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diff --git a/old/68721-0.txt b/old/68721-0.txt deleted file mode 100644 index 14e5173..0000000 --- a/old/68721-0.txt +++ /dev/null @@ -1,3116 +0,0 @@ -The Project Gutenberg eBook of Earth Dams, A Study, by Burr Bassell - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Earth Dams, A Study - -Author: Burr Bassell - -Release Date: August 9, 2022 [eBook #68721] - -Language: English - -Produced by: Charlene Taylor and the Online Distributed Proofreading - Team at https://www.pgdp.net (This file was produced from - images generously made available by The Internet - Archive/American Libraries.) - -*** START OF THE PROJECT GUTENBERG EBOOK EARTH DAMS, A STUDY *** - - - - - -Transcriber’s Notes: - - Underscores “_” before and after a word or phrase indicate _italics_ - in the original text. - Small capitals have been converted to SOLID capitals. - Illustrations have been moved so they do not break up paragraphs. - Typographical and punctuation errors have been silently corrected. - - - - - EARTH DAMS - _A STUDY_ - - BY - BURR BASSELL, M. Am. Soc. C. E. - _Consulting Engineer_ - - NEW YORK - THE ENGINEERING NEWS PUBLISHING COMPANY - 1904 - - COPYRIGHT, 1904 - BY - THE ENGINEERING NEWS PUBLISHING CO. - - - - -ACKNOWLEDGMENTS. - - -The writer wishes to acknowledge his appreciation of the assistance -given him by Mr. Jas. D. Schuyler, M. Am. Soc. C. E., Consulting -Hydraulic Engineer, in reviewing this paper, and in making suggestions -of value. Appendix II contains a list of authors whose writings have -been freely consulted, and to whom the writer is indebted; the numerous -citations in the body of the paper further indicate the obligations of -the writer. - - - - -CONTENTS. - - - PAGE - CHAPTER I. - Introductory 1 - - CHAPTER II. - Preliminary Studies and Investigations 3 - - CHAPTER III. - Outline Study of Soils. Puddle 12 - - CHAPTER IV. - The Tabeaud Dam, California 17 - - CHAPTER V. - Different Types of Earth Dams 33 - - CHAPTER VI. - Conclusions 63 - - APPENDIX I. - Statistical Descriptions of High Earth Dams 67 - - APPENDIX II. - Works of Reference 68 - - - - -ILLUSTRATIONS. - - - PAGE - Fig. 1. Longitudinal Section of Yarrow Dam Site 10 - 2. Cross-Section of the Yarrow Dam 10 - 3. Plan of the Tabeaud Reservoir 17 - 4. Tabeaud Dam: Plan Showing Bed Rock Drains 18 - 5. Details of Drains 18 - 6. View of Drains 19 - 7. North Trench 20 - 8. South Trench 21 - 9. Main Central Drain 21 - 10. Embankment Work 23 - 11. Dimension Section 26 - 12. Cross and Longitudinal Sections 27 - 13. View of Dam Immediately After Completion 29 - 14. Cross-Section of Pilarcitos Dam 34 - 15. San Andres Dam 34 - 16. Ashti Tank Embankment 35 - 17. Typical New England Dam 40 - 18. Two Croton Valley Dams Showing Saturation 41 - 19. Studies of Board of Experts on the Original Earth - Portion of the New Croton Dam 43 - 20. Studies of Jerome Park Reservoir Embankment 46 - 21 to 24. Experimental Dikes and Cylinder Employed - in Studies for the North Dike of the Wachusett - Reservoir 49 - 25. Cross-Section of Dike of Wachusett Reservoir 49 - 26. Working Cross-Section of Druid Lake Dam 53 - 27 to 29. Designs for the Bohio Dam, Panama Canal 55 - 30. Cross-Section of the Upper Pecos River Rock-Fill Dam 59 - 31. Developed Section of the San Leandro Dam 59 - - - - -EARTH DAMS - - - - -CHAPTER I. - -_Introductory._ - - -The earth dam is probably the oldest type of dam in existence, -antedating the Christian Era many hundreds of years. The literature -upon this subject is voluminous, but much of it is inaccessible and -far from satisfactory. No attempt will here be made to collate this -literature or to give a history of the construction of earth dams, -however interesting such an account might be. The object will rather -be to present such a study as will make clear the application of the -principles underlying the proper design and erection of this class -of structures. In no way, therefore, will it assume the character or -dignity of a technical treatise. - -Dams forming storage reservoirs, which are intended to impound large -volumes of water, must necessarily be built of considerable height, -except in a very few instances where favorable sites may exist. Recent -discussions would indicate that a new interest has been awakened in -the construction of high earth dams. As related to the general subject -of storage, it is with the high structure rather than the low that -this study has to do. To the extent that “the greater includes the -less,” the principles here presented are applicable to works of minor -importance. - -Many persons who should know better place little importance upon -the skill required for the construction of earthwork embankments, -considering the work to involve no scientific problems. It is far -too common belief that any ordinary laborer, who may be able to use -skillfully a scraper on a country road, is fitted to superintend -the construction of an earth dam. It has been said that the art of -constructing earth dams is purely empirical, that exact science -furnishes no approved method of determining their internal stresses, -and that in regard to their design experience is much more valuable -than theory. When the question of stability is fully taken into -consideration, it certainly requires a large amount of skill -successfully to carry out works of this character. - -Extreme care in the selection of the site, sound judgment in the -choice of materials and assiduity in superintending the work while in -progress, are all vitally essential. - - -Classification of Dams. - -Dams may be classified according to their purpose as diverting dams or -weirs and as storage dams. The former may be located upon any portion -of a stream where the conditions are favorable, and the water used for -manifold purposes, being conveyed by means of canals, flumes, tunnels -and pipe-lines to places of intended use. These dams are generally low -and may be either of a temporary or permanent character, depending upon -the uses to which the water is put. Temporary dams are made of brush, -logs, sand bags, gravel and loose rock. The more permanent structures -are built of stone and concrete masonry. - -Storage dams may be classified according to the kind of material -entering into their structure, as follows: (1) Earth; (2) Earth and -Timber; (3) Earth and Rock-fill; (4) Rock-fill; (5) Masonry; (6) -Composite Structures. - -Low dams forming service reservoirs for domestic water supplies and -for irrigation comprise by far the most numerous class. They are not -designed to impound a large volume of water and therefore may be built -across a small ravine or depression, or even upon the summit of a hill, -by excavating the reservoir basin and using the material excavated to -form the embankment. These reservoirs may be used in connection with -surface or gravity systems, artesian wells, or underground supplies -obtained by pumping. The dams forming these reservoirs being of -moderate size and height may vary greatly in shape and dimensions. -The form may be made to suit the configuration of the dam site. When -the earthwork requires it, they may be lined with various materials -to secure water-tightness. Often such dams are made composite in -character, partly of earth and partly of masonry or some other -material. They are also frequently accompanied by numerous accessories, -such as settling-basins, aerating devices and covers, which present a -diversity in form and appearance. A presentation of the different types -of dams thus employed, with a discussion of the questions pertaining -to utility in design and economy in construction, would be exceedingly -valuable and of general interest. Service reservoirs will receive only -a passing notice, with the hope expressed that some competent authority -will discuss them in the future. - - - - -CHAPTER II. - -_Preliminary Studies and Investigations._ - - -The preliminary studies and investigations which should be made prior -to the construction of any dam for the storage of water have to do with -(1) the Catchment Area, (2) the Reservoir basin, and (3) the Dam site. - - -Catchment Area. - -It is thought desirable to define a number of terms as we proceed, -for the purpose of correcting erroneous usage and for a clearer -understanding of the subject. The catchment area of a reservoir is that -portion of the country naturally draining into it. The watershed is -the boundary of the catchment area and may be correctly defined as the -divide between adjacent drainage systems. In regard to the catchment -area it is necessary to determine: - - 1. Its extent and area in square miles. - - 2. Its topography or the character of its surface. - - 3. Its hydrography or precipitation and run-off. - - 4. Its geology, or the character of its soils and subsoils, - and the nature and dip of its rock strata. - - 5. Its flora, or the extent to which it is clothed with forest - trees or other vegetation. - -All of these elements affect the volumes of maximum run-off, which is -the one important factor in the construction of earth dams that must -not be underestimated. - -If the proposed dam or reservoir is to be located upon a main drainage -line; that is, upon a river or stream, it is necessary to know both the -flood and low-water discharge of the stream. Frequently no reliable -data on this subject are available, and the engineer must then make -such a study of the whole situation as will enable him to estimate the -minimum and maximum flow with considerable accuracy. - -There are numerous factors entering into the solution of this first -problem, such as the shape and length of the catchment area, its -general elevation, the character of its surface, whether mountainous, -hilly or flat, barren or timbered. - -Good topographic maps, if available, furnish valuable data on these -subjects and it is to be regretted that only a comparatively small -portion of the United States has been thus mapped in detail. - -The results of stream measurements, if any have been made in the -catchment basin, are especially important: These are usually few in -the high areas, on account of their inaccessibility. The year 1902 -marked a notable beginning of such measurements in California. In many -parts of the arid region of the United States, the best storage-sites -are situated in the upper or higher portions of the drainage systems. -This is especially true of the streams on the Pacific Slope having -their source in the High Sierras. As regulators of stream-flow and for -power purposes such storage is peculiarly valuable, while storage for -irrigation and domestic uses may be located nearer the valleys and the -centers of population. - -Frequently the engineer is required to build his dam where no such -data are available. In such instances he should endeavor to secure -the establishment of rain gauges and make measurements of the flow of -the main stream and its principal tributaries at various places to -obtain the desired information. Even this may not suffice, owing to the -limited time at his disposal, and he must resort to the use of certain -empirical rules or formulas, and make such comparisons and deductions -from known conditions and results as will best answer his purpose. - -The engineer should know, approximately at least, the normal yield of -the catchment area, the duration of the minimum and maximum seasonal -flow, and the floods he may have to provide against during the -construction of his dam. These data are absolutely necessary to enable -him to provide ample wasteways for his reservoirs. Many of the failures -of earth dams have been the result of over-topping the embankment, -which would have been averted by an ample wasteway. The most notable -example of this kind in recent years was that of the South Fork Dam, at -Conemaugh, Pennsylvania, in 1889, resulting in what is generally known -as the “Johnstown Disaster.” - -There are several empirical rules and formulas for calculating the run -off from catchment areas and for determining the size of spillways -necessary to discharge this flow with safety to the dam. The proper -formula to apply in any given case, with the varying coefficients -of each, involves a thorough knowledge on the part of the designing -engineer of the principles upon which the different factors are based. - -It is unwise and often hazardous to make use of any important hydraulic -formula without knowing the history of its derivation. Experiments -are not always properly conducted, and often the deductions therefrom -are unreliable. A presentation and discussion of these formulas would -require more space than can be given in this study, and the technical -reader must therefore consult for himself, as occasion may require, the -various authorities cited. Formulas for the discharge or run-off from -catchment areas, as determined by Messrs. Craig, Dickens, Ryves and -others, are given by most writers on the subject of hydraulics. - - -Reservoir Basin. - -The next subject of inquiry relates to the reservoir basin. It is -necessary that its area and capacity at different depths should be -definitely known, and this information can only be obtained by having -the basin surveyed and contoured. A map should be made showing contours -at intervals of 2 to 10 ft., depending upon the size of the basin and -the use to which the reservoir is to be put. Reservoir basins have been -classified according to their location as follows: - - 1. Natural lakes. - - 2. Natural depressions on main drainage lines. - - 3. Natural depressions on lateral drainage lines. - - 4. Arbitrary and artificially constructed basins. - -Natural lakes may need to be investigated more or less thoroughly to -determine the character of their waters, whether saline, alkaline -or fresh. It may also be necessary to know their normal depth and -capacity, and to make a study of their outlet if they have one. In some -instances the storage capacity of a lake may be enormously increased by -means of a comparatively low and inexpensive embankment. - -The area of reservoir basin, mean depth, temperature of the water, -exposure of wind and sunshine, losses by seepage and evaporation, all -have a bearing upon the available water supply and influence the design -of the dam and accessories to the reservoir. - -In determining the character and suitability of materials for -constructing a dam it is necessary to make a careful study of the -soil and geological formation. This is best accomplished by digging -numerous test pits over the basin, especially in the vicinity of the -proposed dam site; borings alone should never be relied upon for this -information. For such an investigation the advisability of borrowing -material for dam construction from the reservoir basin is determined. -The porous character of the subsoil strata, or the dip and nature of -the bed rock, may forbid the removal of material from the floor of the -basin, even at a remote distance from the dam site. - -The area to be flooded should be cleared and grubbed more or less -thoroughly, depending again upon the use for which the water is -impounded. In no instance should timber be left standing below the -high-water level of the reservoir; and all rubbish liable to float and -obstruct the outlet tunnel and spillway during a time of flood should -be removed. - -The accessories to a reservoir, to which reference has been made, may -be enumerated as follows: - - 1. Outlet pipes or tunnel. - - 2. Gate tower, screens and controlling devices. - - 3. Sluiceways for silt or sand. - - 4. Wasteway channel or weir. - - 5. Cover, settling basin, aerating devices, etc. - -Some of these are necessary and common to all classes of reservoirs, -while others are employed only in special cases, as for domestic water -supplies. All reservoirs formed by earth embankments must have at least -two of these, namely a wasteway, which is its safety valve, and outlet -pipes or outlet tunnel. - -It may be stated that the proper location and construction of the -outlet for a reservoir are of vital importance, since either to -improper location or faulty construction may be traced most of the -failures of the past. It is almost impossible to prevent water under -high pressure from following along pipes and culverts when placed in an -earth dam. The pipes and culverts frequently leak, and failure ensues. -Failure may result from one or more of the following causes: - - 1. By improper design and placement of the puddle around the pipes. - - 2. By resting the pipes upon piers of masonry without continuous - longitudinal support. - - 3. By reason of subsidence in the cuts of the embankments and - at the core walls, due to the great weight at these points. - - 4. Leakage due to inherent defects, frost, deterioration, etc. - -Mr. Beardsmore, the eminent English engineer who built the Dale Dyke -embankment at Sheffield which failed in 1864, and who was afterwards -requested to study and report upon the great reservoirs in Yorkshire -and Lancashire, said, after examination and careful study of reservoir -embankment construction, that “in his opinion there were no conditions -requiring that a culvert or pipes should be carried through any portion -of the made bank.” The writer would go even further and say that the -only admissible outlet for a storage reservoir formed by a high earth -dam is some form of tunnel through the natural formation at a safe -distance from the embankment. - - -Dam Site. - -The third preliminary study (that relating to the dam site itself) will -be considered under three heads: - - 1. Location. - - 2. Physical features, materials, etc. - - 3. Foundation. - -LOCATION.–The location for a dam is generally determined by the use -which is to be made of it, or by the natural advantages for storage -which it may possess. If it be for water power it is very frequently -located upon the main stream at the point of greatest declivity. If for -storage it may be, as we have seen, at the head of a river system, on -one of its tributaries, or in a valley lower down. - -The type of dam which should be built at any particular locality -involves a thorough knowledge, not alone of the catchment area and -reservoir basin, but also accurate information regarding the geology of -the dam site itself. It would be very unwise to decide definitely upon -any particular type of dam without first obtaining such information. -Too frequently has this been done, causing great trouble and expense, -if not resulting in a total failure of the dam. - -The conditions favorable for an earth dam are usually unfavorable for a -masonry structure, and vice versa. Again, there may be local conditions -requiring some entirely different type. - -Dams situated upon the main drainage lines of large catchment areas are -usually built of stone or concrete masonry, and designed with large -sluiceways and spillways for the discharge both of silt and flood -waters. It need scarcely be remarked that, as a rule, such sites are -wholly unsuited to earthwork construction. It is said, however, that -“every rule has at least one exception,” and this may be true of those -relating to dam sites, as will appear later under the head of new -types. - -In a general way, the location of high earth dams is governed by the -configuration of the ground forming the storage basin. It may not be -possible, however, to decide upon the best available site without -careful preliminary surveys and examinations of the geological -formation. - -All earth dams must be provided with a wasteway, ample to discharge the -maximum flood tributary to the reservoir. Whatever type of wasteway be -adopted, no reliance should ever be put upon the outlet pipes for this -purpose. The outlet should only figure as a factor of safety for the -wasteway, insuring, as it were, the accuracy of the estimated flood -discharge. The safety of the dam demands that ample provision be made -for a volume of water in excess of normal flood discharge. This most -necessary adjunct of earth dams may be an open channel, cut through -the rim of the reservoir basin, discharging into a side ravine which -enters the main drainage way some distance below the dam. It may be -necessary and possible to pierce the rim by means of a tunnel where its -length would not prohibit such a design. Lastly, there may be no other -alternative than the construction of an overfall spillway, at one or -both ends of the embankment. This last method is the least desirable of -any and should be resorted to only when the others are impracticable; -even then, the volume of water, local topography, geology, and -constructive materials at hand must be favorable to such a design. If -they are not favorable it may be asked, “what then?” Simply do not -attempt to build an earth dam at this site. - -PHYSICAL FEATURES, MATERIALS, ETC.–An investigation of the location -and the physical features of the dam site should include a careful and -scientific examination of the materials in the vicinity, to determine -their suitability for use in construction. An earth embankment cannot -be built without earth, and an earth dam cannot be built with safety -without the right kind of earth material. - -Test pits judiciously distributed and situated at different elevations -will indicate whether there is a sufficient amount of suitable -material within a reasonable distance of the dam. The type of earth -dam best suited for any particular locality, and its estimated cost, -are thus seen to depend upon the data and information obtained by -these preliminary studies. Economical construction requires the use of -improved machinery and modern methods of handling materials, but far -more important even than these are the details of construction. - -FOUNDATION.–We may now assume that our preliminary studies relating to -the location and physical features of the dam site are satisfactory. -We must next investigate the foundation upon which the dam is to be -built. This investigation is sometimes wholly neglected or else done in -such a way as to be practically useless. To merely drive down iron rods -feeling for so-called bed rock, or to make only a few bore-holes with -an earth auger should in no instance be considered sufficient. Borings -may be found necessary at considerable depths below the surface and -in certain classes of material, but dug pits or shafts should always -be resorted to for moderate depths and whenever practicable. Only by -such means may the true character of the strata underlying the surface, -and the nature and condition of the bed rock, if it be reached, become -known. If a satisfactory stratum of impermeable material be found it is -necessary also to learn both its thickness and extent. It may prove to -be only a “pocket” of limited volume, or if found to extend entirely -across the depression lengthwise of the dam site it may “pinch out” -on lines transversely above or below. Shafts and borings made in the -reservoir basin and below the dam site will determine its extent in -this direction, knowledge of which is very important. - -Fig. 1, showing a longitudinal section of the site of the Yarrow Dam of -the Liverpool Water-Works, England, illustrates the necessity of such -investigation. A bore hole at station 2 + 00 met a large boulder which -at first was erroneously thought to be bed rock. The hole at station 3 -+ 50 met a stratum of clay which proved to be only a pocket. - -The relative elevation of the different strata and of the bed rock -formation, referred to one common datum, should always be determined. -These elevations will indicate both the dip and strike of the rock -formation and are necessary for estimating the quantities of material -to be excavated and removed, including estimates of cost. They furnish -information of value in determining the rate of percolation or -filtration through the different classes of material and the amount -of probable seepage, as will appear later. The cost of excavating, -draining and preparing the floor or foundation for a dam is often very -great, amounting to 20 or 30% of the total cost. - -Fig. 2 is a transverse section of the Yarrow Dam. This particular dam -has been selected as fairly representative of English practice and -of typical design. It is one of the most widely known earth dams in -existence. - -[Illustration: FIG. 1.–LONGITUDINAL SECTION OF YARROW DAM SITE.] - -[Illustration: FIG. 2.–CROSS-SECTION OF YARROW DAM.] - -At the Yarrow dam site it was necessary to go 97 ft. below the original -surface to obtain a satisfactory formation or one that was impermeable. -A central trench was excavated to bed rock, parallel to the axis of the -dam, and filled with clay puddle to form a water-tight connection with -the rock, and prevent the water in the reservoir from passing through -the porous materials under the body of the embankment. This interesting -dam will be more fully described later, when the different types of -earth dams are discussed. - - - - -CHAPTER III. - -_Outline Study of Soils. Puddle._ - - -The following study of soils is merely suggestive and is here given -to emphasize the importance of the subject, at the risk of being -considered a digression. Soil formations are made in one of three ways: - - 1. By decomposition of exposed rocks. - - 2. By transportation or sedimentation of fine and coarse - materials worn from rocks. - - 3. By transformation into humus of decayed organic matter. - -The transforming agencies by which soils succeed rocks in geological -progression have been classified as follows: - - 1. Changes of temperature. - - 2. Water. - - 3. Air. - - 4. Organic life. - -_Heat_ and its counter agent frost are the most powerful forces in -nature, their sensible physical effects being the expansion and -contraction of matter. - -_Water_ has two modes of action, physical and chemical. This agent is -the great destroyer of the important forces, cohesion and friction. -_Cohesion_ is a force uniting particles of matter and resists their -separation when the motion attempted is perpendicular to the plane of -contact. _Friction_ is a force resisting the separation of surfaces -when motion is attempted which produces sliding. The hydrostatic -pressure and resultant effect upon submerged surfaces need to be -kept constantly in mind. When the surface is impermeable the line of -pressure is normal to its plane, but when once saturated there are also -horizontal and vertical lines of pressure. Since the strength of an -earth dam depends upon two factors, namely, its weight and frictional -resistance to sliding, the effect of water upon different materials -entering into an earth structure should be most carefully considered. -This will therefore occupy a large place in these pages. An earth -embankment founded upon rock may become saturated by water forced up -into it from below through cracks and fissures, reducing its lower -stratum to a state of muddy sludge, on which the upper part, however -sound in itself, would slide. The best preliminary step to take in such -a case is to intersect the whole site with wide, dry, stone drains, -their depths varying according to the nature of the ground or rock. - -_Air_ contains two ingredients ever active in the process of -decomposition, carbonic acid and oxygen. - -_Organic Life_ accomplishes its decomposing effect both by physical -and chemical means. The effect of organic matter upon the mineral -ingredients of the soil may be stated as follows: - - 1. By their hydroscopic properties they keep the soil moist. - - 2. Their decomposition yields carbonic acid gas. - - 3. The acids produced disintegrate the mineral constituents, - reducing insoluble matter to soluble plant food. - - 4. Nitric acid results in _nitrates_, which are the most - valuable form of nutritive nitrogen, while ammonia and the - other salts that are formed are themselves direct food for - plants. - -_Vegetable Humus_ is not the end of decomposition of organic matter, -but an intermediate state of transformation. Decay is a process almost -identical with combustion, where the products are the same, and the end -is the formation of water and carbonic acid, with a residue of mineral -ash. The conditions essential to organic decomposition are also those -most favorable to combustion or oxidation, being (1) access of air, (2) -presence of moisture, and (3) application of heat. - -Now the coöperation of these chemical and physical forces, which are -ever active, is called “weathering.” Slate rock, for instance, weathers -to clay, being impregnated with particles of mica, quartz, chlorite and -hornblend. Shales also weather to clay, resulting often in a type of -earth which is little more than silicate of aluminum with iron oxide -and sand. - -In the vicinity of the Tabeaud Dam, recently built under the personal -supervision of the author, the construction of which will be described -later, there is to be found a species of potash mica, which in -decomposing yields a yellow clay (being ochre-colored from the presence -of iron), mixed with particles of undecomposed mica. This material -is subject to expansion, and by reason of its lack of grit and its -unctuous character it was rejected or used very sparingly. Analysis of -this material gave, Silica, 54.1 to 59.5%; potash, 1.5 to 2.3%; soda, -2.7 to 3.7%. - -Soil analysis may be either mechanical or chemical. For purposes of -earthwork, we are most interested in the former, having to deal with -the physical properties of matter. Chemical analysis, however, will -often afford information of great value regarding certain materials -entering into the construction of earth dams. The most important -physical properties are: - - (1) Weight and specific gravity. - - (2) Coefficient of friction and angle of repose. - - (3) Structure and coloring ingredients. - - (4) Behavior toward water. - -There are two distinct methods of mechanical analysis: (1) Granulating -with sieves, having round holes. (2) Elutriating with water, the -process being known as silt analysis. - -It would require a large volume to present the subject of soil analysis -in any way commensurate with its importance. Experiments bearing upon -the subjects of imbibition, permeability, capillarity, absorption and -evaporation, of different earth materials, are equally interesting and -important.[1] - -The permeability of soils will be discussed incidentally in connection -with certain infiltration experiments to be given later. - - -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. - -[Illustration: FIG. 3.–PLAN OF TABEAUD RESERVOIR, WITH CONTOURS.] - -[Illustration: FIG. 4.–PLAN OF TABEAUD DAM, SHOWING BED ROCK DRAINAGE -SYSTEM.] - -[Illustration: 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. - -[Illustration: 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. - -[Illustration: FIG. 7.–VIEW OF NORTH TRENCH, TABEAUD DAM.] - -[Illustration: FIG. 8.–VIEW OF SOUTH TRENCH, TABEAUD DAM.] - -[Illustration: 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. - -[Illustration: 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. - -[Illustration: 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. - -[Illustration] - -[Illustration: 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. - -[Illustration: 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. - - -Earth Dams with Puddle Core Wall or Face. - -YARROW DAM.–The Yarrow dam of the Liverpool Water-Works is a notable -example of the second type, (a section of which is shown in Fig. 2.) -An excavation 97 ft. in depth was made to bed rock through different -strata of varying thickness, and a trench 24 ft. wide was cut with -side slopes 1 on 1 for the first 10 ft. in depth below the surface. -The trench was then carried down through sand, gravel and boulders -with sides sloping 1 in 12. The upper surface of the shale bed rock -was found to be soft, seamy and water-bearing. Pumps were installed -to keep the water out of the trench while it was being cut 4 or 5 ft. -deeper into the shale. The lower portion was then walled up on either -side with brickwork 14 ins. in thickness, and the trench between the -walls was filled with concrete, made in the proportion of 1 of cement, -1 of sand and 2 of gravel or broken stone. By so doing a dry bed was -secured for the foundation of the puddle wall. Two lines of 6-in. pipes -were laid on the bed rock, outside of the walls, and pipes 9 ins. in -diameter extended vertically above the top of the brickwork some 27 -ft. These pipes were filled with concrete, after disconnecting the -pumps. After refilling the trench with puddle to the original surface, -a puddle wall was carried up simultaneous with the embankment, having a -decreasing batter of 1 in 12, which gave a width of 6 ft. at the top. -This form of construction is very common in England and Figs. 14 and 15 -show two California dams, the Pilarcitos and San Andres, of the same -general type. - -[Illustration: FIG. 14.–CROSS-SECTION OF PILARCITOS DAM.] - -[Illustration: FIG. 15.–CROSS-SECTION OF SAN ANDRES DAM.] - -ASHTI EMBANKMENT.–This is not a very high embankment, but being typical -of modern dams in British India, where the puddle is generally carried -only to the top of the original surface of the ground, and not up -through the body of the dam, it is thought worthy of mention. Fig. 16 -shows a section of this embankment, which is located in the Sholapur -District, India. - -The central portion of this dam above the puddle trench is made of -“selected black soil;” then on either side is placed “Brown Soil,” -finishing on the outer slopes with “Murum.” Trap rock decomposes first -into a friable stony material, known in India as “Murum” or “Murham.” -This material further decomposes into various argillaceous earths, the -most common being the “black cotton soil” mentioned above. - -[Illustration: FIG. 16.–CROSS-SECTION OF ASHTI TANK EMBANKMENT.] - -This particular dam has been adversely criticised on account of the -lack of uniformity in the character of the materials composing the -bank. It is claimed that the materials being of different density and -weight, unequal settlement will result, and lines of separation will -form between the different kinds of materials. - -Earth materials do not unite or combine with timber or masonry, but -there are no such distinct lines of transition and separation between -different earth materials themselves as Fig. 16 would seem to indicate. - - -Puddle Trench. - -In the last three dams mentioned (Figs. 14, 15, 16) the puddle -trenches are made with vertical sides or vertical steps and offsets. -A wedge-shaped trench certainly has many advantages over this form. -Puddle being plastic, consolidates as the dam settles, filling the -lowest parts by sliding on its bed. It thus has a tendency to break -away from the portion supported by the step, and a further tendency to -leave the vertical side, thus forming cracks and fissures for water to -enter. The argument advanced by those holding a different view, namely, -that it is difficult to dress the sides of a trench to a steep batter -and to timber it substantially, has in reality little weight when put -to practical test. Mr. F. P. Stearns, in describing the recent work -of excavating the cut-off trench of the North Dike of the Wachusett -reservoir, Boston, said it was found to be both better and cheaper -to excavate a trench with slopes than with vertical sides protected -by sheeting. He favored this shape in case of pile-work and for the -purpose also of wedging materials together. - -Mr. Wm. J. McAlpine’s “Specifications for Earth Dams,” representing the -best practice of 25 years ago, which are frequently cited, contain the -following description of how to prepare the up-stream floor of the dam: - - Remove the pervious and decaying matter by breaking up the natural - soil and by stepping up the sides of the ravine; also by several - toothed trenches across the bottom and up the sides. - -One of Mr. McAlpine’s well known axioms was, “water abhors an -angle.” The “stepping” and “toothed” trenches above specified need -not necessarily be made with vertical planes, but should be made by -means of inclined and horizontal planes. The writer’s experience and -observation leads him to think that all excavations in connection with -earth dams requiring a refill should be made wedge-shaped so that the -pressure of the superincumbent materials in settling will wedge the -material tighter and tighter together and fill every cavity. A paper -by Mr. Wm. L. Strange, C. E., on “Reservoirs with high Earthen Dams -in Western India,” published in the Proceedings of the Institution of -Civil Engineers, Vol. 132, (1898), is one of the best contributions to -the literature on this subject, known to the writer. Mr. Strange states -that - - the rate of filtration of a soil depends upon its porosity, - which governs the frictional resistance to flow, and the - slope and length of the filamentary channels along which the - water may be considered to pass. It is evident, therefore, - that the direct rate of infiltration in a homogeneous soil - must decrease from the top to the bottom of the puddle - trench. The best section for a puddle trench is thus a - wedge, such as an open excavation would give. It is true - that the uppermost infiltrating filaments when stopped by - the puddle, will endeavor to get under it, but a depth will - eventually be reached when the frictional resistance along - the natural passages will be greater than that due to the - transverse passage of the puddle trench, and it is when - this occurs that the latter may be stopped without danger, - as the _filtration to it_ will be less than that - _through_ it. This depth requires to be determined in - each case, but in fairly compact Indian soils 30 feet will - be a fair limit. - - -Puddle Wall vs. Puddle Trench. - -There is a diversity of opinion among engineers in regard to the proper -place for the puddle in dam construction. Theoretically, the inner -face would be preferable to the center, for the purpose of preventing -any water from penetrating the embankment. It is well known that all -materials immersed in water lose weight in proportion to the volume of -water they displace. If the upper half of the dam becomes saturated -it must neccesarily lose both weight and stability. Its full cohesive -strength can only be maintained by making it impervious in some way. -The strength of an earth dam depends upon three factors: - - 1. Weight. - 2. Frictional resistance against sliding. - 3. Cohesiveness of its materials. - -These can be known only so long as no water penetrates the body of -the dam. When once saturated the resultant line of pressure is no -longer normal to the inner slope, for the reason that there is now a -force tending to slide the dam horizontally and another due to the -hydrostatic head tending to lift it vertically. When the water slope -is impervious the horizontal thrust is sustained by the whole dam and -not by the lower half alone. When once a passage is made into the body -of the dam, the infiltration water will escape along the line of least -resistance, and if there be a fissure it may become a cavity and the -cavity a breach. - -For practical reasons, mainly on account of the difficulty of -maintaining a puddle face on the inner slope of a dam, which would -require a very flat slope, puddle is generally placed at the center as -a core wall. - -It was thought possible at the Tabeaud dam to counteract the tendency -of the face puddle to slough off into the reservoir by use of a broken -stone facing of riprap. This covering will protect the puddle from the -deteriorating effects of air and sun whenever the water is drawn low -and also resists the pressure at the inner toe of the dam. - - -Percolation and Infiltration. - -The earlier authorities on the subject of percolation and infiltration -of water are somewhat conflicting in their statements, if not confused -in their ideas. We are again impressed with the importance of a clearly -defined and definite use of terms. The temptation and tendency to use -language synonymously is very great, but it is unscientific and must -result in confusion of thought. Let it be observed that _filtration_ -is the process of mechanically separating and removing the undissolved -particles floating in a liquid. That _infiltration_ is the process -by which water (or other liquid) enters the interstices of porous -material. That _percolation_ is the action of a liquid passing through -small interstices; and, finally, that _seepage_ is the amount of fluid -which has percolated through porous materials. - -Many recent authorities are guilty of confusion in thought or -expression, as will appear from the following: - -One says, for instance, that a - - rock is water-tight when non-absorbent of water, but that a soil - is not water-tight unless it will absorb an enormous quantity of - water. - -This would seem to indicate that super-saturation and not pressure is -necessary to increase the water-tightness of earth materials. - -Again, in a recent discussion regarding the saturation and percolation -of water through the lower half of a reservoir embankment, it was -remarked, that - - the more compact the material of which the bank is built, - the steeper will be the slope of saturation. - -Exception was taken to this, and the statement made, that - - _with compact material_, the sectional area of flow - is larger below a given level with porous material, and as - the bank slope is one determining factor of the line of - saturation, this line tends to approach the slope line; - while with porous material in a down-stream bank, the slope - of saturation is steeper and the area of the flow less. - -In reply to this, it was said, - - that it is obvious that if the embankment below the core - wall is built of material so compact as to be impervious - to water, no water passing through the wall will enter it, - and the slope of saturation will be vertical. If it be - less compact, water will enter more or less according to - the head or pressure, and according to its compactness or - porosity, producing a slope of saturation whose inclination - is dependent on the frictional resistance encountered by - the water. And the bank will be tight whenever the slope of - saturation remains within the figure of the embankment. - -Further, - - that it was necessary to distinguish between the slope assumed - by water _retained in_ an embankment and that taken by water - _passing through_ an embankment made of material too porous to - retain it; where the rule is clearly reversed and where the more - porous the material the steeper the slope at which water will run - through it at a given rate. - -These citations are sufficient to emphasize the importance of exact -definition of terms and clear statement of principles. - -The latest experiments relating to the percolation of water through -earth materials and tests determining the stability of soils are -those made during the investigations at the New Croton Dam and -Jerome Park Reservoir, New York, and those relating to the North -Dike of the Wachusett Reservoir, Boston. These are very interesting -and instructive, and it is here proposed to discuss the results and -conclusions reached in these cases, after some introductory remarks -reciting the order of events. - -NEW CROTON DAM.–In June, 1901, the Board of Croton Aqueduct -Commissioners of New York requested a board of expert engineers, -consisting of Messrs. J. J. R. Croes, E. F. Smith and E. Sweet, to -examine the plans for the construction of the earth portion of the New -Croton Dam, and also the core wall and embankment of the Jerome Park -reservoir. - -This report was published in full in Engineering News for Nov. 28, -1901. It was followed in subsequent issues of the said journal by -supplemental and individual reports from each member of the board -of experts, and by articles from Messrs. A. Fteley, who originally -designed the works, A. Craven, formerly division engineer on this work, -and W. R. Hill, at that time chief engineer of the Croton Aqueduct -Commission. - -After describing the New Croton Dam, the board of experts preface their -remarks on the earth embankment by saying that - - it has been abundantly proven that up to a height of 60 - or 70 ft. an embankment founded on solid material and - constructed of well-selected earth, properly put in place, - is fully as durable and safe as a masonry wall and far less - costly. - -There are, in fact, no less than 22 earth dams in use to-day exceeding -90 ft. in height, and twice that number over 70 ft. in height. Five of -the former are in California, and several of these have been in use -over 25 years. The writer fails to appreciate the reason for limiting -the safe height of earth dams to 60 or 70 ft. - -The New Croton Dam was designed as a composite structure of masonry -and earth, crossing the Croton Valley at a point three miles from the -Hudson River. The earth portion was to join the masonry portion at a -point where the latter was 195 ft. high from the bed rock. The Board -thought there was no precedent for such a design and no necessity -for this form of construction. The point to be considered here was -whether a dam like this can be made sufficiently impermeable to water -to prevent the outer slope from becoming saturated and thus liable to -slide and be washed out. - -The design of the embankment portion was similar to all the earth dams -of the Croton Valley. In the center is built a wall of rubble masonry, -generally founded upon solid rock, and “intended to prevent the free -seepage of water, but not heavy enough to act alone as a retaining wall -for either water or earth.” - -Fig. 17 shows a section which is typical of most New England earth -dams; and Fig. 18, the sections of two of the Croton Valley dams, New -York water supply. These dams all have masonry core walls, illustrating -the third type of dams given on page 33. - -[Illustration: FIG. 17.–CROSS-SECTION OF A TYPICAL NEW ENGLAND DAM.] - -The board of experts made numerous tests by means of borings into -the Croton Valley dams to determine the slope of saturation. The -hydraulic laboratory of Cornell University also made tests of the -permeability of several samples of materials taken from pits. All the -materials examined were found to be permeable and when exposed to water -to disintegrate and assume a flat slope, the surface of which was -described as “slimy.” - -Pipe wells were driven at different places into the dams and the line -of saturation was determined by noting the elevations at which the -water stood in them. In all the dams the entire bank on the water side -of the core wall appeared to be completely saturated. Water was also -found to be standing in the embankment on the down-stream side of the -core wall. The extent of saturation of the outer bank varied greatly, -due to the difference in materials, the care taken in building them, -and their ages. Fig. 19 gives the average slopes of saturation as -determined by these borings. - -The experts stated - - that the slope of the surface of the saturation in the bank - is determined by the solidity of the embankment: The more - compact the material of which the bank is built, the steeper - will be the slope of saturation. - -As a result of their investigations, the experts were of the opinion -that the slope of saturation in the best embankments made of the -material found in the Croton Valley is about 35 ft. per 100 ft., and -that with materials less carefully selected and placed the slope may be -20 ft. per 100 ft. - -Further, that taking the loss of head in passing through the core wall, -and the slope assumed by the plane of saturation, the maximum safe -height of an earth dam with its top 20 ft. above water level in the -reservoir and its outside slope 2 on 1, is 63 to 102.5 ft. This is a -remarkable finding in view of the fact that the Titicus Dam, one of the -Croton Valley dams examined, has a maximum height above bed rock of 110 -ft. and has been in use seven years. This dam is not a fair example to -cite in proof of their conclusion, because its _effective head_ is only -about 46 ft.[2] - -[Illustration: BOG BROOK DAM.] - -[Illustration: MIDDLE BRANCH DAM. - -FIG. 18.–CROSS-SECTION OF TWO CROTON VALLEY DAMS, SHOWING SATURATION.] - -Mr. Fteley gave as a reason for the elevation of the water slope -found in the outer bank of the Croton dams the fact of their being -constructed of fine materials and stated that with comparatively porous -materials they would have shown steeper slopes of saturation. - -Mr. Craven argued that all dams will absorb more or less water, and -that porosity is merely a degree of compactness; that slope implies -motion in water, and that there is no absolute retention of water in -the outer bank of a dam having its base below the plane indicated by -the loss of head in passing through the inner bank and then through a -further obstruction of either masonry or puddle; that there is simply a -partial retention, with motion through the bank governed by the degree -of porosity of the material. - -Fig. 19 is a graphical interpretation of the conclusion reached by the -board of experts, as already given on page 41. “A” is an ideal profile -of a homogeneous dam with the inner slope 3 on 1 and the outer slope 2 -on 1. The top width is made 25 ft. for a dam having 90 ft. effective -head, the high-water surface in the reservoir being 10 ft. below the -crest of the dam. This ideal profile is a fair average of all the earth -dams of the world. Not having a core wall to augment the loss of head, -it fairly represents what might be expected of such a dam built of -Croton Valley material, compacted in the usual way. It should be noted -that the intersection of the plane of saturation with the rear slope of -the dam at such high elevation as shown indicates an excessive seepage -and a dangerously unstable condition. - - -Preliminary Study of Profile for Dam. - -The preliminary calculations for designing a profile for an earth dam -are simple and will here be illustrated by an example. Let us assume -the following values: - - a. Central height of dam, 100 ft. - - b. Maximum depth of water, 90 ft., with surface 10 ft. below - crest of dam. - - c. Effective head, 90 ft. - - d. Weight of water, 62.5 lbs. per cu. ft. - - e. Weight of material, 125 lbs. per cu. ft. - - f. Coefficient of friction, 1.00, or equal to the weight. - - g. Factor of safety against sliding, 10. - - The width corresponding to the vertical pressure of 1 ft. is, - (62.5 × 10)/125 = 5 ft. - -[Illustration] - -[Illustration: FIG. 19.–GRAPHICAL INTERPRETATION OF STUDIES OF BOARD OF -EXPERTS ON THE ORIGINAL EARTH PORTION OF THE NEW CROTON DAM.] - -The hydrostatic pressure per square foot at 90 ft. depth is, 62.5 × 90 -= 5,625 lbs. - -The dam, having a factor of safety of 10, must present a resistance of, -5,625 × 10 = 56,250 lbs., or 28 tons per square foot. - -The theoretical width of bank corresponding to 90 ft. head and a factor -of 10 is shown by the dotted triangle (A-B-B) to be 450 ft., (B, Fig. -19) with slopes 2½ on 1. - -To this must be added the width due to the height of crest above the -water surface in the reservoir and the width of crest. - -The former would be, 2 (2½ × 10) = 50 ft., and the latter by -Trautwine’s rule, 2 + 2√100 = 22 ft., giving a total base width of 522 -ft. - -Let us now assume that the slope of saturation may be 35 ft. per 100 -ft. We observe that this intersects the base 40 ft. within the outer -toe of the bank slope. If the plane of saturation was 33 ft. per 100, -it would just reach the outer toe. It would be advisable to enlarge -this section by adding a 10-ft. berm at the 50-ft. level, having a -slope not less than 3 on 1 for the up-stream face, and two 15-ft. berms -on the down-stream face, having slopes 2½ on 1. The additional width -of base due to these modifications in our profile amounts to 65 ft., -giving a total base width of 587 ft., and increasing the factor of -safety from 10 to 13. It should be remembered that if the bank becomes -saturated this factor of safety may be reduced 50%, the coefficient of -moist clay being 0.50. - -The loss of head due to a core wall of masonry, as designed for the -New Croton Dam, was assumed by the board of experts to be 21 ft., or -17% of the depth of water in full reservoir. It has been stated by -several authorities that the primary object of a masonry core wall is -to afford a water-tight cut-off to any water of percolation which may -reach it through the upper half of the embankment. It appears that -absolute water-tightness in the core wall is not obtained, although the -core walls of the Croton dams are said to be “the very best quality of -rubble masonry that can be made.” - -Mr. W. W. Follett, who is reported to have had considerable experience -in building earth dams, and who has made some valuable suggestions -thereupon, is emphatic in saying, - - that the junction of earth and masonry forms a weak point, that - either a puddle or masonry core in an earthen dam is an element - of weakness rather than strength. - -He also thinks the usual manner of segregating and depositing -materials different in density and weight, and thus subject to -different amounts of settlement, as bad a form of construction as could -be devised. - -Core walls may prevent “free passage of water” and “excessive seepage,” -but are nevertheless of doubtful expediency. - - -Earthwork Slips and Drainage. - -Mr. John Newman, in his admirable treatise on “Earthwork Slips and -Subsidences upon Public Works,” classifies and enumerates slips as -follows: - - Natural causes, 7. - Artificial causes, 31. - Additional causes due to impounded water, 7. - -After describing each cause he presents 39 different means used to -prevent such slips and describes methods of making repairs. - -Mr. Wm. L. Strange has had such a large and valuable experience and has -set forth so carefully and lucidly both the principles and practice of -earth dam construction, that the writer takes pleasure in again quoting -him on the subject of _drainage_, of which he is an ardent advocate. He -says that, - - thorough drainage of the base of a dam is a matter of vital - necessity, for notwithstanding all precautions, some water will - certainly pass through the puddle. - -It is at the junction of the dam with the ground that the maximum -amount of leakage may be expected. The percolating water should be -gotten out as quickly as possible. The whole method of dealing with -slips may be summed up in one word–_drainage_. - -The proper presentation of these two phases of our subject would in -itself require a volume. The interested reader is therefore referred to -the different authorities and writers cited in Appendix II. - - -Jerome Park Reservoir Embankments. - -The Jerome Park reservoir is an artificial basin involving the -excavation and removal of large quantities of soil, and the erection of -long embankments with masonry core walls, partly founded on rock and -partly on sand. The plan and specifications call for an embankment 20 -ft. wide on top, with both slopes 2 on 1, and provide for lining the -inner slope with brick or stone laid in concrete, and for covering the -bottom with concrete laid on good earth compacted by rolling. - -[Illustration: Section at Sta. 99.] - -[Illustration: Section at Sta. 76+20. - -FIG. 20.–GRAPHICAL EXHIBIT OF STUDIES OF JEROME PARK RESERVOIR -EMBANKMENT.] - -Wherever bed rock was not considered too deep below the surface the -core walls were built upon it. In other places the foundation was -placed 8 to 10 ft. below the bottom of the reservoir and rested upon -the sand. - -It appears that the plans of the Jerome Park embankment were changed -from their original design, prior to the report of the board of -experts, on account of two alleged defects, namely, “cracks in the core -wall” and “foundation of quicksand,” and incidentally on account of the -supposed instability of the inner bank. - -In describing the materials on which these embankments rest the experts -remarked - - that all these fine sands are unstable when mechanically - agitated in an excess of water, and that they all settle in - a firm and compact mass under the water when the agitation - ceases. That they are quite unlike the true quicksands whose - particles are of impalpable fineness and which are “quick” - or unstable under water. - -Fig. 20 is a graphic exhibit of the results of tests made at “Station -76 + 20,” and at “Station 99,” to determine the flow line of water in -the sand strata underlying the embankment and bottom of the Jerome Park -reservoir. - -The experts reported that there was no possible danger of sliding or -sloughing of the bank; that the utmost that could be expected would -be the percolation of a small amount of water through the embankment -and the earth; and that this would be carried off by the sewers in the -adjacent avenues; that a large expenditure to prevent such seepage -would not be warranted nor advisable. - -In concluding their report, however, they recommended changing the -inner slope of 2 on 1 to 2½ on 1, and doubling the thickness of the -concrete lining at the foot of the slope to preclude all possibility -of the sliding or the slipping of the inner bank in case of the water -being lowered rapidly in the reservoir. - -Mr. W. R. Hill, then chief engineer of the Croton Aqueduct Commission, -favored extending the core walls to solid rock. He took exception to -the manner of obtaining samples of sand by means of pipe and force-jet -of water, claiming that only the coarsest sand was obtained for -examination. He did not consider fine sand through which three men -could run a ¾-in. rod 19 and 20 ft. to rock without use of a hammer, -very stable material upon which to build a wall. - - -North Dike of the Wachusett Reservoir, Boston. - -The North Dike of the Wachusett Reservoir is another large public work -in progress at the present time. It is of somewhat unusual design -and the preliminary investigations and experiments which led to its -adoption are interesting in the extreme.[3] - -The area to be explored in determining the best location for the dike -was great, and the preliminary investigations conducted by means of -wash drill borings, very extensive. A total of 1,131 borings were made -to an average depth of 83 ft., the maximum depth being 286 ft. The -materials were classified largely by the appearance of the samples, -though chemical and filtration tests were also made. The plane of the -ground water was from 35 to 50 ft. below the surface, and the action of -the water-jet indicated in a measure the degree of permeability of the -strata. - -In addition to these tests experimental dikes of different materials, -and deposited in different ways, were made in a wooden tank 6 ft. wide, -8 ft. high and 60 ft. long. The stability of soils when in contact with -water was experimented with, as shown in Fig. 21, in the following -manner: - -An embankment (Fig. 21) was constructed in the tank of the material to -be experimented with, 2 ft. wide on top, 6 ft. high, with slopes 2 on -1, and water admitted on both sides to a depth of 5 ft. The top was -covered with 4-in. planks 2 ft. long and pressure applied by means of -two jack screws resting upon a cross beam on top of the planks. - -With a pressure of three tons per square foot, the 4-in. planks were -forced down into the embankment a little more than 6 ins., resulting -in a very slight bulging of the slopes a little below the water level. -Immediately under the planks the soil became hard and compact. A man’s -weight pushed a sharp steel rod, ¾-in. in diameter, only 6 to 8 ins. -into the embankment where the pressure was applied, while outside of -this area the rod was easily pushed to the bottom of the tank. - -These results corroborate in a general way the practical experience of -the author, both in compressed embankments, where he found it necessary -to use a pick vigorously to loosen the material of which they were -composed, and in embankments made by merely dumping the material from -a track, in which case the earth is so slightly compressed that an -excavation is easily made with a shovel. - -[Illustration: Fig. 21.] - -[Illustration: Fig. 22.] - -[Illustration: Fig. 23.–CAN FOR DETERMINING FRICTIONAL RESISTANCE] - -[Illustration: Fig. 24.] - -[Illustration: Fig. 25. - -FIGS. 21 TO 24.–EXPERIMENTAL DIKES AND CYLINDER EMPLOYED IN STUDIES FOR -THE NORTH DIKE OF THE WACHUSETT RESERVOIR; AND (FIG. 25) CROSS-SECTION -OF THE DIKE.] - -The difference in the coefficient of friction of the same material -when dry and when wet greatly modifies the form of slope. The harder -and looser the particles, the _straighter_ will be the slope line in -excavation and slips. The greater the cohesion of the earth, the _more -curved_ will be the slope, assuming a parabolic curve near the top–the -true form of equilibrium. - -RATE OF FILTRATION.–The rate of filtration through different soils was -experimented with by forming a dike in the tank previously mentioned, -as shown in Fig. 22. - -The dike was made full 8 ft. high, 7 ft. wide on top, with a slope on -the up-stream side of 2 on 1, and on the down-stream side 4 on 1. This -gave a base width of 55 ft. Immediately over the top of the dike there -was placed 3 ft. of soil to slightly consolidate the top of the bank -and permit the filling of the tank to the top without overflowing the -dike. The water pressure in different parts of the dike was determined -by placing horizontal pipes through the soil crosswise of the tank. -These pipes were perforated and covered with wire gauze, being -connected to vertical glass tubes at their ends. The end of the slope -on the down-stream side terminated in a box having perforated sides and -filled with gravel, thus enabling the water to percolate and filter out -of the bank without carrying the soil with it. - -When the soil was shoveled loosely into the tank, without consolidation -of any kind, it settled on becoming saturated and became quite compact. -It took five days for the water to appear in the sixth gauge pipe near -the lower end of the tank. After the pressure, which was maintained -constant, had been on for several weeks, the seepage amounted to one -gallon in 22 minutes. When the soil was deposited by shoveling into the -water, the seepage amounted to one gallon in 34 minutes. - -The relative filtering capacities of soils and sands were thought to -be better determined by the use of galvanized iron cylinders of known -areas. - -Fig. 23 shows one of the cylinders. These latter experiments confirmed -those previously made at Lawrence, by Mr. Allen Hazen, for the -Massachusetts State Board of Health. They showed that the loss of head -was directly proportioned to the quantity of water filtered and that -the quantity filtered will vary as the square of the diameter of the -_effective size_ of the grains of the filtering material.[4] - -The material classed as “permeable” at the North Dike of the Wachusett -Reservoir has an effective diameter of about 0.20 mm. A few results are -given in the following table: - - -Amount of Filtration in Gallons per Day, Through an Area of 10,000 Sq. -Ft., With a Loss of Head or Slope of 1 ft. in 10 ft. - - Material. Unit ratios. U. S. gallons. - - (1) Soil 1 510 - (2) Very fine sand 14 7,200 - (3) Fine sand 176 90,000 - (4) Medium sand 784 400,000 - (5) Coarse sand 4,353 2,200,000 - -To be sure that the accumulation of air in the small interstices of -the _soil_ was not the cause of the greatly reduced filtration through -it, another series of experiments was conducted in the wooden tank, as -shown in Fig. 24. - -A pair of screens was placed near each end of the tank, filled with -porous material, sand and gravel, and the 50-ft. space between filled -with soil. The soil was rammed in 3-in. layers, and special care taken -to prevent water from following along the sides and bottom of the tank. -One end was filled with water to near the top, while the other end gave -a free outlet. - -After this experiment had been continued for more than a month, the -amount of seepage averaged 1.7 gallons per 24 hours, or about 32 drops -per minute. - -Filtration tests were also made through soil under 150 ft. head, or 5 -lbs. per sq. in., with results not materially different, it is stated, -from those already given. The soil used in all these tests contained -from 4 to 8% by weight of organic matter. This was burned and similar -tests made with the incinerated soil, resulting in an increase of about -20% more seepage water. - -PERMANENCE OF SOILS.–This last material experimented with suggests the -subject of _permanence_ of soils. This was reported upon separately and -independently by Mr. Allen Hazen and Prof. W. O. Crosby. These experts -agreed in their conclusion, stating - - that the process of oxidation below the line of saturation would be - extremely slow, requiring many thousands of years for the complete - removal of all the organic matter, and that the tightness of the - bank would not be materially affected by any changes which are - likely to occur. - -It has been remarked, - - that of all the materials used in the construction of - dams, _earth_ is physically the least destructible of - any. The other materials are all subject to more or less - disintegration, or change in one form or another, and in - earth they reach their ultimate and most lasting form. - -In speaking of the North Dike of the Wachusett Reservoir, Mr. Stearns -remarked that, - - it was evident by the application of Mr. Hazen’s formula for - the flow of water through sands and gravels, that the very - fine sands found at a considerable depth below the surface - would not permit enough water to pass through them if a dike - of great width were constructed, to cause a serious loss of - water, and it was also found that the soil, which contained - not only the fine particles or organic matter, but also a - very considerable amount of fine comminuted particles, which - the geologist has termed “rock flour,” would be sufficiently - impermeable to be used as a substitute for clay puddle. - -Fig. 25 shows the maximum section of the North Dike with its cut-off -trench. The quantities and estimated cost of the completed structure -are given in the table herewith: - - |––– Cost –––| - Per cent. - Work. Quantities. Unit Actual. total. - (cu. yds.) Price. - Soil 5,250,000 $0.05 $262,500 34.7 - Cut-off trench 542,000 .20 108,400 19.3 - Borrowed - earth and gravel 200,000 .20 40,000 - Slope paving 50,000 2.20 110,000 14.6 - Sheet-piling, - pumping, etc. 117,000 15.5 - Engineering and - preliminary investigations 120,000 15.9 - ––––––– ––––– - Total cost $757,900 100.0 - - -Druid Lake Dam, Baltimore, Md. - -Another very interesting and instructive example of high earth dam -construction is that of the Druid Lake Reservoir embankment, Baltimore, -Md. - -This dam was built under the supervision of Mr. Robt. K. Martin. -Construction was begun in 1864, and the dam was finished in 1870. Mr. -Alfred M. Quick, present chief engineer of the water-works of the -City of Baltimore has given a very lucid description of this work in -Engineering News of Feb. 20, 1902. - -Fig. 26 is a cross-section of this dam, showing the method of -construction so clearly as to scarcely need further description. The -banks D-D on either side of the central puddle wall were carried up in -6-in. layers with horses and carts, and kept about 2 ft. higher than -the puddle trench, which always contained water. The banks E-E were -made of dumped material, after which the basins F-F were first filled -with water and finally filled by dumping material into the water from -tracks being moved in toward the center. - -[Illustration: FIG. 26–WORKING CROSS-SECTION OF DRUID LAKE DAM.] - -After reaching the top of this fill, banks B-B-B were built up in -layers similar to D-D. The second set of basins C-C were then filled -in a manner similar to F-F. The remaining portion A-A was constructed -in layers like D-D and B-B, with the addition of compacting each layer -with a heavy roller. - -Finally the inner face slope was carried up in 3-in. layers and -thoroughly rolled, after which 2 ft. of “good puddle” was put upon the -inner slope the latter was rip-rapped, the crown covered with gravel -and the rear slope sodded. - -Some years after completion, a driveway was built along the outer -slope, as shown, which had a tendency to strengthen the dam, though not -designed expressly for that purpose. - -It is of interest to know that the influent, effluent and drain pipes -were originally constructed through or under the embankment. These -pipes were laid upon solid earth, and where they passed through the -puddle wall were supported upon stone piers 6 ft. apart. As might be -expected, they soon cracked badly and were finally abandoned, new ones -being placed in the original ground at the south side of the lake. Mr. -Quick states that so far as is known there has never been any evidence -of a leak through the embankment during these 32 years of service. - - -New Types of Dams; Bohio, Panama Canal. - -A brief description will now be given of three different dams designed -for Bohio, on the proposed Panama Canal. Mr. George S. Morison’s paper -before the American Society of Civil Engineers, on “The Bohio Dam,” -and the discussion thereon, especially that by Mr. F. P. Stearns, were -quite fully reported in Engineering News for March 13 and May 8, 1902. -In constructing the Panama Canal it will be necessary to impound the -waters of the Chagres River, near Bohio, to maintain the summit level -of this canal and supply water for lockage. - -THE FRENCH DESIGN.–Fig. 27 is an enlarged section of the original -design of the new French Co. This design has no core wall, but at -the up-stream toe a concrete wall was to be built across the river -between the two lines of sheet-piling. At the down-stream toe a large -amount of riprap was to be placed to prevent destruction of the dam -during construction. In this case it would be necessary to construct -a temporary dam above and also to use the excavation for the locks -as a flood spillway. This method would involve considerable risk to -the work, on account of the large volume of flood waters it might be -necessary to take care of during construction. - -ISTHMIAN CANAL COMMISSION.–The dam proposed by the Isthmian Canal -Commission is shown by Fig. 28. This was designed to be an absolutely -water-tight closure of the geological valley, by using a masonry core -wall carried down to bed rock. The maximum depth being 129 ft., it was -planned to rest the concrete wall on a series of pneumatic caissons -reaching to rock. The spaces between the caissons would be closed and -made water-tight. Both slopes of the earth embankment were to have -horizontal benches and be revetted with loose rock. - -MR. MORISON’S DESIGN.–To appreciate fully the object and aim of the -third design, Fig. 29, which may be called a new type, although similar -in many respects to the North Dike of the Wachusett reservoir already -illustrated and described, it should be stated that the equalized flow -of the Chagres River is put at 1,000 cu. ft. per sec. Of this quantity -it is estimated that 500 cu. ft. would be needed for lockage and 200 -cu. ft. for evaporation. This leaves 300 cu. ft. per sec. available for -seepage and other losses or to be wasted. - -[Illustration] - -[Illustration] - -[Illustration: FIGS. 27 TO 29.–DESIGNS FOR THE BOHIO DAM, PANAMA -CANAL.] - -It will thus be seen that a scarcity of water is not in this instance -a condition demanding an absolutely water-tight dam. The amount of -seepage permissible without endangering the stability of the structure -is the real point now to be discussed. - -The third design, which was proposed by Mr. Morison, is shown by Fig. -29. The topography and configuration of this dam site is not unlike -that of the San Leandro Dam, California, soon to be described, while -the general design is similar, as has been remarked, to the North Dike -of the Wachusett Reservoir. - -This third design contemplates a compound structure, formed by two -rock-fill dams situated about 2,120 ft. apart, with the intervening -space filled with loose rock, earth and other available material. -Immediately below the upper and higher rock-fill dam, it is proposed -to place across the canyon a puddle wall 50 ft. in width, resting over -two lines of sheet-piling 30 ft. apart. This piling would probably not -reach farther than 50 ft. below tidewater, the solid rock floor being -about 100 ft. deeper. - -Mr. Morison made use of Mr. Hazen’s filtration formula for estimating -the rate and quantity of seepage through the permeable strata below the -dam. This formula is: - - h t + 10° - V = cd² –– –––––– - l 60 - - where - - V = rate of flow in meters per day through the whole section. - c = constant varying from 450 to 1,200, - according to cleanness of the sand. - d = “effective size” of sand in mm. - h = head in feet. - l = length or distance water must pass. - t = temperature of the water (Fahr.) - -This formula should be used only when the _effective sizes_ of sands -are from 0.10 to 3.0 mm. and with _uniformity coefficients_ below -5.0[5]. - -Mr. Morison used the following values: c = 1,000; d = 1.0 mm.; h = 90 -ft.; l = 2,500 ft.; t = 90°; for the solution of this problem, and -obtained a velocity of 0.002 ft. per sec. The bed of sand and gravel -was assumed to have a sectional area of 20,000 sq. ft. for 2,500 ft. in -length. This gives a seepage of 40 cu. ft. per sec. - -It is believed that the above rate of 0.002 ft. per sec., equivalent to -1⅜ ins. per minute, or 7 ft. per hour, is not sufficient to move any of -the material. The velocity of water percolating through sand is found -to vary directly as the head and inversely as the distance. - -The value of “c” in the formula is larger for sands of filters -favorable for flow, and smaller for compacted materials and dams. - -Mr. Morison thought it might be nearer the actual conditions to assume -d = 0.50 mm.; c = 500; and l = 5,000 ft.; in which case the seepage -would only amount to 2.5 ft. per sec. In this last assumption the -“effective size” of sand grains is 2½ times that classed as “permeable -material” at the North Dike of the Wachusett Reservoir. - -Prof. Philipp Forchheimer, of Gratz, Austria, recommends the use of the -formula, - - h - ––– = a√ + b√² - l - -for the percolation through soils between loam and loamy sand. -Sellheim, Masoni, Smreker, Kröber and other authorities on filtration -use still other formulas, to which the reader and student is referred -for further research. - -The writer, having had occasion in his professional practice to study -quite carefully the subject of ground waters, and their percolation -or flow through different classes of materials and under varying -conditions, is of the opinion that rarely does the cross-section of -a stream-channel, filled with sand, gravel and debris, present, even -approximately, a homogeneous or uniform mass; and that there are, -almost without exception, strata of material much coarser and more -porous than the general average. In other words, that it is extremely -difficult to arrive at a uniformity coefficient. It is unwise to place -much reliance upon an estimated flow where this is the case. The -formula may be used with confidence where the layers are artificially -made, and where there is no uncertainty regarding the uniform character -of the material. In most natural channels there are distinct lines -of flow, and under considerable hydrostatic head or pressure these -lines of flow would surely enlarge. There is a wide difference between -permissible and dangerously excessive percolation through an earth -embankment. The local features, economical considerations and magnitude -of the risks, all bear upon this question and must be considered for -each particular case. - -It is of interest to compare the estimated cost of the three designs -proposed for the Bohio Dam, based upon the same unit prices, as follows: - - French Engineers’ design $3,500,000 - Isthmian Canal Commissioners’ design 8,000,000 - Mr. Morison’s design 2,500,000 - -No comments will be made upon these figures, further than to remark -that the successful building of a stable dam, accomplished by the use -of an excessive quantity of materials and at a cost beyond reasonable -requirements, is mainly instructive as illustrating “how not to do it.” -It is creditable to execute substantial works at a reasonable cost, -but it reflects no credit upon any one to construct them regardless of -expense. - - -Combined Rock-fill and Earth Dam. - -Fig. 30 shows a section of the Upper Pecos River Dam near Eddy, N. M. - -This dam is quite fully described by Mr. Jas. D. Schuyler, in his -recent book on “Reservoirs for Irrigation, Water-Power and Domestic -Water-Supply,” and need not be mentioned in this paper, further than -to call attention to the combination of rock-fill and earth which -constitutes its particular type of construction. This type of dam is -believed to be for many localities a very good one, but up to the -present time has only been adopted for dams of moderate height, under -60 ft. - - -The San Leandro Dam, California. - -A section of the San Leandro Dam, near Oakland, Cal., is shown by -Fig. 31. This section was supplied by Mr. W. F. Boardman, hydraulic -engineer, who superintended the construction of the dam, from his own -private notes and data. It differs materially from sections heretofore -published, and is 5 ft. higher, thus making it rank as the highest -earth dam in the world of which we have an authentic record. - -The dam was commenced in 1874, and brought up to a height of 115 ft. -above the bed of the creek in 1898. At the present time it is 500 ft. -in length on the crest and 28 ft. wide. The original width of the -ravine at the base of the dam was 66 ft. The present width of base -from toe to toe of slopes is 1,700 ft. The height of embankment above -the original surface is 125 ft., with a puddle trench extending 30 ft. -below. - -[Illustration: FIG. 30.–CROSS-SECTION OF UPPER PECOS RIVER DAM; -COMBINED ROCK FILL AND EARTH.] - -[Illustration: FIG. 31.–DEVELOPED SECTION OF SAN LEANDRO DAM.] - -All that portion of the dam within a slope of 2½ on 1 at the rear and -3 on 1 at the face is built of choice material, carefully selected and -put in with great care. The portion outside of the 2½ on 1 slope line -at the down-stream side of the dam, was _sluice in_ from the adjacent -hills regardless of its character, and is composed of ordinary soil -containing more or less rock. - -This process of sluicing was carried on during the rainy season, when -there was an abundance of water, and it was intended to be continued -until the canyon below the dam had been filled to an average slope of -6.7 on 1 at the rear of the dam. It was thought that the location was -particularly favorable for this kind of construction, the original -intention being to raise the dam from time to time, not only to -increase the storage as the demand for water increased, but to meet -the annual loss in capacity caused by the silting up of the reservoir -basin. The latter has amounted to about 1 ft. in depth per annum. - -METHOD OF CONSTRUCTION.–Under the main body of the dam, the surface was -stripped of all sediment, sand, gravel and vegetable matter. Choice -material, carefully selected, was then brought by carts and wagons and -evenly distributed over the surface in layers about 1 ft. or less in -thickness. This was sprinkled with just enough water to make it pack -well, not enough to make it like mud. During construction a band of -horses was led by a boy on horseback over the entire work, to compact -the materials and assist in making the dam one homogeneous mass. No -rollers were used on this dam. - -The central trench was cut 30 ft. below the original bed of the creek. -In the bottom of this trench three secondary trenches, 3 ft. wide by 3 -ft. deep, were made and filled with concrete. These concrete walls were -carried up 2 ft. above the general floor of the trench, to break the -continuity of its surface. - -The original wasteway, constructed at the north end of the dam, has -been practically abandoned, having been substituted by a tunnel of -larger capacity. The original wasteway was excavated in the bed rock -of the natural hillside, and although lined with masonry, is not in -the best condition. The author considers its location an objectionable -feature, as menacing the safety of the dam, and thinks it should be -permanently closed. - -A wasteway tunnel, 1,487 ft. in length, was constructed in 1888, -through a ridge extending north of the dam. This has a sectional area -of about 10×10 ft., lined with brick masonry throughout, having a grade -of 2½%. - -The criticism might be made of the tunnel that it is faulty in design -at the entry or reservoir end, where the water must first fall over -a high spillway wall, aerating the water before entering the tunnel -proper. The water even then has not easy access to the tunnel, and no -adequate arrangements have been made for ventilation, so as to insure -the utilization of its maximum capacity. The maximum depth of water in -the reservoir is about 85 ft., and the full capacity 689,000,000 cu. -ft. of water. The catchment area is 43 square miles, and the surface -of the reservoir when full 436 acres. The outlet pipes are placed in -two tunnels at different elevations through the ridge north of the dam. -There are no culverts or pipes extending through the body of the dam -itself. - - -Hydraulic-fill Dams. - -No discussion of earth dams would be complete without some reference -being made to the novel type of construction developed in western -America in recent years, by which railroad embankments and water-tight -dams are built up by the sole agency of water. The water for this -purpose is usually delivered under high pressure, as it is generally -convenient to make it first perform the work of loosening the earth -and rock in the borrow pit, as well as subsequently to transport them -to the embankment, and there to sort and deposit them and finally part -company with them after compacting them solidly in place, even more -firmly than if compressed by heavy rollers. Sometimes, however, water -is delivered to the borrow pit without pressure, in which event the -materials must be loosened by the plow or by pick and shovel by the -process called ground sluicing in placer mining parlance. - -An abundance of water delivered by gravity under high pressure is -usually regarded as one of the essential factors in hydraulic-fill dam -building, but it is not essential that there be a large continuous -flow. The Lake Frances Dam, recently constructed for the Bay Counties -Co., of California, by J. D. Schuyler, is 75 ft. high, 1,340 ft. long -on top, and contains 280,000 cu. yds. The dam was built up by materials -sluiced by water that was forced by a centrifugal pump through a 12-in. -pipe and 3-in. nozzle, against a high bank, whence the materials were -torn and conveyed by the water through flumes and pipes to the dam. -About 6 cu. ft. per sec. of water was thus used, and at one stage of -the work the supply stream was reduced to less than 0.1 ft. per sec., -the water being gathered in a pond and pumped over and over again. - -The chapter on hydraulic-fill dams in Mr. Schuyler’s book on -“Reservoirs for Irrigation” will be found to contain matter on the -subject interesting to those who desire to pursue it further, and the -reader is again referred to that work. - - -An Impervious Diaphragm in Earth Dams. - -As a result of the recent extended discussion concerning the design -of the New Croton Dam and the Jerome Park Reservoir embankments, -the Engineering News of Feb. 20, 1902, contained a very suggestive -editorial entitled, “Concerning the Design of Earth Dams and Reservoir -Embankments.” The opinion is given that no type of structure that man -builds to confine water can compare in permanence with earth dams, -after which the following pertinent questions are asked: - - 1. How shall an earth dam be made water-tight? - - 2. What is the office and purpose of the masonry core wall? - - 3. Would not a water-proof diaphragm of some kind be better - than a core wall of either masonry or puddle? - -The article then suggests a number of designs of diaphragm construction, -with a special view of obtaining absolute water-tightness, by use of -asphaltum, cement mortar, steel plates, etc. Special emphasis was put -upon the _principle_ of constructing a water-proof diaphragm. The -matter of relative cost is advanced as an argument in favor of the -diaphragm principle as against the usual orthodox method. The saving in -cost is to be accomplished by the use of inferior materials and less -care in the handling of them, or by both. It is suggested that almost -any kind of material available, rock, sand or gravel, will answer -every purpose where good earth is not to be found. Further, that this -material may be dumped from the carts, cars or cableways, or be placed -by the hydraulic-fill method. - -The writer believes the diaphragm method of construction may have some -merits, but that it is attended by the very great risk of neglecting -principles most vitally important to the successful construction of -high earth dams, which will now be formulated and advanced, as follows: - - - - -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.” - -*** END OF THE PROJECT GUTENBERG EBOOK EARTH DAMS, A STUDY *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. Special rules, set forth in the General Terms of Use part -of this license, apply to copying and distributing Project -Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm -concept and trademark. 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