AdvertisementNationalNSWSydney Metro What happens to our metro tunnel boring machines when they hit the end of the line? These mechanical behemoths were Betty and Dorothy, the tunnel boring machines tasked with digging the Sydney Metro West tunnels. “The steel has exceeded its wear limits,” a metro spokesperson said. A construction worker walks near the tunnel boring machine named Dorothy. Sydney Metro Jessie and Ruby are mixed shield (slurry) machines, designed for the challenging conditions under Sydney Harbour and the CBD.