Because the tunnel is going underneath the Sydney harbour: https://www.smh.com.au/national/nsw/under-wraps-sydney-s-first-rail-tunnel-dug-beneath-harbour-20191

Because the tunnel is going underneath the Sydney harbour: https://www.smh.com.au/national/nsw/under-wraps-sydney-s-first-rail-tunnel-dug-beneath-harbour-20191121-p53cs3.html https://www.smh.com.au/national/nsw/under-wraps-sydney-s-fir...