Measured and Theoretical Pressures in Base and Subgrade Layers under Dynamic Truck Loading

Abstract

As mechanistic-empirical (M-E) design continues to advance toward full implementation by state agencies, there is a need to asses the accuracy of the load-component of flexible pavement M-E design and the common practice is to use a layer elastic approach to predict pavement responses under load. Concerns regarding accuracy of this type of model arise when considering unbound materials exhibiting non-linear behavior, visoelastic hot-mix asphalt (HMA) materials and dynamic loads applied by moving traffic. Despite this, layered elastic models continue to be the state-of-the-practice for most pavement design and analysis applications. The objective of this study was to assess the accuracy of a layered elastic model with respect to measured pavement response under live traffic. Specifically, eight test sections at the National Center for Asphalt Technology (NCAT) Test Track were instrumented to measure vertical pressures in the unbound base and subgrades. The test sections consisted of various HMA thickness and used modified and unmodified asphalt binders. Material properties were established using backcalculation of falling weight deflectometer (FWD) data. The test sections were then simulated with the layered elastic computer program, WESLEA. The simulations also included actual loading configurations applied by the tractor-triple and single trailer vehicles used at the Test Track. The study focused on in-tact pavements (i.e., no cracking) and comparisons between theoretical and measured pavement responses were made over a wide range of environmental conditions and the two different truck load configurations. A unique approach was developed to account for the natural wander of the vehicles relative to the fixed location of the pressure gauges.