CHAPTER VI.

_Conclusions._

The writer in concluding this study wishes to emphasize certain principles and apparently minor details of construction, which from observation and personal experience, seem to him of vital importance.

He believes firmly in the truth contained in the following remarks by Mr. Desmond FitzGerald, of Boston, germane to this subject:

An engineer must be guided by local conditions and the resources at his command in building reservoir embankments. His design must be largely affected by the nature of the materials. There are certain _general principles_, however, which must be observed and which will be applied by an engineer of skill, judgment and experience to whatever design he may adopt. It is in the application of these principles that the services of the professional man becomes valuable, and it is from a lack of them, that there have been so many failures.

The details and principles of construction, relating to high earth dams, may be summarized or stated in order of their application, as follows:

(1) Select a firm, dry, impermeable foundation, or make it so by excavation and drainage. All alluvial soil containing organic matter and all porous materials should be excavated and removed from the dam site when practicable; that is, where the depth to a suitable impermeable foundation is not prohibitive by reason of excessive cost.

Wherever springs of water appear, they must be carried outside the lines of the embankment by means of bed rock drains, or a system of pipes so laid and embedded as to be permanent and effective.

The drainage system must be so designed as to prevent the infiltration of water upward and into the lower half of the embankment, and at the same time insure free and speedy outlet for any seepage water passing the upper half. All drains should be placed upon bed rock or in the natural formation selected for the foundation of the superstructure. They should be constructed in such a manner as to prevent the flow of water outside the channel provided for it, and also prevent any enlargement of the channel itself. To this end, cement, mortar, broken stone, and good gravel puddle are the materials best suited for this purpose.

(2) Unite the body of the embankment to the natural foundation by means of an impervious material, durable and yet sufficiently elastic to bond the two together. When the depth to a suitable foundation is great, a central trench excavated with sloping sides, extending to bed rock or other impervious formation, refilled with good puddling material, properly compacted, will suffice.

When clayey earth is scarce and expensive to obtain, a small amount of clay puddle confined between walls of brick, stone or concrete masonry, and extending well into the body of the embankment and so built as to avoid settlement, will prevent excessive seepage. This form of construction is not to be carried much above the original surface of the ground.

(3) The continuity of surfaces should always be broken, at the same time avoiding the formation of cavities and lines of cleavage. No excavation to be refilled should have vertical sides, and long continuous horizontal planes should be intercepted by wedge-shaped offsets, enabling the dovetailing of materials together.

All loose and seamy rock or other porous material should be removed, and where the refill is not the best for the purpose, mix the good and bad ingredients thoroughly, after which deposit in very thin layers.

(4) Make the dimensions and profile of dam with a factor of safety against sliding of not less than ten. The preliminary calculations for designing such a profile have been given on p. 42.

(5) Aim at as nearly a homogeneous mass in the body of the embankment as possible, thus avoiding unequal settlement and deformation. This manner of manipulating materials will eliminate many uncertain or unknown factors, but it means rigid inspection of the work and intelligent segregation of materials, no matter what method of transporting them may be adopted. The smaller the unit loads may be, the more easily a homogeneous distribution of materials will be obtained.

(6) Select earthy materials in preference to organic soils, with a view of such combination or proportion of different materials as will readily consolidate. _Consolidation is the most important process connected with the building of an earth dam._ The judicious use of soil containing a small percentage of organic matter may be permitted, however, when there is a lack of clayey material for mixing with sandy and porous earth materials. Such a mixture, properly distributed and wetted, will consolidate well under heavy pressure and prove quite satisfactory.

(7) Consolidation being the most important process and the only safeguard against permeability and instability of form, use only the amount of water necessary to attain this. Too much or too little are equally bad and to be avoided. It is believed that only by experiment and experience is it possible to determine just the proper quantity of water to use with the different classes of materials and their varying conditions. In rolling and consolidating the bank, all portions that have a tendency to quake must be removed at once and replaced with material that will consolidate; it _must not_ be covered up, no matter how small the area.

(8) In an artificial embankment for impounding water it is impracticable to place reliance upon time for consolidation; it _must_ be effected by mechanical means. Again we repeat, that consolidation is the most vitally important operation connected with the building of an earth dam. When this is satisfactorily attained it is proof that the materials are suitable and that the other necessary details have been in a large measure complied with. Light rollers are worse than useless, being a positive harm, resulting in a smoothing or “ironing process,” deceptive in appearance and detrimental in many ways.

The matter of supreme importance in the construction of earth dams is that the greatest consolidation possible be specified and effected. To this end it is necessary that heavy rollers be employed, and that such materials be selected as respond best to the treatment. There are certain kinds of earth materials which no amount of wetting and rolling will compact. These must be rejected as unfit for use in any portion of an earth dam. Let the design of the structure be ever so true to correct engineering principles, it is still necessary to give untiring attention to the work of consolidation. It is therefore according to the design of a thoroughly compacted homogeneous mass, rather than to the suggested _diaphragm type_, to which modern practice should conform. This is in harmony with Nature’s own methods, and in conformity to correct principles.

(9) Avoid placing pipes or culverts through any portion of the embankment. The writer considers it bad practice ever to place the outlet pipes through a high earth dam, and fails to see any necessity for so doing.

(10) The surface of the dam, both front and rear, must be suitably protected against the deteriorating effects of the elements. This may include pitching the up-stream face, the riprap work at the toe of the inner slope, the roadway and covering of the crown, the sodding or other protection of the rear slope, and the construction of surface drains for the berms.

(11) Ample provision for automatic wasteways should be made for every dam, so that the embankment can never under any circumstances be over-topped by the impounded water. Earthquakes and seismic disturbances will produce no disastrous effects upon an earth dam. Its elasticity will resist the shock of water lashing backwards and forwards in the reservoir.

(12) Finally, provide for intelligent and honest supervision during construction, and insist upon proper care and maintenance ever afterwards.

APPENDIX I.

High Earth Dams.

–Embankment– ––– Slopes ––– Available Name of Dam Max. Top depths, or Reservoir. Location. height, width, Water. Bear. ft. ft. ft.

San Leandro California 125 28 Tabeaud California 123 20 3 on 1 2½ on 1 70 Druid Hill Maryland 119 60 4 on 1 2 on 1 82 Dodder Ireland 115 22 3½ on 1 3 on 1 Titicus Dam New York 110 30 2 on 1 2½ on 1 Mudduk Tank India 108 3 on 1 2½ on 1 Cummum Tank India 102 3 on 1 1 on 1 90 Dale Dike England 102 12 2½ on 1 2½ on 1 Marengo Algeria 101 Torside England 100 84 Yarrow England 100 24 3 on 1 2 on 1 Honey Lake California 96 20 3 on 1 2 on 1 Pilarcitos California 95 25 2¾ on 1 2½ on 1 San Andres California 95 25 3½ on 1 3 on 1 Temescal California 95 12 3 on 1 2 on 1 Waghad India 95 6 3 on 1 2 on 1 81 Bradfield England 95 12 2½ on 1 2½ on 1 Oued Menrad Algeria 95 St. Andrews Ireland 93 25 Edgelaw Scotland 93 3 on 1 2½ on 1 Woodhead England 90 72 Tordoff Scotland 85 10 3 on 1 2½ on 1 Naggar India 84 Vahar India 84 24 3 on 1 2½ on 1 Rosebery Scotland 84 Atlanta Georgia 82 40 Roddlesworth England 80 16 3 on 1 2½ on 1 68 Gladhouse Scotland 79 12 3 on 1 2½ on 1 68½ Rake England 78 3 on 1 2 on 1 Silsden England 78 3 on 1 2 on 1 Glencourse Scotland 77 3 on 1 58 Leeshaw England 77 Wayoh England 76 22 3 on 1 2½ on 1 Ekruk Tank India 76 20 3 on 1 2 on 1 65 Nehr India 74 8 Middle Branch New York 73 Leeming Ireland 73 10 3 on 1 2 on 1 50 South Fork Penna. 72 20 2 on 1 1½ on 1 50 Anasagur India 70 20 4 on 1 Pangran India 68 8 42 Harlaw Scotland 67 64 Lough Vartry Ireland 66 28 3 on 1 2½ on 1 60 La Mesa California 66 20 1½ on 1 1½ on 1 60 Amsterdam New York 65 Mukti India 65 10 3 on 1 2 on 1 41 Snake River California 64 12 2 on 1 1½ on 1 Stubken Ireland 63 24 3 on 1 2 on 1 Den of Ogil Scotland 60 50 Loganlea Scotland 59 10 3 on 1 2½ on 1 55 Ashti India 58 6 3 on 1 2 on 1 42 Cedar Grove New Jersey 55 18 3 on 1 2 on 1 50

APPENDIX--II.

Works of Reference.

Author. Title. Date. Baker, Benj. The Actual Lateral Pressure of Earthwork 1881 Baker, Ira O. Treatise on Masonry Construction 1899 Bell, Thos. J. History of the Water Supply of the World 1882 Beloe, Chas. H. Beloe on Reservoirs 1872 Bowie, Aug. J., Jr. A Practical Treatise on Hydraulic Mining 1898 Brant, Wm. J. Scientific Examination of Soils 1892 Brightmore, A. M. The Principles of Water-Works Engineering 1893 Buckley, Robt. B. Irrigation Works in India and Egypt 1893 Cain, Wm. Retaining Walls 1888 Chittenden, H. M. Report and Examination of Reservoir Sites in Wyoming and Colorado 1898 Courtney, C. F. Masonry Dams 1897 Fanning, J. T. Water-Supply Engineering 1889 Flynn, P. J. Irrigation Canals and Other Irrigation Works 1892 Frizell, Jos. P. Water Power 1891 Gordon, H. A. Mining and Mining Engineering 1894 Gould, E. S. The Elements of Water-Supply Engineering 1899 Hall, Wm. Ham. Irrigation in California 1888 Hazen, Allen The Filtration of Public Water Supplies 1895 Howe, M. A. Retaining Walls for Earth 1891 Hughes, Saml. Treatise on Water-Works 1856 Jackson, L. D. A. Statistics of Hydraulic Works 1885 Kirkwood, J. P. Filtration of River Waters 1869 Merriman, M. Treatise on Hydraulics, Masonry Dams and Retaining Walls 1892 Newell, F. H. Irrigation in the United States 1902 Newman, John Earthwork Slips and Subsidences Upon Public Works 1890 Potter, Thomas Concrete 1894 Schuyler, J. D. Reservoirs for Irrigation, Water Power and Domestic Water Supply 1901 Slagg, Chas. Water Engineering 1888 Stearns, F. P. Metropolitan Water-Works Reports 1897 Stockbridge, H. E. Rocks and Soils 1888 Trautwine, J. C. Earthwork; and Engineer’s Pocket-Book 1890 Turner, J. H. T. The Principles of Water-Works Engineering 1893 Wilson, J. M. Manual of Irrigation Engineering 1893

Annual Reports.

Massachusetts State Board of Health. Geological Survey of New Jersey. Metropolitan Water-Works, Boston and vicinity. U. S. Geological Survey. Transactions American Society of Civil Engineers. Vols. 3, 15, 24, 32, 34 and 35. Proceedings of the Institution of Civil Engineers. Vols. 59, 62, 65, 66, 71, 73, 74, 76, 80, 115 and 132. Engineering News. Vols. 19 to 46. Engineering Record. Vols. 23 to 46. Journal of the Association Engineering Societies. Vol. 13.

INDEX.

Analyses, soil, Tabeaud Dam, 25 Analyses of soils, 14 Tabeaud Dam, 25 Borings, wash drill, Wachusett Dam, 48

Catchment area, 3 Clay for puddle, 15 Contractors’ outfit, Tabeaud Dam, 31 Core wall, impervious diaphragm as substitute for, 62 necessity for, 44 (See puddle.)

Dam, Ashti, India, 35 Bog Brook, 41 Bohio, Panama Canal, 54 Croton Valley, slope of saturation in, 40 different types of earth, 33 Druid Lake, Baltimore, 52 high earth, statistical table of, 67 hydraulic-fill, 61 hydraulic-fill, San Leandro, 60 ideal profile of, 42 Isthmian Canal Commission, 54 Lake Frances hydraulic-fill, 61 New Croton, 39 graphical study of original earth portion of, 43 New England, typical section of, 40 new types of, 54 North Dike, Wachusett Reservoir, 48 rock-fill and earth combined, upper Pecos River, 58 safe height of, 39 San Leandro, 58 site location, 7 Tabeaud, 13, 17 Titicus, 41 Upper Pecos River rock-fill and earth, 58 with puddle core wall or face, 33 Yarrow, Liverpool water-works, 9, 33 Diaphragms impervious for earth dams, 62, 65 Dike, north of Wachusett Reservoir (see Dam; also reservoir) Drainage and slips of earthwork, 45 of dam sites, 63 Drains, bed rock, Tabeaud Dam, 19

Earthwork slips and drainage, 45 Embankment, Ashti, India, 35 Embankments, Jerome Park Reservoir, 45, 46

Factor of safety for dams, 64 Filtration, experiments on nitration through soils at Wachusett Reservoir, 50 formula, Hazen’s, 56 Foundations, 9, 63

Gravel for puddle, 15

Infiltration and percolation, 38 Isthmian Canal Commission, designs of dams for, 54

Outlet pipes and tunnels, 6

Percolation, 38, 57 Profile, ideal for dams, 42 Puddle, 14 core wall, Ashti Dam, 35 or face, 33 trench, 37 wall, Druid Lake Dam, 53 for Yarrow Dam, 34 vs. puddle face, 37

Reservoir basin, 37 outlets, 6 Wachusett, 48 Rollers for dams, 30, 65

Sands and gravels, flow of water through, 52 (Also see percolation.) Slips and drainage of earthwork, 45 Soil analyses, Tabeaud Dam, 25 analysis, 14 Soils, experiments on filtration through at Wachusett Reservoir, 50 outline study of, 12 permanence of, 51 selection of, for dams, 64 studies, Wachusett Reservoir, 50 Spillway or wasteway, 8 Tabeaud Dam, 31 Subsidences, earthwork, 45

Test pits, 5, 8, 9 Tunnel, outlet, Tabeaud Dam, 30 Tunnels as outlets to reservoirs, 6

Wasteway or spillway, 8, 66 Tabeaud Dam, 31

FOOTNOTES:

[1] The writer had intended to present a table of physical properties of different materials, giving their specific gravity, weight, coefficient of friction, angle of repose, percentage of imbibition, percentage of voids, etc., but found it impossible to harmonize the various classifications of materials given by different authorities.

[2] The effective head at any point of an earth dam has been defined as the difference in the elevation of the high-water surface in the reservoir and that of the intersection of the down-stream slope with the natural or restored surface of the ground below the dam.

[3] This work is very fully described in the Annual Reports of the Metropolitan Water Board of Boston; and by Mr. F. P. Stearns, Chief Engineer of the Metropolitan Water and Sewerage Board, in the Proceedings of the American Society of Civil Engineers for April, 1902. The latter description was reprinted, with the omission of some of the illustrations, in Engineering News for May 8, 1902.

[4] By effective size of sand grains is meant such size of grain that 10% by weight of the particles are smaller, and 90% larger than itself; or, to express it a little differently, the effective size is equal to a sphere the volume of which is greater than ¹/₁₀ that forming the weight and is less than ⁹/₁₀ that forming the weight.

[5] The term “uniformity coefficient” is used to designate the ratio of the size of the grain which has 60% of the sample finer than itself to the size which has 10% finer than itself. The method of determining the size of sand grains and their uniformity coefficients, is fully explained in Appendix 3 of Mr. Hazen’s book on “The Filtration of Public Water Supplies.”