Characterizing Permanent Deformation of Alaskan Granular Base–Course Materials

Permanent deformation of granular base–course materials under repeated vehicle load is an important characteristic that is required to be considered in pavement design. In Alaska, due to the extreme climatic condition, the granular base–course materials in a pavement structure usually undergo significant permanent deformation, which is typically reflected by rutting, cracking, and eventually pothole problems on the pavement surface in spring. Over the years, research efforts on the permanent deformation of base materials, especially for cold regions pavements, have been very limited. To investigate the permanent deformation of granular base–course materials in cold regions, a series of one-dimensional frost heave tests under two extreme water access conditions (i.e., limited and free water access) were conducted on Alaskan granular materials with different fines and initial moisture contents using a one-dimensional frost heave cell. After the freezing process, the repeated-load triaxial test was then performed to investigate the permanent deformation under frozen and subsequent nonfrozen conditions. Test results indicated that frost heave and subsequent permanent deformation of base-course materials were highly dependent on the water access condition during freezing. The fines and water contents, temperature, temperature gradient, stress state, and their coupling effect also played important roles in the permanent deformation of the base-course materials. In addition, regression analyses using a mechanistic-empirical design guideline and Sweere models were performed to predict the permanent deformation of the granular base–course materials with consideration of the influences of fines content, water content, and temperature conditions under thawed and frozen conditions. Compared with the equation from the guideline, the Sweere model provided a better prediction in the material permanent deformation under the unfrozen condition. Using the guideline equation may lead to inaccurate prediction of permanent deformation, especially for granular base–course materials at a relatively higher water content.