UFC 3-260-03
15 Apr 01
(1) Moisture-Content Determinations. The strength of base courses composed of substantial
portions of fine materials is governed by the moisture content of the fine fraction. The fine fraction is that
portion passing any of several sieve sizes ranging from 0.075 to 4.75 millimeters (No. 200 to No. 4). For
the purposes of this document, material passing the 0.42-millimeter (No. 40) sieve has been selected as
the critical portion. This is the same sieve on which separations are made for liquid and plastic limit deter-
minations. The moisture content of both the material passing the 0.42-millimeter (No. 40) sieve and the
total sample should be determined and shown in the tables of test data. If it is impractical to separate the
material at the 0.42-millimeter (No. 40) sieve without affecting the moisture present, an absorption test
following ASTM C 127 should be performed. The percentage of absorption thus determined can be con-
sidered the moisture content of the coarse fraction, permitting arithmetic determination of the moisture
content of the remainder (assuming all other moisture to be in this finer fraction). An indication of the sta-
bility of the base-course material can be obtained by comparing the moisture content of the material pass-
ing the 0.42-millimeter (No. 40) sieve with the liquid limit of the material. If the moisture content is near
the liquid limit, the material can be considered unstable. Should the moisture content exceed the liquid
limit, the base material will be very unstable if appreciable percentages of fines are present.
(2) CBR Tests. Considerable judgment must be used in selecting test locations in the test pit.
In selecting test locations in the pit, the CBR piston should be placed so that the surface to be penetrated
represents an average condition of the surface being tested and should not be set on unusually large
pieces of aggregate or other unusual materials. It is also general practice to space the CBR tests in the
pit so that the areas covered by the surcharge weights of the individual tests do not overlap. These tests
should be performed on the surface and at each full 152-millimeter (6-inch) depth (especially if a strength
problem is suspected) in the base and subbase courses, on the surface of the subgrade, and on under-
lying layers in the subgrade as needed. Density and moisture-content determinations should be made in
the subgrade at 305-millimeter (1-foot) intervals to a total depth of 1.2 meters (4 feet) below the surface of
the subgrade. The results of the density and moisture tests at these depths should be used to ascertain
whether there is a need for additional CBR tests. The tests should be so located in the pit that the density
determinations are performed between adjacent CBR tests. Three in-place CBR tests in test pits should
be performed at each elevation tested. However, if the results of these three tests do not show reason-
able agreement, three additional tests should be made. A reasonable agreement between three tests
where the CBR is less than 10 permits a tolerance of 3; where the CBR is from 10 to 30, a tolerance of 5;
and where the CBR is from 30 to 60, a tolerance of 10. Above a CBR of 60, variations in the individual
readings are not of particular importance. For example, actual test results of 6, 8, and 9 are reasonable,
and their average is 8; results of 23, 18, and 20 are reasonable, and their average is 20. If the first three
tests do not fall within this tolerance, then three additional tests are made at the same location, and the
numerical average of the six tests is used as the CBR for that location. Generally, CBR values below
about 20 are rounded off to the nearest point; those above 20 are rounded off to the nearest five points. A
moisture-content sample should be obtained at the point of each penetration.
(3) Penetrometer Tests. The two basic types of penetrometer tests that can be used to evalu-
ate pavements are the ECP and the DCP. The ECP is located within a C-130 transportable vehicle and
measures the shear strengths of the various subsurface material layers. The ECP cone point is hydrau-
licly pushed through the pavement structure typically to a depth of 1.52 meters (5 feet) at a rate of
20.3 millimeters (0.8 inches)/second. The ECP can provide valuable information pertaining to the pave-
ment structure including bearing strength (correlated to CBR), layer thicknesses, and material classifica-
tion. The DCP is a hand-held portable penetrometer device designed to penetrate soils to a depth of 0.99
meters (39 inches). The cone tipped rod is driven into the ground by raising an dropping a 7.97-kilogram
(17.6-lb) hammer. Data are collected in terms of a DCP index value (mm of penetration/ blow). The index
can then be correlated to CBR using derived relationships. Pavement layer thickness can be determined
by examining zones of uniform strength 25.4 millimeter (1 inch) (DCP) diameter hole is drilled through the
asphalt concrete (AC) wearing surface to the top of the base layer. The test device is then lowered to this
point to begin the test sequence. Detailed test procedures and correlations for using the ECP and DCP
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