(3) It centralized the maximum earth pressure and enabled the depositing of material in layers perpendicular to the slopes.
(4) It facilitated rolling and hauling on lines parallel to the axis of the dam, and discouraged transverse and miscellaneous operations.
(5) It finally insured better compacting by the tramping of teams in their exertions to overcome the grade.
FIG. 12.–CROSS AND LONGITUDINAL SECTIONS OF TABEAUD DAM.
The specifications stipulated that the body of the dam should be built up in layers not exceeding 6 ins. in thickness for the first 60 ft., and not exceeding 8 ins. above that elevation. The finished layers after rolling varied slightly in thickness, the daily average per month being as follows:
| April | 4 | ins. |
| May | 3½ | “ |
| June | 4 | “ |
| July | 4½ | “ |
| August | 5 | “ |
| September | 6 | “ |
| October | 7 | “ |
| November and December | 8 | “ |
During the last few months more than one whole layer constituted the day’s work, so that a single layer was seldom as thick as the daily average indicates.
It was stipulated in the specifications that the up-stream half of the dam was to be made of “selected material” and the lower half of less choice material, not designated “waste.” “Waste material” was described as meaning all vegetable humus, light soil, roots, and rock exceeding 5 lbs. in weight, too large to pass through a 4-in. ring.