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<br />EM 1110-2-1913 <br />31 Mar 78 <br /> <br />for the collected seepage as shown in figures 5-9b and 5-9c. <br /> <br />5-11. Design of Drainage Layers. The design of pervious toe drains and <br />horizontal and inclined drainage layers must ensure that such drains <br />have adequate thickness and permeability to transmit seepage without any <br />appreciable head loss while at the same time preventing migration of <br />finer soil particles. The design of drainage layers must satisfy the <br />criteria outlined in Appendix E for filter design. Horizontal drainage <br />layers should have a mintmum thickness of 18 in. for construction <br />purposes. <br /> <br />5-12. Compaction of Drainage Layers. Placement and compaction of <br />drainage layers must ensure that adequate density is attained, but <br />should not allow segregation and contamination to occur. Vibratory <br />rollers are probably the best tYl'e of equipment for compaction of <br />cohesionless material although crawler tractors and rubber-tired rollers <br />have also been used successfully. Saturation or flooding of the mate- <br />rial as the roller passes over it will aid in the compaction process and <br />in some cases has been the only way specified densities could be <br />attained. Loading, dumping, and spreading operations should be observed <br />to ensure that segregation does not occur. Gradation tests should be <br />run both before and after compaction to ensure that the material meets <br />specifications and does not contain too many fines. <br /> <br />5-14 <br /> <br />. <br /> <br />~ <br /> <br />~ <br /> <br />e <br /> <br />. <br /> <br />" <br /> <br />e <br />