Frost Heave and Thaw Settlement Estimation of a Frozen Ground

This paper presents various methods employed to estimate the frost heave and thaw settlement of the frozen ground beneath an ice rink facility in Myllypuro, eastern Helsinki, Finland. The ground below the ice rink had been frozen for many years since it was opened in 1976. The subsoil reached freezing conditions due to a malfunction in the heating system and the freezing front continued to penetrate into the ground. Over the years, significant frost heave caused deformations to the facility and in 2012, it forced an immediate renovation. A new foundation system comprised of a well-insulated concrete floor-slab and a group of 240 steel thermal piles was adopted in the renovation. Formation of a tight contact between the pile and the frozen soil could create excessive negative skin friction and therefore, such situation should be avoided. This was achieved by thawing the frozen soil adjacent to individual piles. A warm liquid was circulated through U-type plastic tubes embedded inside the piles down to the measured frost depth of around 5 m to 6 m. Upon the completion of the renovation, several undisturbed soil samples were taken and characterized for frost susceptibility. Laboratory frost cell tests were carried out to estimate the possible future frost heave and thaw settlements. Frost heave and thaw settlement were also calculated from various empirical formulations and compared with the estimations based on the laboratory test results. The thaw settlement estimations from the empirical formulations resulted in a maximum thaw settlement of around 1.8 m within 6.6 m frost depth (~27 % of the total frost depth). On the other hand, the maximum thaw settlement estimations based on the frost cell test results was around 1.84 m (~28 % of the total frost depth). The calculated frost depth and frost heave at the end of 30 years was around 6.39 m and 622 mm, respectively. This was in good agreement with the in-situ measuments taken immediately before the renovation, after about 30 years of continuous operation.