Assessment of Unpaved Forest Road Surface Condition based on Slope Steepness and Bearing Capacity

Aims: The technical health of forest road surfaces has an important role in the continuation of access to the forest and the safety of vehicle traffic. The objective of this research was to investigate the effect of longitudinal slope of forest roads and climate conditions on the unpaved road surface condition. Material & Methods: ۵۰۰-meter road segments were randomly determined in Mediterranean, sub-humid and semi-arid climates. In Each climate, sample units on roads were divided into slope classes of <۵% and >۵% and the UPCI values were calculated in field survey. In each of road segments three soil samples were collected for California bearing ratio (CBR) analysis. Proctor and CBR tests were conducted according to ASTM standards for each slope classes. Findings: Results indicated that in slope class<۵%, UPCI value in sub-humid region was significantly lower than other climates (P<۰.۰۵). Maximum UPCI was observed for roads located in semi arid climate. In addition, an increase in slope classes from <۵% to >۵% can decrease UPCI by about ۶.۶%, ۱۱.۸% and ۱۱.۱% in Mediterranean, semi arid and sub-humid climates, respectively. There was a positive and significant correlation between soil CBR and UPCI variables in all climates. Indeed, for roads with high bearing capacity, the condition of the top layer was more suitable. Conclusion: More knowledge about the effects of slope gradient and climate on road surface quality is necessary to decrease the negative effects of traffic on steep slopes in the mountainous forests.

کلیدواژه ها:

Slope gradient ، Unpaved Road Condition Index ، Field survey.