Estimation of the Risk of Rutting on Forest Roads during the Spring Thaw

The purpose of this study was to determine whether portable devices for measuring the bearing capacity of an unpaved road can be used to evaluate the extent of damage caused by heavy vehicles during the spring thaw. A portable bearing capacity measurement device is easily transported—for example, in a forester's car—where it is available for quick use. In the spring of 2012 and 2013, E moduli were measured by dynamic cone penetration, light falling weight deflectometer, and falling weight deflectometer devices a few days before loading runs were performed on forest roads. The measurements were made at 10 test sites, half of which were located on mineral soil and half on peat. The profiles of the road surfaces at the test sites were determined by mobile laser scanning before and after the loading runs to indicate rutting at the measurement points. Rutting was converted into rut depth increase per pass of the truck used. A comparison of the E moduli determined with the different measurement devices in relation to the rutting revealed that each device had a threshold value below which the tendency and depth of rutting increased. These threshold values will help in evaluating whether timber loads can be transported via the forest road during frost thawing. The applicability of the results must still be verified in actual operating conditions.