Backcalculation programs are used for evaluation of
pavement layer moduli from falling weight deflectometer
(FWD) measurements. In this study, a comparison of two
programs with different calculation methods, Modulus and
Elmod, is made using deflection data derived from 43
SHRP-LTPP (Strategic Highway Research Program, Long-Term
Pavement Performance) test sections.
First, a brief look is made into the material models,
which describe the behaviour of pavement layer materials.
Basic concepts of the two backcalculation programs used
in this study, Modulus and Elmod, are discussed, and
collection of input data for the programs is described.
From a comparison of backcalculated layer moduli from the
two programs at Finnish standard wheel load of 50 kN, it
is concluded that higher subgrade modulus values are
obtained with the Elmod-program than with the
Modulus-program. Consequently, the Modulus-program yields
higher values for asphalt layer modulus than the
Elmod-program. Variation in backcalculated layer moduli
is somewhat greater within the Modulus-program than the
Stress-sensitivity of paving materials was studied by
using the FWD at four different loading levels. The base
course modulus was found to be the most stress-sensitive
of pavement layers, since the stress level is also
highest in the base course of unbound pavement layers.
Critical strains were calculated using the linear program
(BISAR) with layer moduli from the Modulus-program as
input and with the Elmod-program. It was found, that
calculated strains from the two programs agree very well,
even though the calculated moduli are quite different.
Calculated strains from FWD loading were compared with
measured strains under moving wheel load from the field
at Virttaa test site. The differences between the two are
most likely due to differences in the loading conditions
and in the method of analysis.
|Place of Publication||Espoo|
|Publisher||VTT Technical Research Centre of Finland|
|Number of pages||68|
|Publication status||Published - 1994|
|MoE publication type||Not Eligible|
|Series||VTT Tiedotteita - Meddelanden - Research Notes|
- flexible pavements
- Falling weight deflectometer
- modulus of elasticity
- stress sensitivity
- nondestructive testing