BACKGROUND: Expansive clay soils that are susceptible to shrink and swell, and silty soils that are susceptible to frost heave are found in many parts of the United States. At these locations, these soils serve as the subgrade of the pavement structure. The AASHTOWare Pavement ME Design (formerly DARWin-ME) and the AASHTO Mechanistic-Empirical Pavement Design Guide Manual of Practice (MEPDG) (see Special Note A) provide a methodology for the analysis and performance prediction of new and rehabilitated pavements. Although the performance of these pavements is known to be closely related to properties of the subgrade, the performance predicted by this methodology does not adequately consider the influence of subgrade soils susceptible to shrink/swell and/or frost heave on pavement performance. There is a need to evaluate the procedures contained in the Pavement ME Design and identify or develop enhancements (in the form of modified or new models) to ensure that the procedures appropriately account for the influence of these types of subgrade soils on the performance of new and rehabilitated pavements. Incorporating these enhancements into the Pavement ME Design procedures will allow an improved analysis and design of pavement structures.
OBJECTIVE: The objective of this research is to propose enhancements, as needed, to the Pavement ME Design procedures to better reflect the influence of subgrade soils susceptible to shrink/swell and/or frost heave on pavement performance. These enhancements shall include modifications of the models contained in the Pavement ME Design and/or the development of new models. The research shall address all new and rehabilitated pavement types included in Pavement ME Design.
Phase I: (1) Collect and review information relevant to the influence of subgrade soils susceptible to shrink/swell and/or frost heave on pavement performance, and identify models for addressing such influence. (2) Evaluate the adequacy of Pavement ME Design models to predict the influence of subgrade soils susceptible to shrink/swell and/or frost heave on the in-service pavement performance for a range of relevant factors (e.g., material, environment, and traffic conditions). (3) Based on the findings of Task 2, propose an updated plan to be executed in Phase II to improve the predictive ability of Pavement ME Design by modifying the models contained in the Pavement ME Design and/or developing new models. The plan must address the evaluation of potential models with regard to their ability to predict performance, ease of implementation in Pavement ME Design, and other relevant considerations. The plan must also describe the approach for calibrating and validating the proposed models. (4) Prepare an interim report that documents the research performed in Tasks 1 through 3. Following review of the interim report by the NCHRP, the research team will be required to make a presentation to the project panel. Work on Phase II of the project will not begin until the interim report is approved and the Phase II work plan is authorized by the NCHRP. The decision on proceeding with Phase II will be based on the contractor’s documented justification of the updated work plan.
Phase II: (5) Execute the plan approved in Task 4, and propose enhancements (in the form of modified or new models) to Pavement ME Design to better reflect the influence of subgrade soils susceptible to shrink/swell and/or frost heave on pavement performance. (6) Identify issues affecting implementation of the proposed enhancements (e.g., need for new data elements, new test methods and equipment, and increased effort), and propose possible actions to address these issues. (7) Prepare a final deliverable that documents the entire research effort. The proposed enhancements shall be prepared as a stand-alone deliverable suitable for consideration and adoption by AASHTO. All data used in the research (e.g., for evaluation of potential models and for calibrating and validating identified models) shall be provided, in an electronic format with schema, as an attachment to the final deliverable.
STATUS: Project started on August 15, 2018; research in progress.