Prediction of Frost Depth Penetration and Frost Heave in Frost Susceptible Soils

摘要

The natural freezing and thawing of soils can dramatically affect their thermal and mechanical properties, which can have destructive effects on structures built upon those soils. Previous testing in this field has attempted to predict the frost penetration depth, based on the soil, thermal, and hydrodynamic properties. A thermodynamic finite element model was developed using multiple frost-susceptible soil types tested with a variety of moisture conditions. Thermal conductivity and temperature were measured throughout several multi-day freeze-thaw cycles. It was identified that moisture migration was likely the most significant factor in frost heave and frost penetration, as free water sources in porous soils produced the largest deformations, while there was minimal heave in other frost susceptible materials. The thermal conductivity was found to increase near the freezing front across all samples, such as for low-plasticity silt soils where the thermal conductivity rose from 301 to 357 milliBTU/(hr*ft*℉), which was theorized to correspond to where the moisture was concentrated, and ice formation was highest. This guided the finite element model development by incorporating moisture flow and porosity, along with other parameters with respect to time, temperature, and ice and moisture production during freeze-thaw cycles. This was found to improve frost depth prediction compared to the standard modified Berggren equation, where for our tested conditions the equation had an error of 2.2 inches for a frost depth of 8 inches, while our model had an error of 1.4 inches for the same depth. These developments will be of great importance to airfield runway and general pavements design and maintenance in frost-affected regions, allowing for a more accurate prediction of frost depth and deflection during freezing and thawing periods, and expected frost heave damage across multiple seasons.