Use of Load Tests in the Design of Flexible Pavements

    Published: Jan 1948

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    This paper describes a method for utilizing load tests for the design of flexible pavements. Rigid circular plates are used to represent tires of equivalent contact areas, and load bearing values are determined at ¼-in. total deformation.

    The procedure involves four steps as follows:

    1. Load-deformation data are obtained, on top of the subgrade and superimposed sub-base and base layers, with plates of 216, 432, and 800-sq. in. areas.

    2. Using the data thus obtained, load-deformation curves are constructed from which load-bearing values at ¼-in. deformation are selected.

    3. Using the load-bearing values at ¼-in. deformation and the perimeter-area ratios of the plates, straight-line relations are established, between load-bearing value and size of testing plate, for each stage of the layered system. This arrangement of the data constitutes a strength-thickness relation for the three plates used as well as for all intermediate sizes.

    4. This graph is used to determine sub-base and base thicknesses required to handle desired loads on desired plates.

    Two graphs, constructed from field data, are included in the paper and are used to illustrate the application of the design method.

    The paper also discusses, and includes data on, the following phases of the design problem:

    (a) Resistance of densified soils to the destructive forces of nature,

    (b) Elastic deformation as a basis of design,

    (c) Repetitive loading as a basis of design,

    (d) Variation of bearing capacity (strength) with size of testing plate,

    (e) Subgrade bearing capacity (strength) and (strength imparting) increased supporting power of superimposed layers, and

    (f) Effect of loaded plates on surfaces adjacent to the plates.

    Author Information:

    Campen, W. H.
    Manager and Chief Chemist, Omaha Testing Laboratories, Omaha, Nebr

    Smith, J. R.
    Manager and Chief Chemist, Omaha Testing Laboratories, Omaha, Nebr

    Committee/Subcommittee: D18.10

    DOI: 10.1520/STP43945S

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