How to Calculate a Soil Compaction Curve

Weighing the Sample

• 1

  Weigh the tare on the scale. Add the sample of soil to be measured to the tare and be sure to subtract the weight of the tare if your scale does not have a function for it.

• 2

  Determine the total weight of the sample of compacted soil. This will be necessary to determine wet and dry volume.

• 3

  Dry the sample by putting it in the microwave and re-weighing the sample until a constant weight is achieved (indicating that the moisture has been removed) or in a standard oven at about 220 degrees Fahrenheit until constant weight is achieved.

• 4

  Determine the dry weight of the sample once constant weight is achieved. Subtract that value from the weight of the sample prior to drying. This is the weight of the water content that was in the soil.

• 5

  Add water in small increments to the dry sample and weigh with each addition of water. Do this until the weight of the sample starts to decrease due to the soil being displaced by water. This value is the "Optimum water content."

• 6

  Create a graph with the dry unit weight on the ordinate axis and the water content on the abscissa axis. Plot all of the weights of the sample starting with dry weight to the point where the weight began to decrease due to water displacement. The resulting graph represents the soil compaction curve.