How a pavement responds to applied stresses is the
combined result of loading,
environment,
subgrade and pavement material
characteristics. This section presents the typical stresses and
deformations experienced by an HMA pavement structure under load.
Stress
The stresses that occur in a HMA pavement under load are quite complex; routine calculation of
these stresses is a recent development.
Using a basic two-dimensional layered elastic model, the basic relationships
between layer stiffness and stress for a two-layer flexible pavement structure
is shown in Figure 1.
Figure 1: Typical Two-Layer
Flexible Pavement Stresses as Calculated by a Two-Dimensional Linear Elastic Model.
Click the yellow boxes to view different stresses. Note that "E" refers to
a layer's stiffness.
Deflection
HMA pavements are often described as "flexible"
because they deflect under load. Figure 2 shows schematically how
pavements deflect under load.
FWDs can be used to
accurately determine deflection characteristics of in-service pavements.
Figure 2: Schematic Showing
Deflections for Different Pavement Thicknesses. The same HMA material
characteristics are assumed for each graph - only the thickness varies.