Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsConstruction specifications typically also include other requirements. Examplesfrom the NRCS’s Drainfill, National Engineering Handbook, Part 642,Specification No. 24 (2001f, p. 24-1) include:Drainfill shall be placed uniformly in layers not to exceed 12 inches thick beforecompaction. When compaction is accomplished by manually controlledequipment, the layers shall not exceed 8 inches thick. The material shall beplaced to avoid segregation of particle sizes and to ensure the continuity andintegrity of all zones. No foreign material shall be allowed to becomeintermixed with or otherwise contaminate the drainfill.Traffic shall not be permitted to cross over drains at random. Equipmentcross-overs shall be maintained, and the number and location of such crossoversshall be established and approved before the beginning of drainfill placement.Each crossover shall be cleaned of all contaminating material and shall beinspected and approved by the engineer before the placement of additionaldrainfill material.Any damage to the foundation surface or the trench sides or bottom occurringduring placement of drainfill shall be repaired before drainfill placement iscontinued.The upper surface of drainfill constructed concurrently with adjacent zones ofearthfill shall be maintained at a minimum elevation of 1 foot above the uppersurface of adjacent earthfill.When placed, drainfill shall be in a wet or near saturated condition. Each layerof drainfill shall be saturated immediately prior to compaction.Drainfill shall be placed in such a manner as to prevent segregation of particlesizes.Application of water in front of the vibratory roller drum during compaction iscrucial. The inability to achieve the desired density is typically due toinsufficient water application.• End result specification.—An end result specification requires the filter sand to becompacted to a specified value of dry density. Usually, the required density isspecified by reference to a standard test. The traditional method for specifyingfilter sand compaction uses relative density terminology and tests. ASTMD 4254 describes the test used to measure the minimum index density of a filtersand; ASTM D 4253 describes the test for maximum index density of a sand.NRCS’s Drainfill, National Engineering Handbook, Part 642, SpecificationNo. 24 (2001f, p. 24-2) shows an example of an end result specification. ClassA compaction requires each layer of drainfill to be compacted “. . . to a relativedensity of not less than 70 percent as determined by ASTM D 4254.”152