compaction testing lecture2-4

8/15/2019 Compaction Testing Lecture2-4

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Part 4

COMPACTIONTESTING


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Compaction tests results vary with the inputcompactive effort , usually measured in foot-poundsper cubic foot of soil. The line of optimum moisture contents is usually

around 85% saturation and the optimum moisturecontent decreases with increasing compactive effort.

Which Test AreYou Using?

Standard Proctor 12,400 ft-lbs/ft 3

California Test 216-F 37,000 to 44,000 ft -lbs /ft 3

Modified Proctor 56,250 ft-lbs/ft3

The most importantfigure in this lecture

coinc ide with 85% saturation


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The Standard Proctor test (ASTM D698) employs 12,400ft-lbs/ft 3 of soil , while the Modified Proctor (ASTMD1557) uses 56,250 ft-lbs/ft 3. This typically leads tovariances between 8% and 11%, as shown above.


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Comparisons between Modified Proctor, Standard Proctor, 15-blowProctor, and Porter static compaction tests on samples of sil t and

clayey sand by the Army Corps of Engineers in 1945.

8%differencein clayey

sand

10%difference in

silt


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SPECTURM OF CURVES

The maximum achievable density depends onthe type of material, as well as the input energyduring compaction. It is commonly used for

diatomaceous earth and halyositic clays.


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Average maximum dry unit weight and optimum moisturecontent achieved by standard Proctor Tests (ASTM D698) withplastic l imit (PL) and l iquid limit (LL). This is a key figure toconsult when compacting expansive clay soils. Taken from

“ Factors Influencing Compaction” (1962), HRB Report 319.


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Curve Fitting and SpeedyMoisture Meters

Family of expected wetdensity compactioncurves , based on 18,000compaction tests

compiled by the OhioDOT

The Speedy MoistureMeter is a portablesystem comprising avessel with an integral

pressure gauge aweighing scale in aportable case.

A small sample of the material isprepared, weighed andplaced into the vessel. The reagent isthen added and the vessel is sealed andshaken to mix the reagent with the

sample.


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Compaction curves should be prepared for all types of soil inthe project area, before earthwork commences. If differentsoils are mixed, then “ check points” should be calculated toascertain the optimum moisture level for the soil mixturebeing placed and tested. A great deal of judgment isrequired when performing such work.


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Most field compaction tests are now made using nuclear densitygages that employ a cesium element.Nuc gages can have signif icant errors if the extendable probe islocated next to a rock > 3 inches across. In rocky fills the operatorshould always rotate the probe 90 degrees and take a secondreading, recoding the lower of the two values.

compaction testing lecture2-4

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