Use of falling weight deflectometer multi-load data for pavement strength estimation
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2002-06-01
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Alternative Title:Use of FWD multi-load data for pavement strength estimation
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Edition:Final Report; July 1999 - June 2001
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Abstract:The objective of this study is to develop a mechanistic-empirical method for assessing pavement layer conditions and
estimating the remaining life of flexible pavements using multi-load level Falling Weight Deflectometer (FWD) deflections. A
dynamic finite element program, incorporating a stress-dependent soil model, was developed to generate the synthetic deflection
database. Based on this synthetic database, the relationships between surface deflections and critical pavement responses, such as
stresses and strains in each individual layer, have been established. A condition assessment procedure for asphalt pavements that
uses multi-load level FWD deflections has been developed using these relationships. The verification study was conducted using
field data. The results indicate that the proposed procedure can estimate the base and subgrade layer conditions. It was found
from the study for the nonlinear behavior of a pavement structure that an FWD test with a load of 12 kip or less does not result in
any apparent nonlinear behavior of the subgrade in aggregate base pavements. The study also indicated that the deflection ratio
obtained from multi-load level deflections may predict the type and quality of the base/subgrade materials. With regard to the
condition assessment of the asphalt concrete (AC) layer, the AC layer modulus and the tensile strain at the bottom of the AC
layer were found to be better indicators than deflection basin parameters.
The procedures for performance prediction of fatigue cracking and rutting were developed for flexible pavements. The
drastically increasing trend in fatigue cracking with time may not be predicted accurately using the proposed procedure. Such
trends may be due to the environmental effects and the inconsistent distress measurements. Predicted rut depths using multi-load
level deflections show good agreement with measured rut depths over a wide range of rutting. However, the procedure using
single load level deflections consistently underpredicts the rut depths. It was concluded that the rutting prediction procedure
using multi-load level deflections can estimate an excessive level of rutting quite well and, thus, improve the quality of prediction
for rutting potential in flexible pavements.
The layer condition assessment procedure and the remaining life prediction algorithms developed in this project were
incorporated into APLCAP (Asphalt Pavement Layer Condition Assessment Program) version 2.0, the VisualBasic program
developed under the NCHRP 10-48 project.
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