Page:Final Report - The Columbia River Interstate Bridge.pdf/42



A complete description of the processes of construction will not be attempted, but three features which were of special interest deserve some description. These are (1) the method of building the piers and placing the long piles already described; (2) the erection of the superstructure metalwork by building the spans on shore complete and ﬂoating them to the piers; and (3) the construction of the approach embankments by hydraulic dredging.

(1) The plant and equipment supplied by the Paciﬁc Bridge Company were unusual in certain respects and peculiarly adapted to the work in hand. Excavation was made by a dipper

dredge of the shovel type having a 4 cubic yard bucket. an unusual equipment for such work. With this machine a hole was dredged into the river bed at the site of the pier to the full depth required and large enough to let the sides of the excavation take a natural slope. The timber crib enclosing the base of the pier was partly built on launching ways. ﬂoated to position and framed up to full height. A removable cofferdam in one section. used successively on different piers, was then picked up and placed on the crib. the crib sunk to the proper depth in