Tunnel portal

What a tunnel portal is

A tunnel portal is the built face at the mouth of a tunnel. It closes the end of the lining and, being the only elevation visible from outside, it is where the design effort goes.

Records list its parts. The former Hokuriku Line Ashidani tunnel in Fukui Prefecture, built in 1894, is described as lined in brick throughout including its Refuge recess, while its portal, like others built by the same contractor, carries pilasters, a Coping stone and a string course, the whole built up in dressed stone.

The Habara tunnel on the same line, built in 1896, is described as having a near-symmetrical portal of dressed stone with pilasters and a parapet thrown out at length to either side. The Yuno tunnel, from about 1895, has a north portal with a long parapet and four pilasters.

Lining and portal often differ in material. Ashidani is brick inside and stone at the face, while the Kashiwagura tunnel, built in 1893, is singled out for using brick throughout, down to the coping and string course of its portal.

The two ends need not match

Every tunnel has two portals, and they are frequently different. The Funagatani tunnel in Fukui Prefecture is described as having stone portals, with the northern one carefully sloped at the top to follow the hillside above it.

The Iradani tunnel on the same line, from about 1895, is described as brick in both lining and portals, with dressed stone at the keystone, coping and string course, and its portals given different shapes at either end in response to a site cut through the foot of a mountain.

When writing about one of these, say which end is meant. Material and shape can differ between the two, and a single photograph rarely represents the whole structure.