Dug "by hand": https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ https://hornseyhistorical.org.uk/piccadilly-line-extension-p... https://en.w

Dug "by hand": https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ https://hornseyhistorical.org.uk/piccadilly-line-extension-p... https://en.wikipedia.org/wiki/Tunnelling_shield#Manual_shield_tunnelling https://en.wikipedia.org/wiki/Tunnelling_shield#Manual_shiel...