The springtime damage to gravel roads and railways is known as frost heave or frost damage.  

The ground frost status is monitored to ensure the constant safety of the railway network. For sites affected by ground frost, the speed limit restriction is set at 50 - 80 kilometres per hour. The current ground frost status on the railway network is updated on the map below.

The maintenance manager of each railway section actively monitors the frost situation. 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 embankments.

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. The ground ice starts to thaw when the frost ceases to increase. Thawing generally starts from the top layer of the frost. The unthawed ice layer prevents the thaw water from flowing downwards.

The softening soil layer is usually of a 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 conduced through the sleepers to the layer cannot be released through the frost layer, the oversaturated soil layer is disturbed and becomes fluid. 

Frost heaving on the roads

Frost heaving is a recurring problem on gravel roads in spring and, to a lesser extent, in autumn.

Weight restrictions

Weight restrictions have to be imposed on part of the road network affected by frost heaving. This avoids excessive damage to the roads due to heavy traffic and ensures viability for necessary transport.

The 12-ton weight restriction is the most common, but, in exceptional cases, the 4-ton restriction may also be applied. The weight restrictions are not applicable to transport that is considered vital.

A forecast of potential weight restrictions is issued around year end. The forecast will be specified in detail at the beginning of March when the prognosis on the severity of frost heaving is completed. Spring weather conditions are monitored actively, and information on the development of the frost heaving situation and any requirement for the imposition of weight restrictions will be disseminated regularly.

Exceptional permits 

In single, unforeseeable cases, the Centres for Economic Development, Transport and the Environment (ELY Centres) may, for a charge, grant a temporary transport permit for a weight-restricted road. The handling permit considers the necessity of the freight and its gross volume. The permit is granted by the region's ELY Centre. The handling process takes a few working days. The charge for the permit is EUR 89.

Example list of transport requiring an exceptional permit:

-Timber
–Soil
– Fuel (except where warehousing spaces do not allow expected potential freight)
-Industrial fertilisers
-Construction supplies
- Forestry and construction machines
-Special freight

Weight restrictions due to frost heaving

Be prepared for potential weight restrictions due to frost heaving. Purchase all required supplies before the frost-breaking period. For example, construction supplies should be purchased in winter. Otherwise, deliveries may be delayed until late springtime.
Road damage through frost heaving can include frost boils, potholes, ruts, or hollows. New frost damage may arise daily, so all travel requires caution.