Performance of Montana Highway Pavements During Spring Thaw

摘要

Highway pavements in seasonal frost areas undergo annual freeze-thaw cycles. Pavements constructed for the design load capacity can become weak during spring thaw. In 1995, the Montana Department of Transportation (MDT) initiated a study on developing road restrictions during the spring thaw. Selected sites throughout Montana were instrumented. Field measurements of deflection, moisture, and temperature were made during the winter/spring of 1996-1997 and 1997-1998. The analysis determined thaw-weakening characteristics of the sites and developed subgrade modulus values for use in future design of pavement structures in Montana. Based on the moisture data, the base course layers at Dickey Lake, Wolf Point, Scobey/Redstone, and East Glacier are prone to thaw weakening. Deflection data indicate that the bases at Bull Mountain, Swan Lake, and Scobey/Redstone may be prone to thaw weakening. The subgrade at Dickey Lake, East Glacier, Bull, Mountain, Swan Lake, and Scobey/Redstone may also be prone to thaw weakening. The length of thaw weakening varied from 4 days (Scobey/Restone) to 3 weeks (East Glacier). This report provides a general description of the test sites, the measurements and analysis of the data, results of the analysis, and recommendations based on the results. In addition, the report quantifies the effects of thaw weakening on typical roads in Montana based on deflection, surface and subsurface moisture, temperature, and other atmospheric measurements taken by MDT.