The final pre-cast concrete segment has been built for the Sydney Metro railway tunnels.
Manufacturers in a factory next to the rail-line in Marrickville, the concrete walls of the railway tunnels have been delivered to tunnel portals beginning in Chatswood and extending under North Sydney, via Barangaroo and the CBD, on to Waterloo and then exiting in Sydenham.
The final part is one of 100,000 pieces of concrete that will secure the twin metro tunnels.
Each tunnel ring is made up of six segments, and a seventh segment, known as a keystone, is added for the under-harbour section of the tunnels.
The purpose-built factory produced one four-tonne segment every six minutes and employed 140 people.
The tunnels run for 15.5km and were carved out of the stone beneath Sydney by five tunnel boring machines.
39,600 segments were trucked over the Sydney Harbour bridge to be installed north of the harbour.
In total, 358,920 tonnes of concrete were used.
In December 2019 the first tunnel underneath Sydney harbour was completed, and four tunnel borers were removed in February 2020, with tunnel boring machine Kathleen completed the final railway tunnel under Sydney harbour. Completion of the metro line to Bankstown is expected in 2024.