At the point (B) where the quartz vein (already described) intersected this drain, two branch drains were made, following the fault well into the hill on both sides. [Figs. 7] and [8] are views of the North and South trenches, respectively. These trenches were necessary to take care of the springs issuing along the quartz vein. This water led to a point ([N, Fig. 4]) near the up-stream toe, by means of the drain shown in [Fig. 9].

The lateral drains and that portion of the main central drain extending from their junction (B) to a point (N) about 230 ft. from the axis of the dam have pieces of angle iron or wooden Y-fluming laid on the bottom of the trenches immediately over the 2-in. pipe, as shown in [Figs. 7], [8] and [9]. These are covered in turn with Portland cement mortar, concrete, clay puddle and earth fill. The water will naturally flow along the line of least resistance, and consequently will follow along the open space between the angle irons and the outside of the pipe until it reaches the chamber and opening in the pipe, permitting the water to enter and be conveyed through the imbedded pipe-line to the rear drain. This point of entry is a small chamber in a solid cross-wall of rich cement mortar, and is the only point where water can enter this pipe-line, the two branches entering the wells and the stand-pipe at their junction (soon to be described) having been closed.

That portion of the foundation between the axis of the dam and the quartz vein, a distance of about 160 ft., was very satisfactory, without fissures or springs of water. In this portion the 2-in. pipe was imbedded in mortar and concrete without angle irons, and the continuity of the trench broken by numerous cross-trenches cut into the rock and filled with concrete and puddle. It is believed that no seepage water will ever pass through this portion of the dam. If any should ever find its way under the puddle and through the bed rock formation, the rear drain, with its hillside branches, will carry it away and prevent the saturation of the lower or down-stream half of the dam.

FIG. 10.–VIEW OF TABEAUD DAM WHEN ABOUT HALF COMPLETED.

At the up-stream toe of the embankment, two wells or sumps ([shown at “S” and “K,” Fig. 4]) were cut 10 or 12 ft. deeper than the main trench, which received the water entering the inner toe puddle trench during construction. This water was disposed of partly by pumping and partly by means of the 2-in. branch pipes leading into and from these wells. At their junction (J) a 2-in. stand-pipe was erected, which was carried vertically up through the embankment, and finally filled with cement. The branch pipes from the wells were finally capped and the wells filled with broken stone, as previously mentioned.

EMBANKMENT.–As has been said, the upper surface of the slate bed rock was found to be badly fissured, especially near the up-stream toe of the dam, and as the average depth below the surface of the ground was not very great, it was thought best to lay bare the bed rock over the entire upper half of the dam site. Had the depth been much greater, it would have been more economical and possibly sufficient to have put reliance in a puddle trench, alone, for securing a water-tight connection between the foundation and the body of the dam.

At the axis of the dam and near the inner toe, where the puddle walls abutted against the hillsides, the excavation always extended to bed rock. Vertical steps and offsets were avoided and the cuts were made large enough for horses to turn in while tramping, these animals being used, singly and in groups, to mix and compact the puddle and thus lessen the labor of tamping by hand. In plan, the hillside contact of natural and artificial surfaces presents a series of corrugated lines, ([as is clearly shown in Fig. 4.]) After all loose and porous materials had been removed, the stripped surface and the slopes of all excavations were thoroughly wetted from time to time by means of hose and nozzle, the water being delivered under pressure. [Fig. 10] is a view of the dam taken when it was about half finished and shows the work in progress.

The face puddle shown in [Fig. 11] was used merely to “make assurance doubly sure” and was not carried entirely up to the top of the dam. The earth of which the dam was constructed may be described as a red gravelly clay, and in the judgment of the author is almost ideal material for the purpose. Physical tests and experiments made with the materials at different times during construction gave the following average results:

Pounds.
Weight of 1 cu. ft.earth, dust dry84.0
““ 1 “saturated earth101.8
““ 1 “moist loose earth76.6
““ 1 “loose material taken from test pits on the dam 80.0
““ 1 “earth in place taken from the borrow pits116.5
““ 1 “earth material taken from test pits on the dam133.0