Evaluating the Light Falling Weight Deflectometer Device for in Situ Measurement of Elastic Modulus of Pavement Layers

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Field and laboratory testing programs were conducted to evaluate the potential use of the light falling weight deflectometer (LFWD) device for measuring the in situ elastic modulus of pavement layers and subgrades. The field tests were conducted on several highway sections selected from different projects in Louisiana. In addition, nine test sections were constructed and tested at the Pavement Research Facility site of Louisiana Transportation Research Center. All sections were tested using the Prima 100 model-LFWD in conjunction with the falling weight deflectometer (FWD), plate load test (PLT), and dynamic cone penetrometer (DCP) tests that were used as reference measurements. Linear regression analyses were carried out on the collected test data to develop models that could directly relate the LFWD stiffness modulus with moduli obtained from FWD and PLT and the DCP penetration rate. In addition, multiple nonlinear regression analyses were conducted to develop models that could predict FWD and PLT moduli on the basis of the LFWD elastic moduli and selected soil properties (moisture content and void ratio) of the tested materials. The results showed that the FWD, PLT moduli, and DCP-penetration rate could be predicted directly with LFWD at a significant confidence level. However, the prediction models were improved when the soil properties were included as variables. Laboratory tests also were conducted to determine the influence depth of the LFWD, and the results of these tests showed that the LFWD influence depth ranged from 270 to 280 mm.