Soil water retention curves representing two tropical clay soils from Sudan

Soil water retention curves (SWRCs) form an essential component of frameworks coupling the hydromechanical behaviour of unsaturated soils. The curves describe how suction changes with variables such as degree of saturation. SWRCs can be determined from incrementally drying initially saturated reconstituted samples to a final residual state, thus developing the primary drying curve (PDC). The primary wetting curve (PWC) is established from subsequent incremental wetting and is hysteretic compared with the PDC. SWRCs for two reconstituted, high-plasticity, tropical clays from Sudan have been determined using the filter paper technique, for which the maximum measurable suction is 30 MPa. At this suction the degree of saturation for both soils was greater than 40% and did not reduce much further on full drying under ambient laboratory conditions. Thus the primary SWRCs did not develop into the usual sigmoidal shape expected. The development of SWRCs under various subsequent cycles of wetting and drying are presented and discussed along with details concerning volumetric changes and cracking during drying. In order to investigate the uniqueness of the PDC and PWC and the effect of initial void ratio, SWRCs were determined for samples formed by dynamic and static compaction under different applied energy levels and also for intact samples. These were found to be located to the left of the PDC and often the PWC too.