Distance Between Test Points (m)
0
25
50
0.400
0.300
0.200
0.100
0
40
80
120
160
Distance Between Test Points (ft)
Figure 5. Variogram of normalized FWD center deflections, LV27 subgrade.
As a follow-up to compiling and assessing
test point separations distances will decrease and
survey results, we hope to minimize the cost for
vice versa. This will reduce testing at unnecessary
overlay design and pavement evaluation by de-
locations and provide more representative cover-
veloping a computer program that optimizes
age of any pavement section for pavement evalu-
the number and location of FWD test points as
ation and overlay design. Furthermore, this
data are collected in the field. The program will
technique will probably minimize lane closure
be based upon a mathematical model that en-
time, thereby improving both employee and
ables quantification of spatial variability (of
public safety.
pavement stiffness). Based upon preliminary
work, this continually adjusting optimal test
point configuration program would optimize
SUMMARY
the FWD testing process by eliminating both
Compilation of survey results from an NDT
undertesting and overtesting (thereby eliminat-
practices questionnaire distributed to state DOTs
ing under- or overdesign), minimize lane clo-
showed that Dynatest FWDs are by far the most
sure time (thereby improving both employee
popular nondestructive pavement testing device.
and public safety), and guarantee that adequate
The current uses for such FWD/NDT devices are
data be collected for pavement evaluation and
pavement overlay design, pavement evaluation
overlay design.
network/inventory, research, void detection, and
load transfer determination. Table 1 summarizes
software and analytical tools used. AASHTO
LITERATURE CITED
guidelines and DARWIN, which uses AASHTO
methods, provide the most frequently used over-
Dynatest (1993) List of FWD Purchasers. Dynatest,
lay design technique. In-house programs are also
Stark, Florida.
used quite often. DARWIN (and AASHTO),
Kestler, M.A., M.E. Harr, R.L. Berg, and D.M.
MODULUS, ELMOD, and in-house programs
Johnson (1994) Spatial variability of falling
constitute the most commonly used methods
weight deflectometer data: A geostatistical
for pavement evaluation.
analysis. In Proceedings, Bearing Capacity of Roads
Most states test fewer than 700 lane-miles per
and Airfields Conference, Minneapolis, Minnesota.
year for overlay design and fewer than 1000 lane-
Smith, R.E., and R.L. Lytton (1984) Synthesis study
miles per year for network level testing. Test point
of NDT devices for use in overlay thickness de-
spacing for both overlay design and network/
sign of flexible pavements. Report No. FHWA/
inventory ranges from 100 to 1000 ft, with outliers
RD83-097, April.
in both categories reaching 3000 ft.
6
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