HARDING PRIZE COMPETITION 2024 | BTS


REFERENCES 1. United Nations Sustainable development goals: https://sdgs.un.org/goals


2. UK Net Zero Strategy: https://www.gov.uk/government/publications/net-zero-strategy 3. HPC project summary: https://www.edfenergy.com/energy/nuclear-new-build-projects/hinkley-point-c 4. HPC head placement summary: https://www.balfourbeatty.com/media-centre/latest/balfour-beatty-successfully-lowers-final-head-structure-into-position-at-hinkley-point-c/


5. BGS Lias group summary: https://www.bgs.ac.uk/geology-projects/engineering-geology-maps/engineering-geological-studies-of-bedrock-formations/lias-group


6. Underground Excavations in Rock, Hoek & Brown 2nd edition, 1982 7. Rock bolting in aggressive ground: https://link.springer.com/article/10.1007/s00603-021-02547-3 8. Amberg Profile summary: https://ambergtechnologies.com/solutions-services/amberg-tunnel/amberg-profile 9. Carranza-Torres C, Fairhurst C (2000) Application of the convergence-confinement method of tunnel design to rock masses that satisfy the Hoek-Brown failure criterion


10. HPC liner installation summary: https://www.balfourbeatty.com/media-centre/latest/balfour-beatty-installs-six-offshore-liners-at-hinkley-point-c/


11. EN 1992-1-1: Eurocode 2: Design of concrete structures. General rules and rules for buildings 12. CIRIA report C766 - Control of cracking caused by restrained deformation in concrete


QUESTIONS & ANSWERS: SUMMARY Following his presentation, David Maddison took questions from the BTS judging panel and the audience.


Questions began by seeking more insight into the waterproofing – techniques used, specification, and the required watertightness for the tunnels. In the discussion, specific to the tunnel to shaft connections (TSC), the operational need was noted as having limited requirements compared to other structures that have been designed having full waterproofing membranes. A challenge was noted, though, of placing waterstop bars and hydrophilic strips, especially at the sharp 90° elbow where there is significant rebar density. Discussing more achievability with the contractor rather than having Non Conformance Reports (NCRs) that need to be resolved.


At the time of the paper being presented, in March, the status of the activities was still in the temporary works (TW) stage, and leakage that is present is in terms of the intended pressure relief arrangements, draining the groundwater. The permanent works (PW) had yet to commence.


Further on pressure relief, it was explained that among the discussion points on site was the need to emphasise the design concept of pressure relief of groundwater in the bedrock, providing a dewatered zone for the TW stage of the tunnelling works. For that design strategy to be maintained in practice, discussions with the contractor focused on the importance of ensuring that the pressure relief holes (PRHs) were kept open, unblocked, uncovered, undamaged, and to continue to function.


It was added that waterproofing was worked well on the onshore tunnels, and where there was leakage along construction joints that gradually diminished, as the areas self- healed, to be in line with required limits.


Questions also considered trends in innovation, and David noted that when he first started work in a design office no one was particularly using 3D modelling. But much more use of those have been made, and it is especially helpful in the TSC layouts where the geometry is too complex for 2D design approaches – without incurring follow-on problems of adjustments, NCRs, etc, during construction. There is coming to be more alignment, in general, on the benefits of using such models.


In summary, the design has worked quite well so far, and lessons being transferred or embedded (such as updating TW drawings) and recognition of benefits of purposeful collaborative engagement across teams. Though, with the project still in the TW stage it can be noted that while benefits come in achieving continuity, in both strategy and information, this can be a challenge as it often relies on people and – as is common in the industry – they move around.


On early career progression, advice offered to others, and current university students, include: seek mentorship; grab opportunities where you can; dive in and immerse yourself in projects and site; and, there’s luck, while also knowing you have to fight for yourself a bit. In summary, engage – full-on.


Last, absolutely not least, and perhaps speaking on something for all, a recommendation: produce the ‘lessons learnt’ in tangible form; make them visible such that others can readily read and see, and understand, and use them, and spread the benefits. Make them demonstrably real, as a practice.


May 2024 | 21


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