Determining Minimum Radius Length of Circle Horizontal Curves According to Pavement Damages

Finding a minimum allowable radius length of a circle horizontal curve is essential to reduce earthwork cost or damage to the forest ecosystem, as well as make driving more comfortable. The present study is conducted i) to analyze different radius lengths of circle horizontal curves using an integrated approach consists of a Civil3D in concert with the field surveys, and ii) to propose a set of geometric design criteria which are more consistent with the existing condition of forest road network in Hyrcanian forest, north of Iran. Depth of the rutting (i.e., machine footprint) and soil mechanical properties are examined for a total of 36 existing horizontal curves with different radius lengths. Further, technical characteristics (i.e., stopping sight distance, horizontal sight line offset and turning speed) and a few parameters on pavement damage are included and incorporated into the research objective. No-statistical differences between radius lengths of the horizontal curve for classes of 10-15 and 16-20 m may associate with dissimilarity in the soil mechanical properties and in the dimension of the rut depth. These findings confirmed that it is therefore possible to shorten allowable radius length of a circle horizontal curve to at least 12 m under a longitudinal slope of 5% for forest road network in the north of Iran.