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    Volume 39, Issue 6 (November 2016)

    Investigating Stress Dependency of Unbound Layers Using Falling-Weight Deflectometer and Resilient Modulus Tests

    (Received 19 November 2015; accepted 28 June 2016)

    Published Online: 2016

    CODEN: GTJODJ

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    Abstract

    Unbound layer materials, such as base and subgrade, exhibit stress-hardening and/or -softening, which can be determined from their resilient modulus values. However, unavailability of required amount of material and compaction variability between field and laboratory necessitate a need to predict stress dependency of the unbound layers by field tests. This study evaluates stress dependency of unbound layers using a falling-weight deflectometer (FWD) test. The FWD tests were conducted at multi-load levels on several pavement sections. The FWD back-calculated layer moduli are then used to determine bulk and octahedral shear stresses using the layered elastic analysis technique. Next, the regression analysis is performed to interpret the stress-dependent parameters, i.e., regression coefficients of pavement ME's resilient modulus model of nonlinear unbound material. It is observed that stress-hardening is dominant in the case of the base layer, whereas subgrade exhibits both stress-hardening and -softening. This was also confirmed by laboratory resilient modulus tests on both base and subgrade materials in this study. Therefore, it is recommended not to ignore either stress-hardening or -softening during nonlinear modeling of the unbound layers. In addition, in this study, empirical relationships are developed to perform inter-conversion of laboratory resilient and FWD back-calculated modulus incorporating the field state of stresses in base and subgrade.


    Author Information:

    Ahmed, M. U.
    Civil Engineering Department, MSC01 1070, University of New Mexico, New Mexico, NM

    Hasan, M. M.
    Civil Engineering Department, MSC01 1070, University of New Mexico, New Mexico, NM

    Tarefder, R. A.
    Civil Engineering Department, MSC01 1070, University of New Mexico, New Mexico, NM


    Stock #: GTJ20150271

    ISSN:0149-6115

    DOI: 10.1520/GTJ20150271

    Author
    Title Investigating Stress Dependency of Unbound Layers Using Falling-Weight Deflectometer and Resilient Modulus Tests
    Symposium ,
    Committee D04