Friday, July 1, 2011

The Standard Proctor Test

The Standard Proctor Test is a test developed by the American Society for Testing and Materials (ASTM). The test, which can be referred to as the 'laboratory compaction test', is performed on a soil sample to determine the soil's optimum moisture content (OMC) and maximum compaction density. The maximum compaction density is also known as the maximum dry unit weight.

The apparatus consists of a two-piece cylinder and baseplate, and a 'hammer' that is dropped on the soil in the cylinder to compact it. The soil is dried in an oven and then weighed. The weight of the soil is used to determine the amount of water to add for the test. If you had a 1.0kg dry soil sample, and you were testing for 10% moisture, then you would add 100g of water to the sample. Typically, the same soil type is tested with multiple moisture contents to determine which one provides the highest level of compaction.

The information obtained by doing this test is used in the field by comparing the moisture content in the soil to the test values to determine if the soil is near the desired compaction level and, typically, the maximum value is desired.

To see videos of the Standard Proctor Test in action, click here for Part 1, Part 2, Part 3, Part 4.

  • soil is compacted in a standard mold using a standard hammer dropped from a standard distance
  • Standard Proctor uses a 5.5lb hammer dropped from 12". Modified Proctor uses a 10lb hammer dropped from 18"
  • take four samples, dry them in the oven
  • add varying water contents to the samples making sure the water contents bracket the OMC
  • compact each sample in the mold using specified numbers of blows per layer
  • determine the wet unit weight of the sample
  • dry in oven and determine water content
  • find the dry unit weight
  • plot moisture vs. dry unit weight
  • peak of the curve gives OMC and maximum compaction density

Will soil that is overly wet or overly dry compact well?

How many samples are normally tested during a Standard Proctor Test?

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