15 AUGUST 2005
obtained with a particular compaction effort. A standard five-point compaction curve relating
density and water content can be developed by the procedures outlined in ASTM D 1557.
The impact compaction test results normally constitute the basis on which field
compaction control criteria are developed for inclusion in the specifications. However, for
some cohesionless soils, higher densities can be obtained by the vibratory compaction method
(commonly referred to as maximum relative density), described in EM 1110-21906. The
required field compaction is generally specified as a percentage of laboratory maximum dry
density and referred to as percent ASTM D 1557 maximum density. Water content is an
important controlling factor in obtaining proper compaction. The required percentage of
maximum dry density and the compaction water content should be selected on the basis of the
engineering characteristics, such as compression moduli, settlement, and shear strength,
desired in the compacted backfill. It should be noted that these characteristics could be
adversely affected by subsequent increases in water content after placement. This situation
could result from an increase in the groundwater level after construction.
Density control of placed backfill in the field can be facilitated by the use of rapid
compaction check tests (ASTM D 5080). A direct rapid test is the one-point impact compaction
test. Rapid indirect tests, such as the Proctor needle penetration for cohesive soils or the cone
resistance load for cohesionless soils, can also be used when correlations with ASTM D 1557
maximum density have been established.