The Albert Street City Rail Link (CRL) trench has reached its full 18m depth near Wyndham Street.
A 100-year-old stormwater pipe at the base of the trench is now being removed, to allow the construction of the CRL tunnel box at the southern end.
A redundant stormwater pipe will also be unearthed as the excavation moves north.
At the Customs Street intersection, the pipe is at a depth of only eight metres. The old pipe and a pumping chamber must be removed as they are in the way of the future CRL rail tunnels.
The current depth of the remainder of the trench is between 3.5m and 6m.
On the Commercial Bay development site between Lower Queen Street and Albert Street, the first complete section of CRL tunnel has also been finished.
This is the first quarter of a total 100m of rail tunnel that will be built through Commercial Bay by April next year.
It will join the tunnels coming down Albert Street and those coming from Britomart Station.
