referred to as resilient moduli since the load-deformation character-

istics of flexible pavements are resilient (see Section 6.5.1). Also,

because different moduli values were obtained from the Dynaflect and FWD

tests, it was decided to correlate layer moduli predictions with the in

situ penetration tests for both NDT devices.

 The correlations between pavement layer moduli and qc and ED are

presented in Section 7.4.2 and 7.4.3, respectively. The average qc and

ED values for each layer was correlated to the respective NDT tuned

moduli. The first layer was excluded, since the resilient characteris-

tics of asphalt concrete materials are both temperature and rate of

loading dependent.

 The effective pavement thickness (EPT) was defined to be 1 m from

the pavement surface. Materials below this were assumed to have no

effect on traffic-associated pavement performance. This was then used

to determine the thickness of the effective subgrade layer which was

therefore the difference between 1 m and the overlying pavement thick-

ness. This assumption is consistent with the conventional design

practice in which subgrade samples immediately below the subbase layer

are tested for modulus values. Also, other workers have selected

similar depths for use with their penetration tests. For example, Kleyn

et al. (58) considered the depth of 0.8 m for the use of the dynamic

cone penetrometer in road pavements. Briaud and Shields (15) conducted

their pavement pressuremeter tests to a depth of 1.8 m in airport

pavements. Even though EPT could vary with pavement types and stiffness

characteristics of the pavement a value of 1 m was used in this

analysis. The possible effects of this and the general problem of

characterizing the subgrade layer are discussed in Section 7.5.