Figure 15-24.-Mixing a sample weighing 25 to 100 pounds.Figure 15-25.-Quartering a small sample.corners of the canvas and pulling over the samplesas if preparing to fold the canvas diagonally, asshown in figure 15-24. Then flatten and quarterthe sample.Samples Weighing Less Than25 PoundsFor samples of this size, place the sample onthe canvas or a clean sheet of paper. Mix itthoroughly with a trowel, form it into a conicalshape, and then flatten it with the trowel. Usingthe trowel, divide the sample into quarters, anddiscard two diagonally opposite quarters, asshown in figure 15-25. Remix the remainingmaterial, and repeat the process until the sampleis the size needed for the test.SOIL TESTINGIn soil testing, the Navy follows procedureslaid down by the American Society for TestingMaterials (ASTM). Generally speaking, a com-plete soil test proceeds according to the followingsteps:1. Determine the moisture content of repre-sentative samples. (This is preceded, of course,by the extraction of representative samples.)2. Perform a mechanical analysis of thesample to determine the sizes of soil particles (orgrains) and the distribution of sizes; this meansthe percentage of each size contained in the wholemass.3. Determine the specific gravity of represen-tative samples. The specific gravity of a substanceis expressed in terms of the ratio of the weightof a given volume of the substance to the weightof an equal volume of water. A cubic foot ofwater weighs 62.43 lb.For soil, determine the absolute specific grav-ity; by this we mean determine the ratio of theweight of a dense volume (volume exclusive of airspaces) to the weight of an equal volume of water.A cubic foot of dry sand, for example, weighsabout 100 lb. With air exhausted, however, acubic foot of sand weighs about 165.44 lb.Therefore, the specific gravity of sand equals165.44 divided by 62.43, or about 2.65.4. If the soil is clay or a similar fine-grainedsoil, determine the Atterberg limits. Over a cer-tain range of moisture content, a fine-grained soilremains plastic. A reduction below the bottom ofthe range causes the soil to become semisolid; anincrease above the range causes it to become fluid.The upper moisture content is called the liquidlimit; the lower is called the plastic limit.5. Compaction testing is used to determine themoisture-density relationships; or, in other words,to determine what moisture content results inmaximum compaction for a given compactive15-17
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