Designing Base and Subbase to Resist Environmental Effects on Pavements

Wednesday, March 21, 2018 - 15:30

Minnesota DOT's current pavement thickness design procedures do not characterize the effects of subgrade soil frost susceptibility. Previous research indicates frost action is the most severe environmental factor on pavement performance. The most accepted mitigation practice is to replace the frost-susceptible material with non-frost-susceptible material to a depth of one-half or more of the frost depth, with silt soils possessing the highest potential for frost heave. MnDOT currently requires minimum total depths of 30 or 36 inches of "frost-free" materials (FFM) for flexible pavements. Limited conclusions with regard to subgrade frost action could be drawn from MnDOT's pavement performance data. Data from the Long-Term Pavement Performance (LTPP) program SPS-8 sites in South Dakota and Wisconsin suggest that lesser FFM depth and greater subgrade silt content correlate well with poorer performance. Data regression based on nine freezing climate zone SPS-8 sites provide a very good fit and a simple-to-use design tool is based on project location, predicted frost depth, and subgrade soil silt content. The required percentage treatment of the predicted frost depth ranges from about 30 percent (0 percent silt) to over 80 percent (100 percent silt). The tool provides a straightforward means to select frost treatment depth that is simple and cost-effective to implement, requires limited additional laboratory testing, and requirements are generally in line with MnDOT's current practices. Short-term and long-term recommendations are provided to help MnDOT expand on the results of this project. The full report is available online at:


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