Frost damage to railway tracks
The ground frost status is monitored to ensure the safety of the railway network. The maintenance manager of each track section monitors the frost situation actively. For sites affected by ground frost, the speed limit restriction is set at 50 - 80 kilometres per hour.
Ground frost damages are prevented by proactively opening and clearing drainage culverts and ditches to allow the free flow of water and the drying of the trackbed.
How does ground frost affect the railway network?
The ground frost manifestations significant to track structures are massive ground ice and layered ground ice. Massive ground ice refers to an ice layer formation during wintertime, the total volume of which remains unchanged. Soil types which allow the formation of massive ice are called non-heaving soil types.
The causative factor of ground frost problems is layered ground ice. Layered ground ice is an ice formation where mainly horizontal ice layers of varying thickness and ice lenses alternate with partially non-frozen layers and massive ice layers. In the formation of layered ground ice, the soil layers expand, causing uneven ground frost heaving. Soil types which allow the formation of layered ground ice are called heaving soil types.
A phenomenon called soil freeze-thaw is closely associated with ground frost. The phenomenon relates to the thawing of ground ice. Thawing generally starts from the top layer of the frost. The unthawed ice layer prevents the thaw water from flowing downwards. The unfrozen soil layer is saturated with water and becomes soft.
The softening soil layer is usually of fine grained soil type. Rain and thaw waters import fine-grained soil from the uppermost gravel layer to the unfrozen layer. When the pressure generated by a train conducted through the sleepers to the layer cannot be released through the frost layer, the oversaturated soil layer is disturbed and becomes fluid.