Effects of freeze-thaw on the water-heat process in a loess subgrade over a cut-fill transition zone by laboratory investigation

The cut-fill transition is a common subgrade structure in road construction. In seasonally frozen ground, the loess subgrade over cut-fill transition experiences some problems, such as differential deformation, which may largely be caused by water migration due to freeze-thaw action. The water-heat process in the cut-fill transition material during different seasons was analyzed by undertaking a laboratory study that modeled the temperature and moisture changes within loess subgrade material subjected to 15 freeze-thaw cycles. As the number of freeze-thaw cycles increased, a steady temperature profile down the soil column gradually formed and frost penetration leveled off to a constant value. During this process, there was a marked increase in moisture content across the entire soil. The water mostly gathered in a zone above the cut-fill interface close to the soil surface. At the same time, localized differential settlements on the soil surface were observed, and the maximum settlement was found to take place at the point where the underlying soil moisture content was highest. The analyses showed that cyclic freeze-thaw might be the main cause of the localized concentration of water, whereas capillary action was probably of secondary importance. Therefore, insulation and drainage measures are suggested to be applied during road construction or maintenance to guarantee a favorable performance of the road.