The depth of the pressure plate, and possibly the material lying above it (HMA
versus unbound granular materials) had an effect on the repeatability of pressure
measurements. For the pressure cells atop the granular base layer, 95% of the
measurements directly under FWD load were within 0.78 psi of each other. For
the pressure cells atop the subgrade layer, 95% of the measurements directly
under FWD load were within 0.29 psi of each other.