Effects of freeze-thaw cycle on engineering properties of loess used as road fills in seasonally frozen ground regions, North China

Compacted loess is widely used as fills of road embankments in loess regions of northern China. Generally, densely-compacted loess can satisfy the requirements of embankment strength and post-construction deformation. I lowever, uneven subsidence, pavement cracks and other related damages can affect the integrity of loess subgrade after several years of operation, and even cause some hazards, especially in North China, where the strong freeze-thaw erosion occurs. In this study, cyclic freeze-thaw tests for both densely and loosely compacted loess samples were performed to determine the variation in engineering properties such as volume, void ratio, collapsible settlement, microstructure, and the related mechanisms were addressed. The experimental results showed that an obvious water migration and redistribution occurred within the samples during freeze-thaw cycles. Ice lenses and fissures could be identified in the upper frozen layers of the samples. After freeze-thaw cycles, the dry densities of the nipper layers of samples changed significantly due to strong freeze-thaw erosion. The dry densities decreased for the dense sample and increased for the loose sample. It can be found that dense samples become loose, while loose samples became dense with the increasing number of freeze-thaw cycles. Their related void ratios changed reversely. Both void ratios tended to fall into a certain range, which verified the concept of a residual void ratio proposed by Viklander. The loosening process of densely compacted samples involves the formation of large pores, volume increase and density reduction as well as the related changes in mechanical properties because freeze-thaw cycles may be important contribution to problems of loess road embankments. Adverse effects of freeze-thaw cycles, therefore, should be taken into account in selecting loess parameters for the stability evaluation of road embankment in seasonally frozen ground regions.