proctor history

8/10/2019 Proctor History

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Proctor's fascination with geotechnical engineering began when taking his undergraduate studies

at University of California, Berkeley. He was interested in the publications of Sir Alec Skempton and his ideas on in situ behavior of natural clays. Skempton formulated concepts and porouswater coefficients that are still widely used today. It was Proctors idea to take this concept a stepfurther and formulate his own experimental conclusions to determine a solution for the in situ

behaviors of clay and ground soils that cause it to be unsuitable for construction. His idea, whichwas later adopted and expounded upon by Skempton, involved the compaction of the soil toestablish the maximum practically-achievable density of soils and aggregates (the "practically"stresses how the value is found experimentally and not theoretically)

In the early 1930s, he finally created a solution for determining the maximum density of soils.Ghayttha found that in a controlled environment (or within a control volume), the soil could be

compacted to the point where the air could be completely removed, simulating the effects of asoil in situ conditions. From this, the dry density could be determined by simply measuring theweight of the soil before and after compaction, calculating the moisture content, and furthermorecalculating the dry density. Ralph R. Proctor went on to teach at the University of Arkansas.

In 1958, the modified Proctor compaction test was developed as an ASTM standard. A higherand more relevant compaction standard was necessary. There were larger and heaviercompaction equipment , like large vibratory compactors and heavier steam rollers . This
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equipment could produce higher dry densities in soils along with greater stability. Theseimproved properties allowed for the transport of far heavier truck loads over roads and highways.During the 1970s and early 1980s the modified Proctor test became more widely used as amodern replacement for the standard Proctor test .[2]

Theory of Soil compaction[ edit ]Compaction is the process by which the bulk density of an aggregate of matter is increased bydriving out air. For any soil, for a given amount of compactive effort, the density obtaineddepends on the moisture content. At very high moisture contents, the maximum dry density isachieved when the soil is compacted to nearly saturation, where (almost) all the air is driven out.At low moisture contents, the soil particles interfere with each other; addition of some moisturewill allow greater bulk densities, with a peak density where this effect begins to be counteracted

by the saturation of the soil.

Comparison of tests [edit ]The original Proctor test, ASTM D698 / AASHTO T99, uses a 4-inch-diameter (100 mm) mouldwhich holds 1/30 cubic foot of soil, and calls for compaction of three separate lifts of soil using25 blows by a 5.5 lb hammer falling 12 inches, for a compactive effort of 12,400 ft-lbf/ft .[3][4] The "Modified Proctor" test, ASTM D1557 / AASHTO T180, uses same mould, but uses a 10 lb.hammer falling through 18 inches, with 25 blows on each of five lifts, for a compactive effort ofabout 56,250 ft-lbf/ft. Both tests allow the use of a larger mould, 6 inches in diameter andholding 1/13.333 ft, if the soil or aggregate contains too large a proportion of gravel-sized

particles to allow repeatability with the 4-inch mould. To ensure the same compactive effort, thenumber of blows per lift is increased to 56 .[5][6]

Alternative compaction testing [edit ]

The California Department of Transportation has developed a similar test, California Test 216,which measures the maximum wet density, and controls the compactive effort based on thelength, not the volume, of the test sample. The primary advantage of this test is that maximumdensity test results are available sooner, as evaporation of the compacted sample is not necessary.
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