UFC 3-260-03
15 Apr 01
(2) Flexible Pavement Procedure. When a nonrigid overlay on rigid pavement is evaluated
using the flexible pavement evaluation procedure, strength and thickness values should be selected in
accordance with the procedures discussed in chapter 5 for flexible pavements.
c.
Modulus of Soil Reaction, k .
(1) The selection of a representative k value can be made in much of the same manner as
that used in the selection of R values; however, generally less test data will be available. For evalua-
tion purposes, the k value should be limited to 500 pci. An average k value is computed for each
pavement feature. There will be instances where k values will be considerably higher or lower than the
average of the majority of values, in which case a thorough study of foundation conditions should be
made at this location to determine whether the test was erroneous or whether the foundation actually is
nonuniform. If the test is found to be erroneous, the unusually high or low value should be discarded; if
the foundation is actually nonuniform, a more extensive testing program may be needed to select a
representative k value. Saturation correction will not be made for k values since the material will have
likely reached and equilibrium moisture content.
(2) The pavement foundation can be investigated using an ECP or a DCP. Each test device
can be used to determine the bearing capacity of a pavement structure at various depths. The ECP
device is mounted in a test van and consists of a cone-tipped rod that is hydraulically pushed into the
ground at a rate of 20.3 millimeters (0.8 inches)/sec. The DCP is a hand-held device that drives a cone-
tipped rod into the ground by repeatedly dropping a 7.97-kilogram (17.6-lb) hammer. Penetration mea-
surements and hammer blow counts are typically made at 25.4-millimeter (1-inch) penetration intervals
using the DCP. The ECP device automatically records the penetration data into a computer system.
Both devices correlate the rod penetration to resistance strength (CBR) by using derived correlations.
The CBR of the pavement layers can be converted to Young's Modulus by multiplying it by 1500 or can
be converted to k by using Figure 3-5. Detailed test procedures and correlations for using the ECP and
DCP devices are provided in Appendix B.
.
d. Limiting Conditions.
(1) When conditions do not indicate concrete or soil of normal physical properties, the evalu-
ation must be modified accordingly. Ideal conditions seldom exist, and full consideration should be
given to the probable influence of factors such as those outlined below. The narrative portion of the
evaluation report should contain a discussion of the effect that any of the following factors might have on
the evaluation of the pavement:
(a)
High moisture absorption and shrinkage of the concrete.
(b)
Extremely high daily variation in temperature.
(c)
Wide variation in the flexural strength within a given pavement section of facility.
(d) Heterogeneous subgrade, base, or moisture conditions resulting in wide variations in
modulus of soil reaction values.
(e) Nonrigid overlays (bituminous concrete and flexible overlay) that do not meet design
requirements for flexible pavements.
(f)
Unsatisfactory load transfer at the joints.
6-2
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