Liberty Memorial Bridge

Piers for the Liberty Memorial Bridge are sunk into the Missouri River. The process for sinking the shafts was described in a 1922 Bismarck Tribune article: It is customary to construct a ring of steel or other material. This is built or placed at the exact site where the proposed shaft is to be sunk. The underside of this ring will usually be provided with an edge consisting of a single bevel... This ring is the cutting edge. Above and on this ring is constructed of concrete or other masonry a cylindrical wall. Thus, this tile-shaped structure is placed on the bed of the river. By digging round and round the edge, from the inside, the cutting edge of this "tile" of masonry may be made to descend of its own weight. As this "tile" or "well" sunk of its own weight when the earth was taken out from the inside, another  section was placed on top of it, and another, and so on until the several sections, fastened together as one, had sunk to the complete depth of the pier, or about 50 feet. As the "tile" or "well" went down deeper the air became poorer. Water must be pumped out while the digging goes on... The "well" could be made airtight, and men would work inside of it shoveling out dirt and manning the pumps under compressed air. ... After these tile-shaped, hollow shafts were sunk to the full depth, rocks and concrete were poured in them, until the pier was made one solid mass.