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 Mechanistic-Empirical (ME) Design (formerly DARWin-ME) and the AASHTO Mechanistic-Empirical Pavement Design Guide Manual of Practice (MEPDG) 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.

Under NCHRP Project 01-59, “Proposed Enhancements to Pavement ME Design: Improved Consideration of the Influence of Subgrade Soils Susceptible to Shrink/Swell and/or Frost Heave on Pavement Performance,” Arizona State University was asked 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. The research team (1) evaluated 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), (2) proposed a plan to improve the predictive ability of Pavement ME Design by modifying the models contained in the Pavement ME Design and/or developing new models, (3) proposed 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, (4) identified issues affecting implementation of the proposed enhancements, and (5) prepared draft language for consideration by AASHTO to incorporate the research results in the next update of the AASHTO MEPDG.

In addition to the conduct of research that documents the entire research effort published as NCHRP Research Report 1096, supplemental information for each corresponding chapter (Appendices 1-13) is available on the TRB website at www.trb.org.