Are you describing "Cut and Cover" ?
As in "Cut and Cover is a method of construction of shallow tunnels"
https://en.wikipedia.org/wiki/Tunnel_construction#Cut-and-co...
It has been used for centuries, e.g. was used to dig the first parts of the London underground in the late 1800s
Are you describing "Cut and Cover" ?
As in "Cut and Cover is a method of construction of shallow tunnels"
https://en.wikipedia.org/wiki/Tunnel_construction#Cut-and-co...
It has been used for centuries, e.g. was used to dig the first parts of the London underground in the late 1800s