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.