Shrink/swell of expansive clay soils affects pavements from the Gulf of Mexico to the Canadian border including Texas, Oklahoma, Colorado, Arkansas, Louisiana, Mississippi, Alabama, New Mexico, Montana, North Dakota, and South Dakota. These states have significant montmorillonite clay minerals and evapotranspiration may exceed precipitation. The impact of the shrink/swell behavior is differential changes in moisture and vertical elevation from the center of the pavement to the paved edge. This variation results in increased pavement roughness over time.
For states in the northern half of the country, frost heave may also significantly affect pavement smoothness, especially when silty soils are present. In these areas, the freezing boundary will extend into the subgrade soils. Moisture will accumulate and freeze into “frost lenses.” As long as the subgrade remains frozen, the roadway is able to carry heavy loads. When the lenses thaw in the spring, the liquid water flows downward, leaving a void where the lens existed. The void collapses, causing a pavement failure that extends through the full depth of pavement structure. The frost heave issue affects ride quality in at least 15 states along the northern tier, and may affect additional states at higher elevations or in years with unusually cold winters.
Currently in the AASHTO Pavement Mechanistic-Empirical (ME) Design program, frost heave and shrink/swell are empirically predicted from other climatic variables, including freezing index, average annual precipitation, soil plasticity index, and percent passing the number 200 sieve; all of which are used to develop a site factor term. This term, along with the initial IRI for each site and calculated pavement distresses are used to estimate the International Roughness Index (IRI) at time t. The development of improved shrink/swell and frost heave models will greatly enhance the MEPDG methodology.
The objectives of the research are to (1) Develop a new ME model or improve upon an existing ME model for predicting shrink/swell movement in expansive clay soils under pavements, (2) Develop a new ME model or improve upon an existing ME model for predicting movement of pavement from the formation and thawing of frost lenses, and (3) Harmonize the shrink/swell and frost heave models into a single model for predicting overall pavement smoothness deterioration.