Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 6—Filter Zones6.8 Specifications and density quality control and quality assurance for filtersand drainsContract specifications contain requirements for compacting sand for filters. Qualitycontrol personnel are responsible for ensuring that the specifications are met.Quality assurance personnel then ensure that the quality control methods andequipment are satisfactory.Filters are compacted using two principal types of specifications. Compaction ofsands is important for filter construction. Controlled compaction of the filter sandsis important to prevent settlement of the sands on wetting and liquefaction duringseismic activity. At the same time, filters should not be overly compacted becausethat can reduce their ability to “self-heal” or adjust to any movements in theunderlying embankment and foundation. The two types of specifications used forcontrolling compaction of sands and gravels are:• Method placement specification.—A method placement specification requires thefilter sand to be compacted in lifts of a stated maximum thickness usingspecified equipment operated in a specified manner. The specification assumesthat the designer has previous favorable experience with a specified method andfeels sure that the filter sand will have adequate properties, if it is compactedusing these procedures. This type of specification does not require a specificdensity or water content, but relies on the specified procedure to producedesirable filter.Quality control and quality assurance for this type of specification concentrateon observations and documentation of the processes used to place the filter,compared to the acceptable methods listed in the specifications.An example of a method placement specification is shown in the NRCS’sDrainfill, National Engineering Handbook, Part 642, Specification No. 24(2001f, p. 24-2). Class I compaction requires each layer of drainfill to becompacted “. . . by a minimum of two passes over the entire surface with asteel-drum vibrating roller weighing at least 5 tons and exerting a verticalvibrating force of not less than 20,000 pounds at a minimum frequency of1,200 times per minute, or by an approved equivalent method.”For filters, using smaller compaction equipment, such as walk-behind vibratoryrollers and plate compactors, may be required if working space is limited.Test fills can be performed in advance of construction to check on theadequacy of method type placements.151