Compaction Tests (“Maximum Density” or “Proctor”)

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Course Synopsis:

This course material consists of an Engineer Manual as issued by the U.S. Army Corps of Engineers. The quiz author is J. Cloyce Darnell, P.E.

Soil Compaction Tests are frequently called "Maximum Density" or "Proctor" tests, with their names interchangeable. Specifications typically call for a Standard Proctor or a Modified Proctor, and usually specify a test method designation such as ASTM D698, for example. Sometimes both are used, varying with the design requirements. Standard Proctors provide less compactive effort than Modified Proctors. Modified Proctor tests of the same soil will yield a higher maximum density and lower optimum moisture content.

Proctor tests are performed in the laboratory to determine the maximum density, in dry pounds per cubic foot, of the tested soil and its corresponding optimum moisture that is practically achievable in the field. Field in-place density tests are then performed and compared to the "Proctor" maximum density to determine the percentage of the proctor. For example, if the Maximum Density/Proctor dry density is 130.0 pcf and the field density test is 125.5 dry pcf, the in-place "% of proctor" is 125.5/130.0 = 96.5%. Typically, project specifications require the soil to be compacted to some percentage, usually 95% -100% of a Standard or Modified Proctor.

This course explains the purpose, equipment, procedures, and result determination methods of the Corps of Engineer's Compaction Tests methods. Almost identical, with a few exceptions, are the ASTM D698 and AASHTO T-99 "Standard" Proctor methods. Additionally, the ASTM D1557 and AASHTO T-180 are "Modified" Proctor methods. Various agencies' specifications normally contain requirements citing either the Corps, ASTM, or AASHTO maximum density Proctor methods. Engineers should be familiar with all of these methods.

It is imperative that the specified test method be performed, and that it is performed in strict accord with the specified, published test method. Otherwise, the results may be deemed invalid, at potentially significant cost to the company or agency performing the tests. There is essentially no room for mistaken test methods or procedures. Shortcuts are not acceptable.

Course Objectives:

This course teaches the following specific knowledge and skills regarding Compaction Tests ("Maximum Density" or "Proctor"):

• Differing Types of Compaction Tests and Procedures Depending on Soil Gradation Results

• Required Equipment, Soil Sample Size, and Sample Preparation Procedures

• Compaction, Weighing, Drying, and Calculation Procedures

• Recording, Plotting, and Determining the Maximum Density and Optimum Moisture 

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