The ground conditions are very different. The current concept for Sizewell is also for online connections, so the design approach is different. Lessons are being passed on, and formal arrangements are being developed to allow that knowledge sharing. People have also moved across. Some of the most useful transferable lessons are more about working on a nuclear power station project. A - BG: In the early phases at Hinkley, the online/offline connection option was very interesting. What would come first - tunnels or shafts? We discussed many options before settling on the offline, cross passage-style solution.
Q: Were technical requirements written and fixed at the outset? A - DM: There were many specifications and guidance requirements from NNB and EDF. Those not from Jacobs or Balfour Beatty were project requirements for the design to meet. A - JH: Balfour Beatty had its own assurance team. The client inspected for construction compliance. There was a strict design specification from the outset. The responsible designer effectively owns that design specification as part of the Nuclear Assurance Process. Any change has to go back through that route.
Q: Were there specific requirements for the grout at the segments, and testing? A - JH: The grout was similar to other major projects, but here every material has a Material Acceptance Report, or MAR. An off-the-shelf product is usually quicker while a mixed or new product, such as a concrete mix, can take months or years to approve, from constituents to testing – which continues during use.
24 | September 2026
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