Proctor compaction test
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The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given
soil Soil, also commonly referred to as earth or dirt Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debri ...
type will become most dense and achieve its maximum dry
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
. The test is named in honor of , who in 1933 showed that the dry density of a soil for a given compactive effort depends on the amount of water the soil contains during soil compaction. His original test is most commonly referred to as the standard Proctor compaction test; his test was later updated to create the modified Proctor compaction test. These laboratory tests generally consist of compacting soil at known moisture content into a cylindrical mold with a collar of standard dimensions of height and diameter using a compactive effort of controlled magnitude. The soil is usually compacted into the mold to a certain amount of equal layers, each receiving a number of blows from a standard weighted hammer at a specified height. This process is then repeated for various moisture contents and the dry densities are determined for each. The graphical relationship of the dry density to moisture content is then plotted to establish the compaction curve. The maximum dry density is finally obtained from the peak point of the compaction curve and its corresponding moisture content, also known as the optimal moisture content. The testing described is generally consistent with the
American Society for Testing and Materials ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
(ASTM) standards, and are similar to the
American Association of State Highway and Transportation Officials The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway design and construction throughout the United ...
(AASHTO) standards. Currently, the procedures and equipment details for the standard Proctor compaction test is designated by ASTM D698 and AASHTO T99. Also, the modified Proctor compaction test is designated by ASTM D1557 and AASHTO T180-D.


History

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 Sir Alec Westley Skempton (4 June 1914 – 9 August 2001) was an English civil engineer internationally recognised, along with Karl Terzaghi, as one of the founding fathers of the engineering discipline of soil mechanics. He established the soi ...
and his ideas on in situ behavior of natural clays. Skempton formulated concepts and porous water coefficients that are still widely used today. It was Proctor's idea to take this concept a step further 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, which was later adopted and expounded upon by Skempton, involved the compaction of the soil to establish 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 a soil in situ conditions. From this, the dry density could be determined by simply measuring the weight of the soil before and after compaction, calculating the moisture content, and furthermore calculating 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 higher and more relevant compaction standard was necessary. There were larger and heavier compaction equipment, like large vibratory compactors and heavier steel-face rollers. This equipment could produce higher dry densities in soils along with greater stability. These improved 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 a modern replacement for the standard Proctor test.


Theory of soil compaction

Compaction can be generally defined as the densification of soil by the removal of air and rearrangement of soil particles through the addition of mechanical energy. The energy exerted by compaction forces the soil to fill available voids, and the additional frictional forces between the soil particles improves the mechanical properties of the soil. Because a wide range of particles are needed in order to fill all available voids, well-graded soils tend to compact better than poorly graded soils. The degree of compaction of a soil can be measured by its dry unit weight, ''γd''. When water is added to the soil, it functions as a softening agent on the soil particles, causing them to slide between one another more easily. At first, the dry unit weight after compaction increases as the moisture content (''ω'') increases, but after the optimum moisture content (''ωopt'') percentage is exceeded, any added water will result in a reduction in dry unit weight because the pore water pressure (pressure of water in-between each soil particle) will be pushing the soil particles apart, decreasing the friction between them.


Comparison of tests

The original Proctor test, ASTM D698 / AASHTO T99, uses a mould which holds 1/30 cubic feet of soil, and calls for compaction of three separate lifts of soil using 25 blows by a 5.5 lb hammer falling 12 inches, for a compactive effort of 12,375 ft-lbf/ft3. 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 of about 56,250 ft-lbf/ft3. Both tests allow the use of a larger mould, 6 inches in diameter and holding 1/13.333 ft3, if the soil or aggregate contains too large a proportion of gravel-sized particles to allow repeatability with the 4-inch mould. To provide about the same theoretical compactive effort (12,320 ft-lbf/ft3 for standard Proctor and 56,000 ft-lbf/ft3 for modified Proctor), the number of blows per lift is increased to 56.IHS, Industry Standards & Regulations. (2010). Retrieved from http://engineers.ihs.com/document/abstract/ZIDGIBAAAAAAAAAA


Alternative compaction testing

The
California Department of Transportation The California Department of Transportation (Caltrans) is an executive department of the U.S. state of California. The department is part of the cabinet-level California State Transportation Agency (CalSTA). Caltrans is headquartered in Sacr ...
has developed a similar test, California Test 216, which measures the maximum wet density, and controls the compactive effort based on the length (in fact the height) of the test sample and not on its volume. The primary advantage of this test is that maximum density test results are available sooner, as evaporation of the compacted sample is not necessary.


References


See also

*
Civil engineering Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewa ...
* Earthworks (engineering) * Geotechnical engineering *
Granular material A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). The constituents that compose gra ...
* Publications in geotechnical engineering * Soil compaction *
Soil mechanics Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and wat ...
{{DEFAULTSORT:Proctor Compaction Test Tests in geotechnical laboratories