102 — ANNUAL REPORT 
Fig. 46.—Otay Dam, Showing Contractor’s Plant, San Diego, Cal. 
ular stones are imbedded. (Figure 47.) These stones make about one- 
half of the volume of the dam. Such cyclopean masonry might be termed 
titanic concrete. 
The opportunity to reduce in cost of construction by adopting open 
or buttressed sections in concrete, such as are described elsewhere in this 
article, will bring concrete more prominently to the front in the future 
than it has been in the past for large dams. 
Apple River Dam.—Another feature of concrete is in the facing of 
old masonry dams or soft stone masonry cores in new dams. The Apple 
River dam for the St. Croix Power Company of St. Paul, Minn., illus- 
trates its use in the latter form. This dam erected across the Apple River 
about 27 miles east of St. Paul, was in a very rough country where the 
only available building stone was a brown sandstone easily eroded by run- 
ning water. It was decided to erect the core of the dam of this sand- 
stone laid as uncoursed rubble with Portland cement mortar, composed 
of I part cement to 3 parts sand. This core was then encased with from 
18 inches to 2 feet of concrete having the following proportions: 1 part 
Portland cement, 3 parts sand and 4 parts broken stone. The dam is 350 
feet long with a central spillway 108 feet long over the crest of the dam. 
The dam is built in arch form up stream with radius of curvature equal 
to 450 feet. It is 47 feet high and has a base width or thickness of 38 
feet. No cracks or leakage had appeared after a year’s service. Figure 
48 shows a cross section of the dam. 
