A concept of compaction

Bulk density data of about 150 soil profiles from America, Europe and Asia were used to obtain the regression curve of void ratio ? as a function of vertical stress σ_z. For virgin soils straight lines were obtained if a linear scale was used for ? and a logarithmic scale for σ_z. The slope of these lines was steepest for forest zone soils, less steep in soils of high-grass zones and flattest in short-grass soils. This difference is attributed to varying amounts of loosening by bio- and cryoturbation. Thus the compaction state of virgin soils is that of normal compaction caused by pedogenic processes which are superimposed on previous strong overconsolidation due to desiccation. Against this background agricultural land use creates overconsolidation in the upper soil layers, which is particularly pronounced when the previous bioturbate action has been strong. Young soil deposits cannot develop normal compaction, because of the lack of previous drying of the whole profile.