Equilibrium moisture profiles in consolidating, sulfidic, coastal clay soils

Large areas of soft sulfidic coastal clay soils are being developed around the world. These soils can be up to 40m deep, have shallow watertables and volumetric water contents approaching 80%. They pose significant problems and frequently require costly consolidation. Swelling soil theory, developed for industrial slurries is directly applicable to these soils. Here, simple analytic expressions for equilibrium moisture contents in consolidating soils are derived using an analytic moisture characteristic that is consistent with both diffuse double layer theory and measurements on coastal clay soils. Consolidation from applied surface loads, falling watertables and increases in the soil solution electrolyte concentration are considered. The total buoyant specific solid volume per unit surface area is identified as an important scaling parameter. Effective consolidation requires that applied surface loads exceed this parameter. Predictions of chemical consolidation are based on the untested assumption that relative results for clay slurries are directly applicable to these soils. The predictions show that modest increases in electrolyte concentrations can produce significant consolidation, in some cases comparable with that produced by an applied surface load of 40 tonnes/m². Increasing the charge of the electrolytes has a dramatic impact on consolidation. These predictions remain to be tested.