Revising the Method for Calculating the Subgrade Bearing Capacity of Paved Roads on Embankments during the Thaw Season

Abstract

In cold, snowy regions in Japan, subgrade bearing capacity (described by design CBR) has been calculated in consideration of a possible drop in the capacity during thawing periods. However, because the bottom of the subgrade of a pavement on embankment is at a relatively great distance from the groundwater level, it is assumed that groundwater supply to subgrade that causes freezing is unlikely to occur. Therefore it is estimated that the subgrade bearing capacity of pavements on a high embankment may not drop even during thawing periods. This study describes a design method for design CBR of pavements on embankments in consideration of embankments heights. By introducing design CBR values that correspond to various embankment heights, pavement can be designed in a more cost-effective way. The study found the following: 1) on embankments with a height of 6 m or more, thawing periods were found to have only a slight impact on the subgrade bearing capacity. The field CBR can be used directly as the design CBR, 2) on embankments with a height of 3 - 6 m, the bearing capacity was confirmed to have dropped during thawing periods. The field CBR should be multiplied by 0.77 to obtain the design CBR, 3) on embankments with a height of 3 m or less, as the subgrade bearing capacity showed significantly varying degrees of deterioration, freezinglthawing tests should be made before CBR tests are conducted to decide the appropriate multiplication factor.