Evaluating the thermal regime and unfrozen water content of snow accumulated in road ditches: a case study from northern Sweden

Snö i vägren påverkar vägens värmeledning under vintern och måste beräknas korrekt för att bedöma vägkonstruktioners hållfasthet i kaltklimat. Forskare vid Luleå tekniska universitet mätte snöns värmeledningsförmåga och vatteninnehål över 49 dagar i norra Sverige för att utveckla bättre prognosmodeller. Resultaten visar att snöns nedre skikt vid markytan hade lägst densitet men inte lägsta värmeledning. Detta basala lager innehöll cirka 3,5 procent ofryst vatten och hölls isotermt omkring 0 °C. Värmeledningen varierade mellan 0,05–0,20 W m⁻¹ K⁻¹ under fryspunkten och 1,0–1,2 W m⁻¹ K⁻¹ vid eller över 0 °C. Studien föreslår en empirisk modell för att uppskatta vägren-snöns isoleringsegenskaper upp till 75 centimeter höjd. Resultaten möjliggör mer tillförlitliga beräkningar för vägar i kaltklimat och kan förbättra infrastrukturplanering i nordisk klimatzon.

<p>Accumulated snow in road ditches significantly influences the thermal regime of road embankments during the winter season. Understanding the insulating effect of this snow cover is essential to accurately assess the thermal behavior of the road structure. However, snow in road ditches differs from naturally accumulated snow due to the presence of traffic-related contaminants and traction materials introduced during winter road maintenance. A field experiment was conducted in Luleå, northern Sweden, to evaluate the insulating properties of the snow accumulated in a ditch. This study mathematically investigates the thermal conductivity, a key parameter for assessing snow insulation, and the unfrozen water content over a 49-day period, based on in situ temperature and density measurements from the experimental site. The findings reveal that the minimum snow density occurs between the soil–snow interface and approximately 15 cm above it. Although this layer has the lowest density, it did not exhibit the lowest thermal conductivity. This basal layer experienced partial melting, contained an unfrozen water content of about 3.5%, and remained isothermal around 0 °C for most of the observation period. In the upper part of the snowpack, thermal conductivity exhibited greater variability, reflecting the enhanced influence of atmospheric conditions near the snow–air interface. The estimated thermal conductivity ranged from approximately 0.05 to 0.20  W m⁻¹ K⁻¹ when the snow temperature was below the melting point, and from 1 to 1.2  W m⁻¹ K⁻¹when the snow was at or above 0 °C. In addition, this study proposes an empirical formulation for estimating the thermal conductivity of ditch snow from the soil–snow interface up to approximately 75 cm above it. The formulation provides reliable results under climatic conditions similar to those of the study site and can support evaluations of snow insulation in cold-region road ditches. However, formulating an empirical relation for the unfrozen water content was challenging, as the snow experiences altering metamorphic states at different depths, resulting in varying behavior. These findings contribute to the understanding of road structure design in cold regions by incorporating the thermal behavior of snow and guiding snow management strategies to improve embankment durability.</p>