SEASONAL EFFECTS ON THE STRENGTH OF PAVEMENT STRUCTURES

Results are presented from monitoring and predicting changes in subgrade resilient modulus with season of the year for test sites on the U.S. Forest Service road system. Data collection involved measuring deflection, subgrade moisture content, and soil suction over an 18-month period at four test sites located in Washington and Oregon. In addition the pavement materials (asphalt concrete and base and subgrade materials) were sampled and a series of laboratory resilient modulus tests was conducted on each sample. The laboratory and field data were used to develop methods of predicting changes in subgrade stiffness (strength) over time. The two most promising methods were those obtained from regression equations developed from the laboratory test data for the pavement materials and appropriate elastic-layered computer programs and a hand-calculation method based on deflection measurements.