Estimation of Resilient Modulus of Subgrade Soils Using Falling Weight Deflectometer

Abstract

Field and laboratory testing programs were conducted to develop models that predict the resilient modulus (M_r) of subgrade soils from the falling weight deflectometer (FWD) test results. M_r is used in the design and evaluation of pavement structures. The field testing program included testing various sections in 10 pavement projects within Louisiana. The tested sections covered the common subgrade soil types found in Louisiana. Three backcalculation software packages were used to interpret the FWD data: ELMOD 5.1.69, MODULUS 6.0, and EVERCALC 5.0. In addition, the AASHTO and Florida backcalculation equations were used for comparison. The laboratory testing program consisted of conducting repeated load triaxial M_r tests, physical properties, and compaction tests on soil samples obtained from tested sections. Statistical models were developed that can relate the laboratory measured M_r to FWD moduli backcalculated (E_FWD) using each of the methods considered. The results of this study showed that the E_FWD/M_r ratio ranged from 0.51 to 8.1 for the tested subgrade soils. Furthermore, this ratio was higher at lower M_r values and hence weaker subgrade soils. The E_FWD/M_r ratio was also found to be significantly affected by the backcalculation method. The results of the regression analysis showed that among all backcalculated FWD moduli, those backcalculated using ELMOD 5.1.69 software had the best correlation with M_r. Furthermore, the results showed that the M_r prediction was significantly enhanced when soil properties were included as variables within the regression model.

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