(For profile, cross-section, and plan see the following page.)
The dam is to consist of two piles of rock 1,200 feet apart and carried up to 60 feet above mean tide with the space between them and up to 115 feet above sea-level filled by selected material deposited in place by the hydraulic process. A slip occurred at one of these rock toes during November, 1908, and caused considerable alarm throughout the country, so much, in fact, that the President sent W. H. Taft with a group of 7 noted engineers to investigate. They reported that “A full study of all the data and of the material, and of the plans that are proposed leaves no doubt in our minds as to the safe, tight, and durable character of the Gatun dam”.
At the close of the fiscal year 1908–’09 three 20-inch suction dredges were depositing material over the area between the rock piles, and the fill had reached an average elevation of 16 feet above sea-level. A total of 2,501,372 cubic yards was placed in the dam during the year.
Excavation through the Spillway Hill was practically completed and 30,464 cubic yards of concrete laid. During the year 359,821 cubic yards of material were removed from Spillway hill by steam shovels and placed on the dam.
The original canal plans provided for a flight of two locks at La Boca, near the Pacific, and one at Pedro Miguel. Steps were taken to construct the former and trestles were built along the toes from which to dump material from Culebra Cut. The trestles failed after dumping began and material overlying the rock moved laterally, the movement continuing for two weeks in some places. After this result these dams were abandoned so that instead of locks at La Boca they will be built at Miraflores. Another reason for the change besides poor foundations is the military advantages of the latter over the former position.
Both the dams at Pedro Miguel and Miraflores will be constructed of two rock piles, the portion between being filled by hydraulic methods. Very little work has been done upon them.
FIG. 3.—PROFILE ON THE AXIS OF THE GATUN DAM SITE SHOWING UNDERLYING MATERIAL AS DETERMINED BY BORING.
(From Report of C. M. Saville, Assistant Engineer, August 29, 1908.)
