Published: Jan 2011
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DURING THE INSTALLATION OF A TYPICAL EARTH-fill project, the density, water content, and degree of compaction of the earth fill is confirmed and documented by testing the in-place compacted soil. The compacted soil is measured to determine its dry density and water content. These values are then compared with the maximum dry density (standard reference density) and optimum water content of the soil being evaluated. The project specifications usually require the in-place dry density to be a minimum percentage of the maximum dry density. The specifications will usually require the placement water content of the fill to be within a range of water content relative to the optimum water content of the soil being tested. The in-place density and water content of compacted soils are measured in the field using various methods. Several methods are also used to determine the laboratory reference values for maximum dry density and optimum water content to which the field measurements are compared. Specifications should state which methods are acceptable for measuring the field density and water content as well as which method(s) is (are) acceptable for determining the reference values for the soil. The ratio of the in-place field density test to the standard reference density test for that soil is called “the percent compaction.” Compute percent compaction by dividing the in-place dry density by the maximum dry density of the standard reference density test, then multiply by 100 and express as a percentage. The maximum dry density determined by the standard reference density test must be determined for the same soil or a previously tested sample of the same soil type that represents the soil where the in-place test was made. Refer to Section F of this chapter for guidelines on selecting the proper standard reference density used as a comparison for in-place tests. The computed degree of compaction and in-place water content should be reported to the nearest whole number because the tests are not accurate enough to state results to any higher precision. For example, the specifications may indicate that compaction shall be to 95 % (not 95.0 %) of the maximum dry density determined by ASTM D698. The specifications may also indicate that the water content shall be from 2 % (not 2.0 %) below to 2 % above the optimum water content determined by ASTM D698. An example of reporting the measured degree of compaction is to state the measurement as 96 % compaction, not 95.6 %. In reporting measured water content, the result would be stated as 1 % wet of optimum, not 1.2 %.