Pavement design is evolving from the experimental American Association of State Highway and
Transportation (AASHTO) Pavement Design Guide to the Mechanistic-Empirical Pavement
Design Guide (MEPDG) (AASHTOWare Pavement ME Design). In the latter method, the
predicted mechanistic responses of the pavement structure (strains and deflections) are
empirically correlated to field-observed distresses. Therefore, mechanistic response data from
instrumented, full-scale test road facilities are essential for the validation and further
development of the MEPDG models. The University of Alberta’s Integrated Road Research
Facility (IRRF) includes an extensively instrumented test road, with a variety of asphalt strain
gauges and earth pressure cells in the unbound layers to capture the flexible pavements’
mechanistic responses to dynamic traffic loading.
This paper focuses on investigating the effect of operational speed and lateral wheel wander on
longitudinal tensile and vertical compressive strain measurements at the bottom of the Hot Mix
Asphalt (HMA) layer (εl and εc) and compressive stress measurements in the granular base
course (GBC) and subgrade (σc). During a field experiment at the IRRF, a test truck with predetermined
axle loads was driven at four different speeds and two symmetric lateral offsets with
respect to the outer wheelpath. Longer load durations (lower loading frequency) were observed
at lower truck speeds in the HMA and unbound layers. Also, the magnitude of εl and εc increased
when speed decreased. Similarly, higher vehicle speed resulted in less σc within the GBC and
subgrade.
Sensitivity of fatigue cracking and rutting models in the MEPDG to operational speed was
investigated in a sensitivity analysis. To do so, an MEPDG-simulation of the test section was
developed using the backcalculated moduli of each layer obtained from Falling Weight
Deflectometer (FWD) test performed at the IRRF. The rate of both alligator cracking and rutting
was found to decrease at operational speed of 60 km/hr. It was also found that the MEPDG
underestimates the effect of speed on the predicted fatigue cracking and rutting.
