Aspects of compaction and drying–wetting curves of a subgrade clayey soil

In earthworks, the effect of environmental conditions on compacted soil behaviour is usually complex. One of the major difficulties comes from the coupling of hydraulic and mechanical loadings. This technical note presents some experimental results on compaction and drying–wetting curves in four diagrams: (w, e), (s, e), (w, S_r), (s, S_r), providing a global representation and better understanding of the behaviour of clayey soil under these conditions. The note also presents a comparison of hydraulic and mechanical loadings. In terms of water transfer, hydraulic loading enhances water exchange with the environment, whereas mechanical loading compresses the volume of voids under nearly constant water content conditions. Concerning the fabric, mechanical loading alters both the diameter and the volume of inter-aggregate pores, whereas hydraulic loading affects only the volume. Finally, the comparison highlights how hydraulic and mechanical loadings enhance the saturation of soil in opposite ways in the degree of saturation against suction or compaction effort plane.