key up
To raise slightly a structure built of, or secured by, keys, by forcing the keys into the prepared spaces. Thus, in an arch, the last voussoir, serving as a key, may be shaped slightly too large and then be driven into place, by which process the entire arch ring is crowned up higher, even to the extent of raising it entirely from the centering. A similar operation is frequently performed at the base of a settled wall which is to be underpinned. (Sturgis, 1900)