Figure 13-2.—Data sheet for soil compaction test.material, you remove the collar and weigh the mold andcompacted material. Then take moisture contentsamples from the top and bottom of the specimen anddetermine the moisture content for each. If the twomoisture contents differ, use the average betweenthem.A modification of the above procedure uses a 51/2-pound tamper and the material is placed in threeequal layers, rather than five; otherwise, the test is thesame. The procedures can be found in ASTM D 698.Data and CalculationsFigure 13-2 shows the test results and calculationsfor a compaction test. As you can see, this test used a10-pound tamper and Proctor mold. Five runs weremade. After compaction, the weight of the compactedsoil and mold was recorded for each run. From this, theweight of the mold was subtracted to get the weight ofthe soil for each run. Then the wet unit weight wascomputed using the formula shown.Lines A, B, C, D, and E contain the data for themoisture-content test for each run. Note that for eachrun, there were two tests: one from the top of the moldand the other of soil from the bottom. The averageswere set down beside average moisture content.Finally, the dry unit weight (density) in pounds percubic foot (pcf) for each run was calculated by theformula shown. As you can see, for the samecompactive effort, the density varied with the averagemoisture content.The ultimate objective of the compaction test is todetermine the OMC; that is, the moisture content thatyields maximum density for a given compactive effort.13-3
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