Bearing Capacity of Forest Roads On Poor-Bearing Road Subgrades Reinforced With Timber Rollers and Willow Brushwood Mats

Clay and silt loam soils are weak road surfaces that require reinforcement, in order to obtain the load-bearing parameters of the entire road structure to allow transport related to forest management. It concerns especially the transport of round wood by heavy-duty vehicles, regardless of weather conditions. The research was carried out on a forest road on the territory of the State Forests in Poland, in the Brzeziny Forest District, where eight test sections with a total length of 422 m were made with different pavement structures on a weak-bearing soil substrate (clay, silt loam). The pavement structure was designed using crushed aggregates 0/31.5 mm and sand-gravel mix, sand-gravel mix 0/63 mm, 400 g·m-2 geotextile, on a sub-base reinforced with wood rollers (pine or oak) and willow mats. A reference road section without road base reinforcement was carried out only with the profiling of the existing pavement and a new layer of aggregate. The bearing capacity of the pavement was determined based on the static strain modulus ME determined by measuring with a VSS MN·m-2 plate, the dynamic deformation modulus Evd MN·m-2 obtained from lightweight deflectometer measurements. The compacted state of the pavement was determined by the strain index I0. It has been shown that pavements made of crushed aggregate and common gravel on timber roller substructure are characterized by good bearing capacity parameters, where the average values of secondary modulus of strain are above 130 MN·m-2. Pavements on weak-bearing soils reinforced with willow brushwood mats have low bearing capacity parameters, with averages of 26.09 ≤ MEII ≤ 53.93 and 22.1 ≤ Evd ≤ 39.1 MN·m-2.