Maintenance of gravel roads
When seasonal and weather conditions vary, gravel roads require a variety of measures to remain in suitable condition for traffic use. A gravel road changes in shape and evenness throughout the year, and driving conditions can change rapidly. The loose surface structure moulds itself in a different way than a paved road. Global warming has led to a change in the focus of gravel road winter maintenance in southern and south-western parts of the country from snow ploughing to the prevention of road surface frost heaving.
In the spring, as the ground frost melts within the gravel road network, the damage caused by frost heaving is prevented by imposing weight restrictions and by adding crushed stone to the softest parts of the road. (More information on frost heaving). Springtime roadworks involved reshaping the surface of the row for the summer season so that it is even and has the right gradient. The summer problem of dust generation is prevented by adding salt – a dust binding agent – during the reshaping work. In the spring, crushed rock (gravel) can also be added to the wearing course.
The summer maintenance work varies depending on the weather. During dry periods, it may be necessary to repeat dust binding measures if dust is clearly spreading into the areas around the road. Heavy rain can create large numbers of holes in the gravel road, which might make it necessary to level the road surface. However, low levels of unevenness are permitted and do not require any action to be taken.
Even with dry road conditions, unevenness may occur on gravel roads. However, heavy levelling work is not carried out during dry periods, as this normally results in a road that is more uneven than before. The levelling work must wait for moist conditions – only large holes can be filled during dry periods.
In the summer, work is also carried out along the sides of gravel roads, where grass is mown, scrub is cleared, ditches are dug and culverts are repaired and replaced (links to all?). Gravel roads can also be narrowed if they have spread over the years to a size that makes maintenance work difficult.
In the autumn, preparations are made for the start of winter. The road surface is levelled so that it has the right gradient. Crushed rock (gravel) can be added to the wearing course if needed. Climate change has increased the level of surface frost heaving in the autumn (more information on frost heaving à link to frost heaving page). The sun dries the road in the spring, but in the autumn the water does not evaporate from the road surface. At the latest, frost hardens the frost-damaged road surface, so it is important to level the surface just before subzero temperatures arrive.
In winter, it is time for carrying out snow ploughing and also antiskid treatment, which involves either gritting or roughening the surface. Gravel roads are usually within winter maintenance category II or III. (More about winter maintenance categories). In south-western and southern parts of the country, the gravel roads can remain unfrozen throughout the winter, which means that surface frost heaving is a major problem for both the road user and the road maintainer. (More information on frost heaving). In order to ease the frost heaving problems in the spring, the snow banks are cleared from the sides of the road in late winter so that the surface of the road can drain better. Frozen culverts and clogged culvert heads are also opened to ensure that the melting water can drain away.