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<br />e <br /> <br />. <br /> <br />i <br /> <br />e <br /> <br />. <br /> <br />. <br /> <br />e <br /> <br />RIVERSIDE <br /> <br />:EM 1110-2-1913 <br />31 Mar 78 <br /> <br />'" <br /> <br /> <br />LANDSIDE <br /> <br />:':":'-:::;':':.:'~:'::':,:,:~:'::..:.:...:..::~'~ <br /> <br />a. Horizontal drainage layer <br /> <br />R1VERSIDt <br /> <br /> <br />LANDSIOE <br /> <br />b. Inclined drainage layer-homogeneous embankment <br /> <br />RIVERSIDE <br /> <br /> <br />LAN051DE <br /> <br />c. Inclined drainage layer-zoned embankment <br /> <br />Figure 5-9. Use of horizontal and inclined drainage layers <br />to control seepage through an embankment <br /> <br />seepage and is used extensively in earth dams. It is rarely used in <br />levee construction because of the added cost, but might be justified <br />for short levee reaches in important locations where lands ide slopes <br />must be steep and other control measures are not considered adequate and <br />the levee will have high water against it for prolonged periods. The <br />effect of an inclined' drainage layer is to completely intercept embank- <br />ment seepage regardless of the degree of stratification in the embank- <br />ment or the material type riverward or landward of the drain. As a <br />matter of fact, the use of this type of drain allows the landside por- <br />tion of a levee to be built of any material of adequate strength regard- <br />less of permeability. When used between an impervious core and outer <br />pervious shell (fig. 5-9c), it also serves as a filter to prevent migra- <br />tion of impervious fines into the outer shell. If the difference in <br />gradation between the impervious and pervious material is great, the <br />drain may have to be designed as a graded filter (Appendix E). Inclined <br />drains must be tied into horizontal drainage layers to provide an exit <br /> <br />5-13 <br />