AS THE night shift sleep by day, nearby another crew prepares the deck units at a casting yard set up to supply the job.
Two parallel lines of work are set up - one with shutters in preparation for the next pour, the other with the curing slabs awaiting application of waterproofing and surfacing. Slabs along a line are poured alternatively, with the infill slabs revisited to allow for hydration and relaxation of the shutters.
Units vary between 375 and 400 mm in thickness. These replace the existing 225 mm-thick deck, with 100 mm road base course surfacing applied with conventional surfacing equipment. Slabs are applied with bondbreaker at the interfaces and are waterproofed prior to surfacing.
The surfacing material is cut so each deck unit separates before being placed.
Tents ensure progress in all weathers. A specialist system designed by Dr John Broomfield of BGB Projects is also cast into slabs, enabling remote monitoring of corrosion rates of reinforcement over the 120-year design life.
About 30 men work in the yard.
'Some of us have been together for four years since beginning work on the East Tunnel, ' says yard foreman Eric Milne.
Like their nocturnal counterparts, the team has built up speed since the start of the job and now turns out 12 units a week, with a total turnaround from start to finish per unit of nine days.
'It's a very busy shift and we are around 60 units ahead of the tunnel work, keeping us five weeks ahead of the tunnel, ' says precast section engineer Julian Mee.