The effect of gravel cover characteristics on dust control of Arab-Dagh forest roads in Golestan province

The forest road network in Golestan province is often gravel or dirt. The main problem of dirt roads, especially in the summer season, is the generation of dust due to vehicle traffic, which causes discomfort and annoyance to tourists, reduces the visibility of vehicles behind, and consequently reduces traffic safety. The aim of the present study is to investigate the effect of gravel cover characteristics on dust control of Arab-Dagh forest roads in Golestan province. For this purpose, a portable wind tunnel device with a contact surface measuring 60 × 38 cm was used. The device was transported to the desired area by passenger car and started up with the help of a mobile electric motor. Parts of the road that were uniform in terms of longitudinal slope, curvature, width of passage and other technical aspects were randomly selected and then gravel covering in the dimensions of small rubble (larger than 3 cm), almonds (1.5-3 cm) and gravel (smaller than 1.5 cm) with a surface coverage of 0 or control, 25, 50 and 75 percent of the thickness of the gravel was sprayed separately to the size of the contact surface of the wind tunnel. In the next stage, the compaction operation was carried out using a non-mechanized (manual) smooth cylindrical roller. In the next stage, by deploying and operating the device on the sample parts, the road surface was exposed to winds with speeds of 2 and 4 meters per second. These speeds were derived from the wind speed created by the fast traffic of cars on the road. The duration of the wind effect on all parts was considered the same and equal to 2 minutes. Then, the collected dust was weighed inside the plastic silicones with an accuracy of 0.1 mm. The experiments were carried out as a factorial in a randomized complete block design. The results showed that the highest amount of dust reduction was achieved in the small gravel treatment with 75% coverage. In this treatment, 81 and 71% reduction in the amount of dust from the plots located in the wind tunnel was reported at wind speeds of 2 and 4 m/s, respectively. In the almond gravel treatment with 75% coverage and at wind speeds of 2 and 4 m/s, the amount of dust was reduced by 44% and 50%, respectively. In the case of the gravel treatment with 75% coverage, the amount of dust reduction was 44% at both wind speeds. In all gravel treatments, the highest amount of dust from the plots located in the wind tunnel was recorded at 25% coverage. Also, with increasing percentage of coverage of the gravel treatments, the amount of dust decreased. All three gravel treatments were able to significantly reduce the amount of dust generated by the wind tunnel plots compared to the control treatment. However, the most effective treatment was the small gravel treatment. Thus, the use of small gravel with coverage of 75% can be suggested as the most suitable type of gravel cover for the protection of forest roads in the Arab-Dagh region.