Coping stone

What a coping stone is

A coping stone is laid horizontally along the top of a wall or a Tunnel portal. It throws rainwater clear so the structure below stays dry, and it draws a firm horizontal line across the top of the elevation.

On a tunnel portal it is listed alongside the pilasters and the string course. The former Hokuriku Line Ashidani tunnel in Fukui Prefecture, built in 1894, is described as having a portal with pilasters, coping and string course, built up throughout in dressed stone.

Good stone tends to be reserved for these positions. 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, the coping and the string course, finished with a fine chamfer along the edges.

The former Chuo Line Tamano Fourth tunnel in Aichi Prefecture, built in 1900, has a brick portal with dressed stone used decoratively at the coping and other key points, a brick structure with stone at the places that matter.

Built in brick instead

Despite the Japanese name, the part is not always stone. The former Hokuriku Line Kashiwagura tunnel in Fukui Prefecture, built in 1893, is described as the work of an engineer who was the first graduate to found a contracting firm, and is singled out for using brick throughout, from the lining to the coping and string course of the portal.

That this is treated as distinctive shows the usual practice. Dressed stone at the coping and string course was the norm, and substituting brick was a departure worth recording.

On site, look at the top of the portal. A horizontal band projecting slightly beyond the wall face is the coping. Stone bridges and brick walls carry the same element for the same reason.