Influence of logging traffic on physical and mechanical properties of a loamy leached soil in the Soignes Forest [Brussel, Belgium]. In a even-aged high forest of beech in the Soignes Forest (near Brussels, Belgium), both intact and remoulded soil samples were taken in reference and adjacent wheel-rutted areas. Simultaneously, in the same areas, penetration tests were performed on the field. Local soils are argillic brown earths. The soil of the study, with an eluvial E horizon associated with an illuvial Bt horizon (clay accumulation), is a leached brown soil developed on loessic parent materials. In this forest site, soil compaction results from timber harvesting using a Timberjack engine (9.6 tons, 130 HP). Our determinations show clear perturbations in the Eg and Btg horizons of the wheel-rutted soil, where qc is greater than in the reference soil (E and Bt horizons). These observations bear out previous results which showed that in the wheel-rutted areas soil macroporosity decreases to less than 10/ of the total soil volume. Mechanical laboratory tests show the following trends: - The wheel-rutted profile effective cohesion (c') and compressive strength (sigma c) are greater than those on the reference area. - The dry unit weight is higher in the wheel-rutted area than in the reference soil; consequently, void ratio (e) and porosity (n) are lower in the disturbed area. - The optimum Proctor's evolution with the compaction energy is reversed for the eluvial and the illuvial horizons. All these results provide evidence that in the studied soils logging traffic leads to the degradation of both physical and mechanical soil properties.