CORPS OF ENGINEERS' DESIGN OF HIGHWAY PAVEMENTS IN AREAS OF SEASONAL FROST

In this summary of the frost condition design method and discussion of the current citeria for highways, definitions are presented of the specialized terms used by the Corps of Engineers and ice segregation and the frost susceptbility of soils are reviewed. The conditions necessary for ice segration are listed and an expression is presented of the potential intensity of ice segregation in soil as an empirical function of grain size. The results are set forth of laboratory frost-susceptibility tests performed on natural soil gradations ranging from well graded gravels to fat clays using the standardized freezing procedure. A table is presented of soils classified (into 4 groups) for frost design purposes. Curves used to illustrate the relationship between air-freezing index and frost penetration into granular, non-frost susceptible soil beneath pavements kept free of snow and ice for freezing indexes below 800, may be used to estimate values of frost penetration beneath paved areas. A potentially troublesome water supply for ice segregation is present if the highest ground water table at any time of the year is within 5 ft of the proposed subgrade surface or the top of any frost susceptible base materials. Three pavement design methods derived from two basic concepts (control of surface deformation resulting from frost action; or provision of adequate heaving capacity during the most critical climatic period) are outlined. They are: the Complete Protection Method, Limited Subgrade Frost Penetration Method and the Reduced Subgrade Strength Method. A design method (developed in 1961) is detailed which expresses the loading on several wheel and traffic configurations reduced to equivalents in terms of repetitions of an 18,000-pound load on a single axle equipped with dual tires. By expressing all vehicular traffic in terms of this basic loading and incorporating several simplifying assumptions, pavement design for highways was reduced to a function of load application and subgrade strength (concrete flexural strength is also considered in the case of PCC pavements).