Lesson 4/Learning Event 3
Empty the water from the apparatus.
Repeat the second through the sixth steps, at least two or more times.
Compute the volume of the apparatus by averaging the measured weights, converting the average
to pounds (divide by 453.6 g/lb), and converting the average weight in pounds to volume (divide
by 62.4 pounds per cubic foot). The result is the volume in cubic feet. Note the example of the
computation in Figures 29 and 30.
Sand Calibration.
The Bulk Density of Sand is Affected by Changes in Temperature and
Humidity.
Sand calibration must be checked prior to each test. Use a container of known volume, such as the
Proctor mold. The mold with base plate attached is weighed empty. Attach the collar and place the
sand cone with the valve open on top. Pour the sand from about the same height that it will fall in a
field-dug hole and allow it to fall at its own rate into the mold. When the sand stops running into the
mold, close the valve on the cone. Carefully remove the sand cone and the mold collar using a straight
edge. Strike off the excess sand remaining on top of the mold. Brush off any sand adhering to the
outside of the mold. Weigh the mold, full of sand. Repeat the entire process and average the two
weights (mold full of sand). Subtract the weight of the empty mold from the average of the full weights.
The difference in weights divided by the known volume of the container is equal to the density of the
sand.
Surface Calibration
One more calibration must be made prior to starting the test. However, it is performed after the surface
is prepared and the template tray is in place.
Test Procedure
Setting the Template. Prior to the test, take a soil sample directly from the ground. The ground surface
where the density is to be determined is prepared by clearing and leveling. No attempt should be made
to smooth the surface with a spatula, trowel, or other tool. Place the template tray shown in Figure 18
flush on the surface. Seal any spaces on the inside edge under the plate with modeling clay. Force nails
through the holes in the tray to hold it firmly in position.
Surface Calibration. As mentioned above, the surface irregularities inside of the metal tray must be
accounted for. To do this, check the volume of the space between the inner surface of the upper cone
and the test surface.
Use the apparatus with its sand fill for this calibration.
With the valve closed, turn the apparatus over, large cone down, and place it over the hole in the
metal tray. Be careful not to jar or shake the container and cause packing of the sand.
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