1. Light Compaction Equipment
Compaction measurements
Welcome remarks TBD.
01/12/06

2. Measuring compaction = Measuring soil density increase
Soil compaction is among the most complex processes in the construction techniques: Whether a compaction work is efficient or not is not obvious to tell at first sight.
It is first necessary to determine a reference to compare with: This is the objective of the Proctor test applied to a soil sample.
It is time afterwards to measure the compaction on the jobsite. Several techniques exist:
Physical soil density measurement:
Sand Cone
Balloon Density Meter
Shelby Tube
Nuclear Gauge density measurement.
Soil stiffness
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3. Proctor test Define the reference 100% density by a laboratory test
A compaction measurement is only valid when it is looked at in relation with a reference value: the value defined by the Proctor test.
E.g. Two different types of soil, A and B. A is recognized to have a good stability (bearing) properties when its density reaches 3 kg/dm³. B, which is of a heavier composition, will be stable when compacted at 4 kg/dm³. These “100% density” values are actually determined by the Proctor Test.
Taking a sample of soil A on a jobsite and measuring a density of 2.7 kg/dm³, we can tell that its compacity is of 90%. (The general contractor will usually settle the compaction objective as a percentage value of the Proctor reference: 97% or 98 %) A B
Composition A B X
Poctor max dens.
3 kg/dm³
4 kg/dm³
? kg/dm³
Sample meas. d.
2.7 kg/dm³
Relative density
90 %
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4. Proctor test Laboratory
In most cases, the soil composition of a jobsite is not known. It is necessary to realize a Proctor test in a laboratory in order to measure the reference (100%) density value.
It is defined as the density after the following treatment of the dry soil:
2.495 kg
30.5 cm
0.94 dm³
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5. Compaction measurement On site
Density measurement: Sand cone
A small cubic hole (~ 6” side, ~ 15.2 cm) is dug in the compacted soil to be tested. The soil is removed, weighed, then dried and weighed again to determine its moisture content.
Moisture = Water wt / Dry soil wt.
The exact volume of the hole is measured by pouring dry sand in the hole using the sand cone.
The soil sample density is easily calculated by dividing the dry weight and the volume [kg/dm³].
This value is compared with the maximum Proctor density to calculate the relative density [%].
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6. Compaction measurement On site
Density measurement: Core test
The principle of density calculation is very similar to the sand cone.
But there is no volume measurement to be done since the inside volume of the cylinder that will remove the sample is calibrated.
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7. Compaction measurement On site
Nuclear Gauge
The meter uses a radioactive isotope source (Cesium 137) at the soil surface or from a probe placed into the soil (direct transmission).
The isotope source gives off photons (γ rays) which radiate back to the mater’s detectors on the bottom of the unit.
Dense soil absorbs more radiation than loose soil and the readings reflect overall density.
Water content can also be read, all within a few minutes.
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8. Compaction measurement On site, new technique
Soil Stiffness
This field-test method is a very recent development that replaces soil density testing.
Soil stiffness is the ratio of force-to-displacement.
Testing is done by a machine that sends vibrations into the soil and then measures deflection of the soil from the vibrations.
This is a very fast, safe method of testing soil stiffness.
There are chances in the future that the demand of the general contractor will not be anymore on the density but on soil stiffness.
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