The arch and the arch of the tunnel
This part of the tunnel lining is generally the first pouring, pouring formwork trolley can be placed on the inverted arch concrete and support, to the construction of the tunnel arch wall concrete.
Tunnel invert refers to the bottom of the tunnel (anti arch, so called inverted arch)
Tunnel arch wall refers to both sides of the tunnel wall and the top of the arch, the tunnel arch wall is generally the use of a template trolley.
