It may be well to define the expression “selected material,” so commonly used in specifications for earth dams. In England, for instance, it is said to refer to materials which insure water-tightness, while in India it refers to those employed to obtain stability. It ought to mean the best material available, selected by the engineer to suit the requirements of the situation.
The method employed in building the body of the embankment may be described as follows:
(1) The top surface of every finished layer of material was sprinkled and harrowed prior to putting on a new layer. The sprinkling wagons passed over the older finished surface immediately before each wagon-row was begun. This insured a wetted surface and assisted the wheels of the loaded wagons, as well as the harrows, to roughen, the old surface prior to depositing a new layer.
(2) The material was generally deposited in rows parallel to the axis of the dam. However, along the line of contact, at the margins of the embankment, the earth was often deposited in rows crosswise of the dam, permitting a selection of the choicest materials and greatly facilitating the work of graders and rollers.
(3) Rock pickers with their carts were continually passing along the rows gathering up all roots, rocks and other waste materials.
FIG. 13.–VIEW OF TABEAUD DAM IMMEDIATELY AFTER COMPLETION.
(4) The road-graders drawn by six horses leveled down the tops of the wagon-loads, and if the material was dry the sprinkling wagons immediately passed over the rows prior to further grading. When the material was naturally moist the grader continued the leveling process until the earth was evenly spread. The depth or thickness of the layer could be regulated to a nicety by properly spacing the rows and the individual loads. The grader brought the layer to a smooth surface and of uniform thickness, and nothing more could be desired for this operation.
(5) After the graders had finished, the harrows passed over the new layer to insure the picking out of all roots and rocks, followed immediately by the sprinkling wagons.
(6) Finally the rollers thoroughly compacted the layer of earth, generally passing to and fro over it lengthwise of the dam. Along the line of contact at the ends, however, they passed crosswise. Then again they frequently went around a portion of the surface until the whole was hard and solid.