Use of FWD multi-load data for pavement strength estimation

HWY-00-04The objective of this study is to develop a mechanistic-empirical method for assessing pavement layer conditions andestimating the remaining life of flexible pavements using multi-load level Falling Weight Deflectometer (FWD) deflections. Adynamic finite element program, incorporating a stress-dependent soil model, was developed to generate the synthetic deflectiondatabase. Based on this synthetic database, the relationships between surface deflections and critical pavement responses, such asstresses and strains in each individual layer, have been established. A condition assessment procedure for asphalt pavements thatuses multi-load level FWD deflections has been developed using these relationships. The verification study was conducted usingfield data. The results indicate that the proposed procedure can estimate the base and subgrade layer conditions. It was foundfrom 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 inany apparent nonlinear behavior of the subgrade in aggregate base pavements. The study also indicated that the deflection ratioobtained from multi-load level deflections may predict the type and quality of the base/subgrade materials. With regard to thecondition assessment of the asphalt concrete (AC) layer, the AC layer modulus and the tensile strain at the bottom of the AClayer 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. Thedrastically increasing trend in fatigue cracking with time may not be predicted accurately using the proposed procedure. Suchtrends may be due to the environmental effects and the inconsistent distress measurements. Predicted rut depths using multi-loadlevel deflections show good agreement with measured rut depths over a wide range of rutting. However, the procedure usingsingle load level deflections consistently underpredicts the rut depths. It was concluded that the rutting prediction procedureusing multi-load level deflections can estimate an excessive level of rutting quite well and, thus, improve the quality of predictionfor rutting potential in flexible pavements.The layer condition assessment procedure and the remaining life prediction algorithms developed in this project wereincorporated into APLCAP (Asphalt Pavement Layer Condition Assessment Program) version 2.0, the VisualBasic programdeveloped under the NCHRP 10-48 project