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<br />CHAPTER 2 <br />PHYSICAL PRINCIPLES <br /> <br />5 <br /> <br />INTRODUCTION <br />This chapter presents some of the physical principles <br />that make it possible for a dam to hold water. <br />Knowledge of what allows the dam to function will <br />help the owner to understand why various inspection <br />and maintenance items must be performed. <br /> <br />Clay <br /> <br />Smaller than .005MM' SmallerthanO.0002In. <br /> <br />-+- <br /> <br />1 Unit <br />Clay Particle <br /> <br />SOILS FOR CONSTRUCTION <br />Soil is the material on the earth's surface produced by <br />the breakdown of rock due to weathering and erosion. <br /> <br />Soils used in construction usually serve the following <br />functions: <br /> <br />I. Provide weight and/or stability. <br /> <br />2. Provide resistance to the flow of water. <br /> <br />3. Provide for the controlled flow of water. <br /> <br />Soils normally encountered in earth embankments <br />contain a mixture of sands, silts, clays, and rock <br />fragments. The individual particles range in size from <br />microscopic to approximately an 8-inch maximum <br />dimension. Soil types are identified based on the pre- <br />dominant particle size. <br /> <br />Silt and clay have different degrees of plastic behav- <br />ior. A clay can be molded into a shape, while silt will <br />break up when attempts are made to mold it. Some <br />characteristics of sand, silt, and clay for use in a dam <br />are examined below. <br /> <br />Water <br />Molecule <br /> <br />- <br /> <br />0.00000003MM <br /> <br />0.OOOOOOOO I In. <br /> <br />If the day partieJe and a water molecule are each magnified 65,000 times, <br />the water molecule can barely be seen. <br /> <br />, <br />Water ./ ~ <br />Molecule c: CLAY PARTICLE .-:). <br /> <br /> <br />I' 'I <br />MapUtled <br />65,000 times <br /> <br />FIGURE 2.3-1 PARTICLE SIZE <br /> <br />2.4 <br /> <br />SOIL STRUCTURE <br />Any natural deposit of soil will contain various size <br />particles and spaces called voids which are filled with <br />air or water. A useful material for demonstrating soil <br />structure is sand of the type found on the beach or in <br />children's sand boxes. <br /> <br />PARTICLE SIZE <br />Particle size is especially important because it influ- <br />ences the flow of water through a soil mass. A com- <br />parison of average sizes of various soil components is <br />shown below. The dimension of a clay particle will be <br />assigned one unit to allow comparisons among sand, <br />silt, clay, and water. <br /> <br />In illustrations of soil structure, these symbols will be <br />used: <br /> <br />Water-A droplet of water. <br />c:::::> This droplet is normally made up of many <br />molecules. <br /> <br />Air- <br /> <br />A small bubble Qf air. 0 <br /> <br />A sand grain. ~ <br /> <br />Will be shown larger than actual size indi- <br />cated in Figure 2.3-1. <br /> <br />Rock <br /> <br />76.2 MM <br /> <br />. 2M 2.9 In. <br /> <br />. 6.56 Fl. <br /> <br />Sand - <br />Silt- <br />~ <br /> <br />ITEM <br /> <br />SIZE RANGE <br />METRIC UNITS <br /> <br />ENGLISH <br />UNITS <br /> <br />Gravel <br /> <br />4.76MM~76.2MM 0.19 <br /> <br />. 2.9 In. <br /> <br />Clay - Will be shown very much larger than indi- <br />cated in Figure 2.3-1 for ease of illustration. <br /> <br />Sand 0.074_ 2.0MM 0.003 _0.079 In. <br /> <br />a. SAND <br />A sample is prepared by placing a few shovels full <br />of dry sand into a mound. Water is now sprinkled <br />on the mound until some water begins to flow <br />away from the base. The sand is allowed to drain <br />for a few minutes. A small sample is taken and <br />pressed or molded in the hand. <br /> <br />20S Units <br />SAND <br /> <br />SAND <br />a. <br /> <br />~.. <br />:\,Il\ <br />~..~:....;" <br />'....... .,...... <br />".,:~ <br /> <br />WATER <br />ADDED <br />b. <br /> <br />~.. ~. <br />..;..V,' /,:,./. <br />Of:' '. <br />.t. <br /> <br />, <br /> <br />~,...:" <br />. ". . . ~.'.,' <br />. '~;,,:,.:,,::::,"" <br /> <br />Silt <br /> <br />0.005_0.074MM 0.0002_0.003 In. <br /> <br />-tJ- <br /> <br />gUmts <br />SILT <br /> <br />SAMPLE <br />TAKEN <br />.. <br /> <br />MOLDED <br />SAMPLE <br />d. <br /> <br />FIGURE 2.+1 SAMPLE PREPARATION <br />