PAVEMENT DESIGN IN COLD AREAS

A replacement method is described which is based on the CBR design, and the use of insulation in road construction. The subgrade bearing capacity during the thawing period was investigated and design CBR value has been set up for each group of soil characters. The pavement depth and the replacement depth was compared and the larger is taken for the determination of pavement structures. The field CBR tests on subgrade, frost prevention layers and 30 cm thick layer of frost prevention layers above the surface of subgrade, are reported and discussed. Since Roads in Hokkaido show large freezing depth, a replacement depth of roads should be 80 percent of the deepest frost penetration in existing gravel roads. This corresponds to about 70 percent of the frost penetration in the roads which are replaced to full depth with nonfrost grained materials. A frost damage correcting measure is outlined. When the pavement depth (above) is smaller than the standard replacement depth, frost-susceptible materials shall be filled below the subbase course for such a depth of difference. The minimum depth of frost preventing layer shall be 15 cm. The qualities required of replacement materials are listed. Care is urged in the selection of insulating material and the use is noted of extruded polystyrene board on subgrade soil. However, quantitative studies of its' effect on frost action were not performed.