Soil rut depth prediction based on soil strength measurements on typical Estonian soils

Deep ruts in soil hinder the movement of off-road vehicles and harm drastically the soil environment. The aim of this study was to determine the most suitable cone and remoulding index based methods for rut depth estimation for single and repeated military vehicle passage in typical Estonian soils. Cone index based sinkage models - US Army ERDC, Maclaurin (1990) and Willoughby and Turnage sinkage models applicable for military vehicles were tested, using different critical layers (0-15 cm, 7.5-23 cm or 15-30 cm). The test vehicles were a 7 Mg truck and a 23 Mg armoured personnel carrier. At eight experimental sites covering mechanically very variable soil conditions (from peat to clay soil), rut depth was measured after one and ten vehicle passes, cone penetration tests were conducted in situ, and samples were collected for determination of bulk density, organic carbon content, texture, gravimetric water content, plastic and liquid limits of the topsoil and subsoil. According to average RMSD values for military truck the Willoughby and Turnage model was the most accurate prediction method. For one pass and 10 passes the rating cone index values from the 7.5-23 cm and 15-30 cm soil layer, respectively, produced the lowest RMSD values.