ABSTRACT
The Hinkley Point C nuclear power station cooling system offshore connections require the break out from a segmentally lined tunnel, mining up to the side of a pre-installed temporary steel liner, break into and sequential removal of the base of the liner to create sufficient room to construct the permanent works. Tunnelling through weak-to-very weak horizontally bedded mudstone with high ground water; permanent works constraints requiring difficult geometry and large openings in the segmental tunnel all mean that the offshore connections are relatively short but incredibly challenging tunnels with complex geometry, multiple interacting structures, relatively low cover, challenging ground and ground water conditions (2nd highest tidal range in the world) … And all to be repeated 6 times! From segmental tunnel support systems; multiple rounds of ground investigations; ground treatment; pressure relief systems; temporary steel liner and ground support design; innovative risk review process; expert review panels, this paper describes the challenges posed and presents the design/construction mitigations implemented in order to ensure the safe construction of these first-of-a-kind structures.
