Tunnelling for Australia’s biggest public transport project is about 50 per cent complete after another mega boring machine broke through into the new Crows Nest Station site.

Only four weeks after Tunnel Boring Machine (TBM) Wendy arrived, TBM Mabel’s cutterhead broke through a wall of rock at the new Crows Nest Station site after tunnelling about three kilometres from Chatswood.

Mabel will spend a few weeks undergoing maintenance before being re-launched at Crows Nest and tunnelling towards the next future Sydney Metro station at North Sydney.

TBM Mabel and TBM Wendy are building 6.2 kilometres of tunnel which will link the recently opened North West Metro at Chatswood to the harbour’s edge at Blues Point.

The borer is named after Mabel Newill, a matron at Royal Prince Alfred Hospital (RPAH), who introduced sanitisation techniques to help stop the spread of typhoid in Sydney in the early 1900s.