Frost heave and water uptake rates in silty soil subject to variable water table height during freezing

Given a frost-susceptible soil and a sufficiently cold environment, the availability of water is the most influential factor controlling frost heave in pavement structures. In particular, the depth of the water table below the freezing front determines to a large degree the availability of new water that can be imbibed by freezing pavement layers. This research investigated the effect of water table height on the laboratory frost heave behavior of an undisturbed silty soil typical of frost-susceptible pavement subgrades within the jurisdiction of the Swedish National Road Administration. The tested specimen was 590 mm in height, and the water table was varied between 150 and 300 mm above the bottom of the specimen. A test was also conducted in the absence of a water table. The frost penetration rate was maintained at 1.1 mm/hr throughout the testing to facilitate a similar rate of heat extraction for each frost heave test, and the same depth section of the specimen was analyzed for each test. The test results show consistent and measurable reductions in frost heave and water uptake rates with decreasing water table height. However, the frost heave rate declined more slowly than the water uptake rate, leading to increasing ratios of volumetric frost heave to volumetric water uptake. This observation is explained by the intrusion of increasing amounts of air into the frozen zone during tests utilizing lower water tables.