UFC 3-260-03
15 Apr 01
e. Consider a subgrade material beneath a facility being evaluated that varies in such a manner
that the facility may be divided into several rather large areas of different subgrade materials. The
in-place CBR values for the entire facility, arranged in ascending order, are as follows: 7, 7, 8, 9, 9, 10,
14, 14, 15, 16, 20, 21, 21, 22, 28, 28, 28, 30, 30, and 31. A study of in-place conditions reveals that the
degree of saturation of the subgrade is about the same for the entire area covered by the facility and that
it is sufficiently high so that the in-place CBR values can be used for evaluation. Preliminary analysis of
these data shows that the statistical distribution for the whole facility is not good and that the values logi-
cally fall into four groups. Each group represents one of the areas of different material; thus, the most
critical area is that represented by the range of values from 7 to 10, and the evaluation should be based
on this area. Since the range is narrow, a formal statistical analysis is not necessary, and a visual
inspection of the figures indicates that a value of 8 or 9 should be selected.
f. Regardless of the number of values available and the method of selecting the evaluation figure,
the number of values and the analytical process used should be described and discussed in the evalu-
ation report in sufficient detail to be easily followed at a later date.
g. Because of certain inherent difficulties in processing samples for laboratory tests and in
performing in-place tests on base-course materials, it is advisable to assign CBR values to certain mate-
rials based on their service behavior, as shown below.
Type of base-course material
Evaluation CBR
Graded crushed aggregate (100 CBR)
100
Water-bound macadam
100
Dry-bound macadam
100
Bituminous course, central plant, hot mix
100
Limerock
80
Bituminous macadam
80
Graded crushed aggregate (80 CBR)
80
Soil cement
80
Sand asphalt
80
Sand shell or shell
80
Open-graded (stabilized or unstabilized)
80
h. The above CBR values should be used when the material meets the quality requirements of the
guide specifications or construction specifications. When the evaluation tests are made less than
3 years after construction and indicate plasticity index values greater than 5, in-place CBR values should
be considered, but no value greater than 50 should be assigned. When tests are made 3 years or more
after construction and indicate plasticity index values greater than 5, the in-place values should be used.
i. When evaluation tests on subbase materials are made less than 3 years after construction and
the tested materials meet the suggested requirements in TI 825-01/AFM 32-1124 (I)/NAVFAC DM 21.10,
the in-place CBR values should be considered, but no value greater than 50 should be assigned. When
tests are made 3 years or more after construction, the in-place values should be used. Cases may
occur where the CBR tests tend to underrate certain cohesionless, nonplastic materials. If records show
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