Technical information

6-7
so that two new loading modes can be applied to the surface of the pavement:
horizontal (shear) and turning (torsion); these will allow the study of intersection
conditions. An investigation to study the effects of various tire pressures should also
be targeted. In this connection, a way to measure the actual loading area and
distribution of stresses under the APT tires should be explored.
(iii) Structural Behavior. Completed structures in the APT should be tested using the
Dynamic Cone Penetrometer, but also using more advanced geotechnical equipment
such as the pressuremeter (cavity expansion). FWD testing should periodically be
performed while recording the entire time history of the loading and deflections. At
the same time, the responses captured by the embedded gauge array should also be
recorded. Vertical surface deflection during APT testing and also during FWD testing
ought to be monitored with external LVDTs. In addition, stand-alone accelerometers
and geophones should be attached to the pavement surface to supplement the LVDTs.
During all experiment types rutting measurements should be collected; more profiles
ought to be collected at the initial stages of the experiment where most of the rutting is
accumulated. The first profile measurement, taken before any passes are applied,
should be repeated several times for each cross section since these are used as
reference for all other measurements and hence need to be determined at a higher
accuracy level. A method should be found for measuring surface profiles such that the
loading system does not have to stop; this will facilitate the study of permanent
deformation development. A systematic way to detect and record cracks as they
appear (and when they appear) on the surface should be found; in this connection, a
method should be developed to ascertain whether the observed cracks are so-called
‘bottom up’ or ‘top down’. Friction testing in the APT should be routinely performed,
e.g., using the Circular Texture Meter (ASTM E-2157) and the Dynamic Friction
Tester (ASTM E-1911). This type of data may be used to investigate the effects of
temperature, wheel wander, tire type, and loading intensity on frictional attributes.
With additional friction data from the corresponding field study, a scheme may be
developed for using APT experiments to forecast friction performance.
(iv) Data Logging. All types of available data should continuously be recorded from
the very instant of gauge installation, throughout all testing modes, until the test