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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 Mr. The EFWD/Mr ratio was also found to be significantly affected by the backcalculatio method. Furthermore, this ratio was higher at lower Mr values and hence weaker subgrade soils. 1 INTRODUCTION The analytical solution of a three-layer flexible pavement system was derived by Burmister in 1945. KEYWORDS: Flexible pavement system, backcalculation algorithm, deflection sensor configuration. The results of this study showed that the EFWD/Mr ratio ranged from 0.51 to 8.1 for the tested subgrade soils. estimation of elastic modulus of subgrade is not much dependent on the choice of deflection sensor configuration. Statistical models were developed that can relate the laboratory measured Mr to FWD moduli backcalculated (EFWD) using each of the methods considered. The laboratory testing program consisted of conducting repeated load triaxial Mr tests, physical properties, and compaction tests on soil samples obtained from tested sections. This study uses the Modulus 4. The authors developed some recommendations and guidelines to be followed when using these programs in order to minimize layer moduli prediction errors. In addition, the AASHTO and Florida backcalculation equations were used for comparison. A study by Bayomy and Shah 8 was performed on selected backcalculation programs including MODULUS 4.0 and EVERCALC 3.3.
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Three backcalculation software packages were iused to interpret th FWD data: ELMOD 5.1.69, MODULUS 6.0, and EVERCALC 5.0. The tested sections covered the common subgrade soil types found in Lousiana. The field testing program included testing various sections in 10 pavement projects within Louisiana.
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Mr is used in the design and evaluation of pavement structures. Field and laboratory testing programs were conducted to develop models that predict the resilient modulus (Mr) of subgrade soils from the falling weight deflectometer (FWD) test results.