Stiffness-Based Field-Testing Framework for Design and Evaluation of Pavement Subsurface Layers

Pavement subsurface layers are designed based on the modulus of the subgrade reaction, resilient modulus, or through the California bearing ratio test; yet, the standard method for assessing the condition of as-built soil layers during construction is the nuclear density gauge (NDG) method. The NDG method, however, does not indicate the performance of the pavement sublayers (i.e., strength, stiffness, or modulus) like the parameters used during the design process. This paper discusses the use of the lightweight deflectometer (LWD) and dynamic cone penetrometer (DCP) tests under a proposed stiffness-based field test framework for the construction and evaluation of pavement subsurface layers. Large-scale test sections were built with locally available geomaterials and evaluated with the NDG, LWD, and DCP tests during and after construction. While the results from the NDG tests showed some variability, the LWD test results were more consistent among layers composed of the same material. A correlation was observed between the DCP penetration index and the LWD test parameters (i.e., deflection, dynamic modulus, and impulse stiffness modulus), both unbiased measures of soil stiffness. From this study, the implementation of both devices can provide near-surface layer measurements with the LWD test and post-construction evaluation results with the DCP test that can interchangeably provide the user with a more mechanistic-related condition of the pavement subsurface geolayers.