Technical information

6-8
sections are removed. Data sampling rates should be varied based on the current
‘action’; e.g., use 100 scans per second for APT passes (including when the wheels are
lifted of the ground and returned to the startup location), use 5,000 scans per second
for FWD tests, and record data every 5 to 10 minutes when monitoring environmental
changes. The carriage position relative to the gauge array ought to be recorded at all
time; this information is very important for performing inverse analysis. In the present
study the APT carriage position was only recorded in the longitudinal direction. In
future studies, whenever wander is applied, lateral positions of the carriage should also
be recorded.
(v) Laboratory Work. Standard tests such as soil classification, laboratory
compaction, HMA complex modulus, and resilient modulus for the unbound materials
should be performed. An attempt should be made to employ a large range of
conditions in these tests, e.g., execute the resilient modulus tests at different
compaction and moisture levels. In addition, capabilities to perform more advanced
tests should be developed; e.g., creep and recovery for the HMA in uniaxial (either
tension or compression) or isotropic conditions. In this connection, radial strain
measurements in all mechanical tests should be included. Whenever possible, test
specimens should be fabricated from samples cut or cored from the as-built pavement.
(vi) Field project testing. As discussed in Topic (i) above, field project should be
instrumented during construction by embedding gauges similar to the APT study or by
retrofitting an existing pavement with gauges (e.g., temperature probes and multi
depth deflectometers). Response data in the field may be collected only at certain
times during which the lane will be closed to traffic and a truck of known weight and
speed will drive over the gauge array. It is very important that the applied loading be
accurately positioned in space (
x
,
y
,
z
) and time (t ) relative to the gauges. For
longitudinal positioning, a triggering device is suggested that can sense reflective
targets mounted on the truck; for transverse positioning it may be sufficient to mark
the pavement with lines spaced 1 to 2 in. (25 to 51 mm) apart and take high definition
video of the moving truck. Other tests should be conducted to investigate the overall
structural behavior, as recommended in Topic (iii) above.