Puddle.
Puddle without qualification may be defined as clayey and gravelly earth thoroughly wetted and mixed, having a consistency of stiff mud or mortar. Puddle in which the predominating ingredient of the mixture is pure clay, is called clay puddle. Gravel puddle contains a much higher percentage of grit and gravel than the last-named and yet is supposed to have enough clayey material to bind the matrix together and to fill all the voids in the gravel.
The term earthen concrete may also be applied to this class of material, especially when only a small quantity of water is used in the mixture. These different kinds of puddling materials may be found in natural deposits ready for use, only requiring the addition of the proper amount of water. It is usually necessary, however, to mix, artificially, or combine the different ingredients in order to obtain the right proportions. Some engineers think grinding in a pug-mill absolutely essential to obtain satisfactory results.
Puddle is handled very much as cement concrete, which is so well understood that detailed description is hardly necessary. Instead of tampers, sharp cutting implements are usually employed in putting puddle into place. Trampling with hoofed animals is frequently resorted to, both for the purpose of mixing and compacting.
As has been stated, clays come from the decomposition of crystaline rocks. The purest clay known (kaolin) is composed of alumina, silica and water. The smaller the proportion of silica the more water it will absorb and retain. Dry clay will absorb nearly one-third of its weight of water, and clay in a naturally moist condition 1-6 to 1-8 its weight of water. The eminent English engineers, Baker and Latham, put the percentage of absorption by clayey soils as high as 40 to 60%. Pure clays shrink about 5% in drying, while a mixture by weight of 1 clay to 2 sand will shrink about 3%. It follows, then, that the larger the percentage of clay there may be in a mixture the greater will be both the expansion and the contraction.
Clay materials may be very deceptive in some of their physical properties, being hard to pick under certain conditions, and yet when exposed to air and water will rapidly disintegrate. Beds of clay, marl and very fine sand are liable to slip when saturated, becoming semi-fluid in their nature, and will run like cream.
The cohesive and frictional resistances of clays becoming thus very much reduced when charged with water, a too liberal use of this material is to be deprecated. The ultimate particles forming clays, viewed under the microscope, are seen to be flat and scale-like, while those of sands are more cubical and spherical. This is a mechanical difference which ought to be apparent to even a superficial observer and yet has escaped recognition by many who have vainly attempted a definition of quicksand.
Mr. Strange recommends filling the puddle trench with material having three parts soil and two parts sand. After the first layer next to bed rock foundation, which he kneads and compacts, he would put the layers in dry, then water and work it by treading, finally covering to avoid its drying out and cracking.
Prof. Philipp Forchheimer, of Gratz, Austria, one of the highest authorities and experimentalists, affirms that if a sandy soil contains clay to such an extent that the clay fills up the interstices between the grains of sand entirely the compound is practically impervious.
Mr. Herbert M. Wilson, C. E., in his “Manual of Irrigation Engineering,” recommends the following as an ideal mixture of materials:
| Cu. yds. | |
| Coarse gravel | 1.00 |
| Fine gravel | 0.35 |
| Sand | 0.15 |
| Clay | 0.20 |
| Total | 1.70 |
This mixture, when rolled and compacted, should give 1.25 cu. yds. in bulk, thus resulting in 26½% compression.
Mr. Clemens Herschel suggests the following test of “good binding gravel:” “Mix with water in a pail to the consistency of moist earth; if on turning the pail upside down the gravel remains in the pail it is fit for use, otherwise it is to be rejected.” For puddling material he would use such a proportion as will render the water invisible.
CHAPTER IV.
The Tabeaud Dam,
California.
The Tabeaud Dam, in Amador County, Cal., built under the supervision of the author for the Standard Electric Co., is an example of the homogeneous earth dam. A somewhat fuller description and discussion will be given of this dam than of any other, not on account of its greater importance or interest, but because it exemplifies certain principles of construction upon which it is desired to put special emphasis. This dam was described in Engineering News of July 10, 1902, to which the reader is referred for more complete information than is given here.
FIG. 3.–PLAN OF TABEAUD RESERVOIR, WITH CONTOURS.
FIG. 4.–PLAN OF TABEAUD DAM, SHOWING BED ROCK DRAINAGE SYSTEM.
FIG. 5.–DETAILS OF BED ROCK DRAINS AT THE TABEAUD DAM.
[Fig. 3] is a contour map of the Tabeaud Reservoir, showing the relative locations of the dam, wasteway and outlet tunnel. [Fig. 4] shows the bed rock drainage system and the letters upon the drawing will assist in following the explanation given in the text. The whole up-stream half of the dam site was stripped to bed rock. As the work of excavation advanced pockets of loose alluvial soil were encountered, which were suggestive of a refill, possibly the result of placer mining operations during the early mining days of California. In addition to this were found thin strata of sand and gravel deposited in an unconformable manner. The slate bed rock near the up-stream toe of the dam was badly fissured and yielded considerable water. A quartz vein from 1 to 2 ft. in thickness crossed the dam site about 150 ft. above the axis of the dam. The slate rock above this vein or fault line was quite variable in hardness and dipped at an angle of 40 degrees toward the reservoir.
FIG. 6.–VIEW OF BED ROCK TRENCHES, TABEAUD DAM.
The rear drain terminates at a weir box (Z) outside of the down-stream slope at a distance of 500 ft. from the axis of the dam. This drain branches at the down-stream side of the central trench, (Y), one branch being carried up the hillside to high-water level (W) at the North end of the dam, and the other to the same elevation at the South end (X).
[Fig. 5] shows how these drains were constructed. After the removal of all surface soil and loose rock, a trench 5 to 10 ft. wide was cut into the solid rock, the depth of cutting varying with the character of the bed rock. Upon the floor of this trench a small open drain was made by notching the bed rock and by means of selected stones of suitable size and hardness. The stringers and cap-stones were carefully selected and laid, so that no undue settlement or displacement might occur by reason of the superincumbent weight of the dam. All crevices were carefully filled with spawls and the whole overlaid 18 ins. in depth with broken stone 1 to 3 ins. in diameter. Upon this layer of broken stone and fine gravel was deposited choice clay puddle, thoroughly wetted and compacted, refilling the trenches.
FIG. 7.–VIEW OF NORTH TRENCH, TABEAUD DAM.
FIG. 8.–VIEW OF SOUTH TRENCH, TABEAUD DAM.
FIG. 9.–VIEW OF MAIN CENTRAL DRAIN, TABEAUD DAM.
These drains served a useful purpose during construction, in drying off the surface of the dam after rains. The saturation of the outer slope of the dam by water creeping along the line of contact should thus be prevented, and the integrity or freedom from saturation of the down-stream half should be preserved. It is believed that the puddle overlying these rock drains will effectually prevent any water from entering the body of the embankment by upward pressure and that the drains will thus forever act as efficient safeguards.
The main drain was extended, temporarily during construction, from the central trench ([Fig. 4]), to the up-stream toe of the dam. This was cut 5 or 6 ft. deep into solid rock, below the general level of the stripped surface. [Fig. 6] is reproduced from a photograph of this trench. An iron pipe 2 ins. in diameter was imbedded in Portland cement mortar and concrete, and laid near the bottom of the trench.
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 dry | 84.0 |
| ““ 1 “ | saturated earth | 101.8 |
| ““ 1 “ | moist loose earth | 76.6 |
| ““ 1 “ | loose material taken from test pits on the dam | 80.0 |
| ““ 1 “ | earth in place taken from the borrow pits | 116.5 |
| ““ 1 “ | earth material taken from test pits on the dam | 133.0 |
| Per cent. | ||
| Percentage of | moisture in natural earth | 19 |
| “ “ | voids in natural earth | 52 |
| “ “ | grit and gravel in natural earth | 38 |
| “ “ | compression on dam over earth at borrow pit | 16 |
| “ “ | compression on dam over earth in wagons | 43 |
| Degrees. | |
| Angle of repose of natural moist earth | 44 |
| Angle of repose of earth, dust dry | 36 |
| Angle of repose of saturated earth | 23 |
CONSTRUCTION DETAILS.–The materials forming the bulk of the dam were hauled by four-horse teams, in dump wagons, holding 3 cu. yds. each. The wagons loaded weighed about six tons and were provided with two swinging bottom-doors, which the driver could operate with a lever, enabling the load to be quickly dropped while the team was in motion. If the material was quite dry, the load could be dumped in a long row when so desired.
After plowing the surface of the ground and wasting any objectionable surface soil, the material was brought to common earth-traps for loading into wagons, by buck or dragscrapers of the Fresno pattern. In good material one trap with eight Fresno-scraper teams could fill 25 wagons per hour. The average length of haul for the entire work was about 1,320 ft.
The original plans and specifications were adhered to throughout, with the single exception that the central puddle wall was not carried above elevation 1,160, as shown on [Figs. 11] and [12], more attention being given to the inner face puddle. This modification in the original plans was made because of the character of the materials available and the excellent results obtained in securing an homogeneous earthen concrete, practically impervious.
FIG. 11.–DIMENSION SECTION OF TABEAUD DAM.
The top of the embankment was maintained basin-shaped during construction, being lower at the axis than at the outer slopes by 1-10, to the height below the finished crown. This gave a grade of about 1 in 25 from the edges toward the center, resulting in the following advantages:
(1) Insuring a more thorough wetting of the central portion of the dam; any excess of water in this part would be readily taken care of by the central cross drains.
(2) In wetting the finished surface prior to depositing a new layer of material, water from the sprinkling wagons would naturally drain towards the center and insure keeping the surface wet; the layers being carried, as a rule, progressively outward from the center.
(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.
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.
Two rollers were in use constantly, each drawn by six horses. One weighed five tons and the other eight tons, giving respectively 166 and 200 lbs. pressure per lin. in. They were not grooved, but the smooth surface left by the rollers was always harrowed and cut up more or less by the loaded wagons passing over the surface previously wetted. The wagons when loaded gave 750 lbs. pressure per lin. in., and the heavy teams traveling wherever they could do the most effective work compacted the materials better even than the rollers.
Several test pits which were dug into the dam during construction showed that there were no distinct lines traceable between the layers and no loose or dry spots, but that the whole mass was solid and homogeneous.
A careful record is being kept of the amount of settlement of the Tabeaud Dam. It will be of interest to record here the fact that just one year after date of completion the settlement amounted to 0.2 ft., with 90 ft. depth of water in the reservoir.
Water was first turned into the reservoir five months after the dam was finished. The very small amount of settlement here shown emphasizes more eloquently than words the author’s concluding remarks relating to the importance of thorough consolidation, by artificial means, of the embankment. ([See p. 64, Secs. 6 to 8.])
OUTLET TUNNEL.–The outlet for the reservoir is a tunnel 2,903 ft. in length, through a ridge of solid slate rock formation, which was very hard and refractory. At the north or reservoir end of the tunnel, there is an open cut 350 ft. long, with a maximum depth of 26 ft.
Near the south portal of the tunnel and in the line of pressure pipes connecting the “petty reservoir” above with the power-house below, is placed a receiver, connected with the tunnel by means of a short pipe-line, 60 ins. in diameter.
A water-tight bulkhead of brick and concrete masonry is placed in the tunnel, at a point about 175 ft. distant from the receiver. In the line of 60-in. riveted steel pipe, which connects the reservoir and tunnel with the receiver, there is placed a cast iron chamber for entrapping silt or sand, with a branch pipe 16 ins. in diameter leading into a side ravine through which sand or silt thus collected can be wasted or washed out. By the design of construction thus described, it will be seen that all controlling devices, screens, gates, etc., are at the south end of the tunnel and easily accessible.
WASTEWAY.–The wasteway for the reservoir is an open cut through its rim, 48 ft. in width and 300 ft. long. The sill of the spillway is 10 ft. below the crown of the dam. The reservoir having less than two square miles of catchment area, and the feeding canals being under complete control, the dam can never be over-topped by a flood. [Fig. 3] shows the relative location of the dam, outlet tunnel and wasteway channel.
Almost the whole of the embankment forming the Tabeaud Dam, not included in the foundation work, was built in less than eight months. The contractor’s outfit was the best for the purpose the writer has ever seen. After increasing his force from time to time he finally had the following equipment:
- 1 steam shovel (1½ yds. capacity),
- 37 patent dump wagons,
- 11 stick-wagons and rock-carts,
- 39 buck-scrapers (Fresno pattern),
- 21 wheel scrapers,
- 3 road-graders,
- 3 sprinkling wagons,
- 2 harrows,
- 2 rollers (5 and 8-ton),
- 233 men,
- 416 horses and mules,
- 8 road and hillside plows.
STATISTICS.–The following data relating to the Tabeaud Dam Reservoir will conclude this description:
| DAM. | ||
| Length at crown | 636 | ft. |
| Length at base crossing ravine | 50 to 100 | “ |
| Height to top of crown (El. 1,258.) | 120 | “ |
| “ at ends above bedrock | 117 | “ |
| “ at up-stream toe | 100 | “ |
| “ at down-stream toe | 123 | “ |
| Effective head | 115 | “ |
| Width at crown | 20 | “ |
| Width at base | 620 | “ |
| Slopes, 2½ on 1 with rock-fill 3 to 1. | ||
| Excavation for foundations | 40,000 | cu. yds. |
| Refill by company | 40,000 | “ |
| Embankment built by contractor | 330,350 | “ |
| Total volume of dam | 370,350 | “ |
| Total weight | 664,778 | tons. |
| Length of wasteway (width) | 48 | ft. |
| Depth of spillway sill below crown | 10 | “ |
| Depth of spillway sill below ends | 7 | “ |
| Height of stop-planks in wasteway | 2 | “ |
| Maximum depth of water in reservoir | 92 | “ |
| Area to be faced with stone | 1,933 | sq. yds. |
| RESERVOIR. | ||
| Catchment area (approximate) | 2 | sq. miles. |
| Area of water surface | 36.75 | acres. |
| Silt storage capacity below outlet tunnel | 1,091,470 | cu. ft. |
| Available water storage capacity | 46,612,405 | “ |
| Elevation of outlet tunnel | 1,180 | ft. |
| ““ high-water surface | 1,250 | “ |
| ““ crown of dam | 1,258 | “ |
[Fig. 13] is a view of the finished dam, taken immediately after completion.
CHAPTER V.
Different Types of Earth Dams.
There are several types of earth dams, which may be described as follows:
1. Homogeneous earth dams, either with or without a puddle trench.
2. Earth dams with a puddle core or puddle face.
3. Earth dams with a core wall of brick, rubble or concrete masonry.
4. New types, composite structures.
5. Rock-fill dams with earth inner slope.
6. Hydraulic-fill dams of earth and gravel.
The writer proposes to give an example of each type, with such remarks upon their distinctive features and relative merits as he thinks may be instructive.