From the preceding discussion, you know that compaction testing is performed to determine the OMC and the maximum density that can be obtained for a given soil at a given compactive effort. You also know that, using the maximum density, you can determine a range of densities and moisture contents that will satisfy the compaction requirements for a project. During the construction of that project, however, a control must be in place to measure whether or not the compaction requirements have been met. That control is density testing. If the results of the density test determine that the compaction process has produced a density within the range specified, then the compaction is complete. On the other hand, if the test results reflect densities that are

 Several different methods are used to determine the in-place density of a soil; however, the methods that EAs are most apt to use are the sand-displacement method and the nuclear moisture-density meter method.

A full discussion of the procedures used in the sand-displacement method can be found in Test Method for Pavement Subgrade, Subbase, and Base-Course Material, MIL-STD-621A, and in NAVFAC MO-330. This method, often called the sand-cone method, may be used for both fine-grained and coarse-grained materials. In general, the test consists of digging out a sample of the material to be tested, using calibrated sand to determine the volume of the hole from which the sample was removed and to determine the dry unit weight of the sample.

EQUIPMENT AND TOOLS. The essential equipment and tools that you will need to perform the test are shown in figure 13-4. In addition to these, you

Figure 13-5.Sample data sheet, calibration of sand-cone density apparatus.

will also need a baking pan, moisture content canisters, a paintbrush with moderately long bristles, and some modeling clay.

CALIBRATION. The sand-displacement method includes three calibration procedures that must be completed before you conduct the test. The first of the calibration procedures is the apparatus calibration that determines the volume of the jar and connecting cone (up through the cone valve).

To perform the calibration, you first weigh the assembled apparatus (jar and cone) when it is empty, clean, and dry. Record this weight on a data sheet similar to figure 13-5. Then you weigh the apparatus when the jar and the smaller end of the cone is filled with water (making sure that no air is entrapped in the water). Record this weight on the data sheet and then empty the water from the apparatus. After repeating these steps at least three times, you can then determine the average weight of the water and compute the volume of the apparatus, using the formulas shown in figure 13-5. The second calibration that you must make before performing the sand-cone test is sand calibration. The sand that you use in the sand-cone test must be clean, dry, and free-flowing with a constant moisture be in the sand. This sand is usually purchased in bulk quantities that can be used for many sand-cone tests performed over extended lengths of time. The density of the sand may be determined soon after the sand is received; however, since the bulk density of the sand is affected by changes in temperature and humidity, you must recalibrate the sand before each test.

Figure 13-6A.Data sheet (DD Form 1215) for in-place soil density, sand-cone method.

An alternate method of sand calibration uses a container of known weight, such as a Proctor mold. In this method, you first weigh the mold and the attached base plate. Then, after attaching the mold collar, you pour the sand through the sand cone into the mold. Next, you remove the collar, strike off the excess sand, brush off the outside of the mold and base plate, and weigh the sand-filled mold (with the base plate attached). The difference in weights (filled and empty) divided by the known volume of the mold is equal to the density of the sand.

The third calibration (surface calibration) is discussed as part of the site preparation since it must be performed at the test site.