CHAPTER 4
SIMULATION AND ANALYSES OF NDT DEFLECTION DATA
4.1 BISAR Simulation Study
4.1.1 General
The Dynaflect and FWD loading-geophone patterns were simulated in
the BISAR elastic-layer computer program to predict surface deflection
data for four-layer pavement systems. A flexible pavement structure was
modeled as a four-layer system with parameters shown in Figure 4.1.
The selection of layer thicknesses and moduli was based on typical
ranges in parameters representative of Florida's flexible pavement
systems. In general, the limerock base and stabilized subgrade thick
nesses were fixed at 8 in. and 12 in., respectively. Table 4.1 lists
the range of layer parameters used in the theoretical analysis. The
subgrade was generally characterized as semi-infinite in thickness with
an average or composite modulus of elasticity. However, the effect of
bedrock at shallow depth was also assessed by varying depth to bedrock
in a five-layer system. Poisson's ratio was fixed at 0.35 for all the
pavement layers since it has negligible effect on computed deflections.
In using the layered theory to generate and analyze NDT deflection
data certain assumptions had to be made. The following assumptions were
made with the use of the BISAR program:
1. Pavement materials are homogeneous, isotropic, and linearly
elastic. Therefore, the principle of superposition is valid for
calculating response due to more than one load.
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